Android

Read more about the article Making App Name Configurable for Open Event Organizer App

Making App Name Configurable for Open Event Organizer App

Open Event Organizer is a client side android application of Open Event API server created for event organizers and entry managers. The application provides a way to configure the app name via environment variable app_name. This allows the user to change the app name just by setting the environment variable app_name to the new name. I will be talking about its implementation in the application in this blog.

Generally, in an android application, the app name is stored as a static string resource and set in the manifest file by referencing to it. In the Organizer application, the app name variable is defined in the app’s gradle file. It is assigned to the value of environment variable app_name and the default value is assigned if the variable is null. The relevant code in the manifest file is:

def app_name = System.getenv('app_name') ?: "eventyay organizer"

app/build.gradle

The default value of app_name is kept, eventyay organizer. This is the app name when the user doesn’t set environment variable app_name. To reference the variable from the gradle file into the manifest, manifestPlaceholders are defined in the gradle’s defaultConfig. It is a map of key value pairs. The relevant code is:

defaultConfig {
   ...
   ...
   manifestPlaceholders = [appName: app_name]
}

app/build.gradle

This makes appName available for use in the app manifest. In the manifest file, app name is assigned to the appName set in the gradle.

<application
   ...
   ...
   android:label="${appName}"

app/src/main/AndroidManifest.xml

By this, the application name is made configurable from the environment variable.

Links:
1. ManifestPlaceholders documentation
2. Stackoverflow answer about getting environment variable in gradle

Continue ReadingMaking App Name Configurable for Open Event Organizer App
Read more about the article Adding Number of Sessions Label in Open Event Android App

Adding Number of Sessions Label in Open Event Android App

The Open Event Android project has a fragment for showing tracks of the event. The Tracks Fragment shows the list of all the Tracks with title and TextDrawable. But currently it is not showing how many sessions particular track has. Adding TextView with rounded corner and colored background showing number of sessions for track gives great UI. In this post I explain how to add TextView with rounded corner and how to use Plurals in Android.

1. Create Drawable for background

Firstly create track_rounded_corner.xml Shape Drawable which will be used as a background of the TextView. The <shape> element must be the root element of Shape drawable. The android:shape attribute defines the type of the shape. It can be rectangle, ring, oval, line. In our case we will use rectangle.

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <corners android:radius="360dp" />

    <padding
        android:bottom="2dp"
        android:left="8dp"
        android:right="8dp"
        android:top="2dp" />
</shape>

 

Here the <corners> element creates rounded corners for the shape with the specified value of radius attribute. This tag is only applied when the shape is a rectangle. The <padding> element adds padding to the containing view. You can modify the value of the padding as per your need. You can feel shape with appropriate color using <solid> as we are setting color dynamically we will not set color here.

2. Add TextView and set Drawable

Now add TextView in the track list item which will contain number of sessions text. Set  track_rounded_corner.xml drawable we created before as background of this TextView using background attribute.

<TextView
        android:id="@+id/no_of_sessions"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/track_rounded_corner"
        android:textColor="@color/white"
        android:textSize="@dimen/text_size_small"/>

 

Set color and text size according to your need. Here don’t add padding in the TextView because we have already added padding in the Drawable. Adding padding in the TextView will override the value specified in the drawable.

3.  Create TextView object in ViewHolder

Now create TextView object noOfSessions and bind it with R.id.no_of_sessions using ButterKnife.bind() method.

public class TrackViewHolder extends RecyclerView.ViewHolder {
    ...

    @BindView(R.id.no_of_sessions)
    TextView noOfSessions;

    private Track track;

    public TrackViewHolder(View itemView, Context context) {
        super(itemView);
        ButterKnife.bind(this, itemView);

    public void bindTrack(Track track) {
        this.track = track;
        ...
    }   
}

 

Here TrackViewHolder is a RecycleriewHolder for the TracksListAdapter. The bindTrack() method of this view holder is used to bind Track with ViewHolder.

4.  Add Quantity Strings (Plurals) for Sessions

Now we want to set the value of TextView. Here if the number of sessions of the track is zero or more than one then we need to set text  “0 sessions” or “2 sessions”. If the track has only one session than we need to set text “1 session” to make text meaningful. In android we have Quantity Strings which can be used to make this task easy.

<resources>
    <!--Quantity Strings(Plurals) for sessions-->
    <plurals name="sessions">
        <item quantity="zero">No sessions</item>
        <item quantity="one">1 session</item>
        <item quantity="other">%d sessions</item>
    </plurals>
</resources>

 

Using this plurals resource we can get appropriate string for specified quantity like “zero”, “one” and  “other” will return “No sessions”, “1 session”, and “2 sessions”. accordingly. 2 can be any value other than 0 and 1.

Now let’s set background color and test for the text view.

int trackColor = Color.parseColor(track.getColor());
int sessions = track.getSessions().size();

noOfSessions.getBackground().setColorFilter(trackColor, PorterDuff.Mode.SRC_ATOP);
noOfSessions.setText(context.getResources().getQuantityString(R.plurals.sessions,
                sessions, sessions));

 

Here we are setting background color of textview using getbackground().setColorFilter() method. To set appropriate text we are using getQuantityString() method which takes plural resource and quantity(in our case no of sessions) as parameters.

Now we are all set. Run the app it will look like this.

Conclusion

Adding TextView with rounded corner and colored background in the App gives great UI and UX. To know more about Rounded corner TextView and Quantity Strings follow the links given below.

Continue ReadingAdding Number of Sessions Label in Open Event Android App
Read more about the article Using ThreeTenABP for Time Zone Handling in Open Event Android

Using ThreeTenABP for Time Zone Handling in Open Event Android

The Open Event Android project helps event organizers to organize the event and generate Apps (apk format) for their events/conferences by providing API endpoint or zip generated using Open Event server. For any Event App it is very important that it handles time zone properly. In Open Event Android App there is an option to change time zone setting. The user can view date and time of the event and sessions in Event Timezone and Local time zone in the App. ThreeTenABP provides a backport of the Java SE 8 date-time classes to Java SE 6 and 7. In this blog post I explain how to use ThreeTenABP for time zone handling in Android.

Add dependency

To use ThreeTenABP in your application you have to add the dependency in your app module’s build.gradle file.

dependencies {
      compile    'com.jakewharton.threetenabp:threetenabp:1.0.5'
      testCompile   'org.threeten:threetenbp:1.3.6'
}

Initialize ThreeTenABP

Now in the onCreate() method of the Application class initialize ThreeTenABP.

AndroidThreeTen.init(this);

Create getZoneId() method

Firstly create getZoneId() method which will return ZoneId according to user preference. This method will be used for formatting and parsing dates Here showLocal is user preference. If showLocal is true then this function will return Default local ZoneId otherwise ZoneId of the Event.

private static ZoneId geZoneId() {
        if (showLocal || Utils.isEmpty(getEventTimeZone()))
            return ZoneId.systemDefault();
        else
            return ZoneId.of(getEventTimeZone());
}

Here  getEventTimeZone() method returns time zone string of the Event.

ThreeTenABP has mainly two classes representing date and time both.

  • ZonedDateTime : ‘2011-12-03T10:15:30+01:00[Europe/Paris]’
  • LocalDateTime : ‘2011-12-03T10:15:30’

ZonedDateTime contains timezone information at the end. LocalDateTime doesn’t contain timezone.

Create method for parsing and formating

Now create getDate() method which will take isoDateString and will return ZonedDateTime object.

public static ZonedDateTime getDate(@NonNull String isoDateString) {
        return ZonedDateTime.parse(isoDateString).withZoneSameInstant(getZoneId());;
}

 

Create formatDate() method which takes two arguments first is format string and second is isoDateString. This method will return a formatted string.

public static String formatDate(@NonNull String format, @NonNull String isoDateString) {
        return DateTimeFormatter.ofPattern(format).format(getDate(isoDateString));
}

Use methods

Now we are ready to format and parse isoDateString. Let’s take an example. Let “2017-11-09T23:08:56+08:00” is isoDateString. We can parse this isoDateString using getDate() method which will return ZonedDateTime object.

Parsing:

String isoDateString = "2017-11-09T23:08:56+08:00";

DateConverter.setEventTimeZone("Asia/Singapore");
DateConverter.setShowLocalTime(false);
ZonedDateTime dateInEventTimeZone = DateConverter.getDate(isoDateString);

dateInEventTimeZone.toString();  //2017-11-09T23:08:56+08:00[Asia/Singapore]


TimeZone.setDefault(TimeZone.getDefault());
DateConverter.setShowLocalTime(true);
ZonedDateTime dateInLocalTimeZone = DateConverter.getDate(dateInLocalTimeZone);

dateInLocalTimeZone.toString();  //2017-11-09T20:38:56+05:30[Asia/Kolkata]

 

Formatting:

String date = "2017-03-17T14:00:00+08:00";
String formattedString = formatDate("dd MM YYYY hh:mm:ss a", date));

formattedString // "17 03 2017 02:00:00 PM"

Conclusion

As you can see, ThreeTenABP makes Time Zone handling so easy. It has also support for default formatters and methods. To learn more about ThreeTenABP follow the links given below.

Continue ReadingUsing ThreeTenABP for Time Zone Handling in Open Event Android
Read more about the article Burst Camera Mode in Phimpme Android

Burst Camera Mode in Phimpme Android

Camera is an integral part of core feature in Phimpme Android. Various features were added in the camera part such as resolution, timer, shutter sound, white balance etc. Click burst shot from camera is also an important feature to be added. Burst shot is clicking multiple pictures in one go.

Adding a Burst mode in Phimpme Camera

  • Adding burst mode enable entry in options

The popup view in Camera is added programmatically in app. Setting up the values from sharedpreferences. It takes the value and set burst mode off, 1x, 2x etc. according to value.

final String[] burst_mode_values = getResources().getStringArray(R.array.preference_burst_mode_values);
  String[] burst_mode_entries = getResources().getStringArray(R.array.preference_burst_mode_entries);
String burst_mode_value = sharedPreferences.getString(PreferenceKeys.getBurstModePreferenceKey(), "1");

Two methods created for setting up the previous and next values. To set up the previous value we need to check the current value to be not equal to -1 and greater that zero. Upgrade or downgrade the value of burst mode, according to the click.

public int onClickPrev() {
         if( burst_mode_index != -1 && burst_mode_index > 0 ) {
            burst_mode_index--;
            update(); ...
}

public int onClickNext() {
            if( burst_mode_index != -1 && burst_mode_index < burst_mode_values.length-1 ) {
              burst_mode_index++;
            update();...
}

  • Saving the value in sharedpreferences

So on clicking the previous and next, the value of burst mode value will be updated. As shown in the above code snippet, after every increment and decrement the values set on view and called update method to update the value in the sharedpreference as shown below.

private void update() {
        String new_burst_mode_value = burst_mode_values[burst_mode_index];
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(main_activity);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(PreferenceKeys.getBurstModePreferenceKey(), new_burst_mode_value);
editor.apply();}

  • Taking multiple Images

Now in the implementation part, we need to continuously click the image according to the burst value set by the user. So to enable this, first check the value not to be negative and should be greater than zero. Whole iteration work on separate variable named remaining burst photos. The value of the variable decrease after every image click i.e. takePhoto method calls.

if( remaining_burst_photos == -1 || remaining_burst_photos > 0 ) {
  if( remaining_burst_photos > 0 )
     remaining_burst_photos--;
  long timer_delay = applicationInterface.getRepeatIntervalPref();
  if( timer_delay == 0 ) {
     phase = PHASE_TAKING_PHOTO;
     takePhoto(true);
  }
  else {
     takePictureOnTimer(timer_delay, true);
  }
}

Resources:

 

Continue ReadingBurst Camera Mode in Phimpme Android
Read more about the article Implementing Change Password Feature in SUSI Android App using Custom Dialogs

Implementing Change Password Feature in SUSI Android App using Custom Dialogs

Recently a new servlet was implemented on the SUSI Server about changing the password of the logged in user. This feature comes in handy to avoid unauthorized usage of the SUSI Account. Almost all the online platforms have this feature to change the password to avoid notorious user to unethical use someone else’s account. In SUSI Android app this new API was used with a nice UI to change the password of the user. The process is very simple and easy to grasp. This blog will try to cover the API information and implementation of the Change Password feature in the android client.

API Information

For changing the password of SUSI Account of the user, we have to call on  /aaa/changepassword.json

We have to provide three parameters along with this api call:

  1. changepassword:  Email of user (type string) using which user is logged in.
  2. password:  Old password (type string with min length of 6) of the user.
  3. newpassword: New password (type string with min length of 6) of the user.
  4. access_token: An encrypted access_token indicating user is logged in.

Sample Response (Success)

{
  "session": {"identity": {
    "type": "email",
    "name": "YOUR_EMAIL_ADDRESS",
    "anonymous": false
  }},
  "accepted": true,
  "message": "Your password has been changed!"
}

Error Response (Failure). This happens when user is not logged in:

HTTP ERROR 401
Problem accessing /aaa/changepassword.json. Reason:
   Base user role not sufficient. Your base user role is 'ANONYMOUS', your user role is 'anonymous'

Implementation in SUSI Android App

The change password option is located in Settings Activity and displayed only when user is logged in. So, if a logged in user wants to change the password of his/her SUSI AI account, he/she can simply go to the Settings and click on the option. Clicking on the options open up a dialog box with 3 input layouts for:

  1. Current Password
  2. New Password
  3. Confirm New Password

So, user can simply add these three inputs and click “Ok”. This will change the password of their account. Let’s see some code explanation.

  1. When user clicks on the “reset password” option from the settings, the showResetPasswordAlert() method is called which displays the dialog. And when user clicks on the “OK” button the resetPassword method() in the presenter is called passing input from the three input layout as parameters.

settingsPresenter.resetPassword(password.editText?.text.toString(), newPassword.editText?.text.toString(), conPassword.editText?.text.toString())

fun showResetPasswordAlert() {
   val builder = AlertDialog.Builder(activity)
   val resetPasswordView = activity.layoutInflater.inflate(R.layout.alert_reset_password, null)
   password = resetPasswordView.findViewById(R.id.password) as TextInputLayout
   newPassword = resetPasswordView.findViewById(R.id.newpassword) as TextInputLayout
   conPassword = resetPasswordView.findViewById(R.id.confirmpassword) as TextInputLayout
   builder.setView(resetPasswordView)
   builder.setTitle(Constant.CHANGE_PASSWORD)
           .setCancelable(false)
           .setNegativeButton(Constant.CANCEL, null)
           .setPositiveButton(getString(R.string.ok), null)
   resetPasswordAlert = builder.create()
   resetPasswordAlert.show()
   setupPasswordWatcher()
   resetPasswordAlert.getButton(AlertDialog.BUTTON_POSITIVE)?.setOnClickListener {
       settingsPresenter.resetPassword(password.editText?.text.toString(), newPassword.editText?.text.toString(), conPassword.editText?.text.toString())
   }
}
  1. In the resetPassword method, all details about the passwords are checked like:
  1. If passwords are not empty.
  2. If passwords’ lengths are greater than 6.
  3. If new password and confirmation new password matches

   

When all the conditions are satisfied and all the inputs are valid, resetPassword() in model is called which makes network call to change password of the user.

settingModel.resetPassword(password,newPassword,this)

override fun resetPassword(password: String, newPassword: String, conPassword: String) {
   if (password.isEmpty()) {
       settingView?.invalidCredentials(true, Constant.PASSWORD)
       return
   }
   if (newPassword.isEmpty()) {
       settingView?.invalidCredentials(true, Constant.NEW_PASSWORD)
       return
   }
   if (conPassword.isEmpty()) {
       settingView?.invalidCredentials(true, Constant.CONFIRM_PASSWORD)
       return
   }

   if (!CredentialHelper.isPasswordValid(newPassword)) {
       settingView?.passwordInvalid(Constant.NEW_PASSWORD)
       return
   }

   if (newPassword != conPassword) {
       settingView?.invalidCredentials(false, Constant.NEW_PASSWORD)
       return
   }
   settingModel.resetPassword(password,newPassword,this)
}

Summary

So, this blog talked about how the Change Password feature is implemented in SUSI Android App. This included how a network call is made, logic for making network, information about API, making dialogs with custom UI, etc. So, If you are looking forward to contribute to SUSI Android App, this can help you a little. But if not so, this may also help you in understanding and how you can implement a dialog box with custom UI.

References

  1. To know about servlets https://en.wikipedia.org/wiki/Java_servlet
  2. To see how to implement one https://www.javatpoint.com/servlet-tutorial
  3. To see how to make network calls in android using Retrofit https://guides.codepath.com/android/Consuming-APIs-with-Retrofit
  4. Official docs for displaying dialog https://developer.android.com/guide/topics/ui/dialogs.html
  5. Implementing dialog boxes with custom UI https://stackoverflow.com/questions/13341560/how-to-create-a-custom-dialog-box-in-android
  6. Pull Request for API reference: https://github.com/fossasia/susi_server/pull/352
Continue ReadingImplementing Change Password Feature in SUSI Android App using Custom Dialogs
Read more about the article Uploaded Images History in Phimpme Android

Uploaded Images History in Phimpme Android

In Phimpme Android one core feature is of sharing images to many different platforms. After sharing we usually wants to look in the our past records, where we uploaded what pictures? Which image we uploaded? What time it was? So I added a feature to view the upload history of images. User can go to the Upload history tab, present in the navigation drawer of the app. From there he can browse the repository.

How I added history feature in Phimpme

  • Store the data when User initiate an upload

To get which data uploading is in progress. I am storing its name, date, time and image path. When user approve to upload image from Sharing Activity.

Created a database model

public class UploadHistoryRealmModel extends RealmObject{

   String name;
   String pathname;
   String datetime;

   public String getName() {
       return name;
   }

   public void setName(String name) {
       this.name = name;
   }

   public String getPathname() {
       return pathname;
   }

   public void setPathname(String pathname) {
       this.pathname = pathname;
   }

   public String getDatetime() {
       return datetime;
   }

   public void setDatetime(String datetime) {
       this.datetime = datetime;
   }
}

This is the realm model for storing the name, date, time and image path.

Saving in database

UploadHistoryRealmModel uploadHistory;
uploadHistory = realm.createObject(UploadHistoryRealmModel.class);
uploadHistory.setName(sharableAccountsList.get(position).toString());
uploadHistory.setPathname(saveFilePath);
uploadHistory.setDatetime(new SimpleDateFormat("dd/MM/yyyy HH:mm:ss").format(new Date()));
realm.commitTransaction();

Creating realm object and setting the details in begin and commit Transaction block

  • Added upload history entry in Navigation Drawer

    <LinearLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/ll_drawer_uploadhistory"
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:background="@drawable/ripple"
   android:clickable="true"
   android:orientation="horizontal">

   <com.mikepenz.iconics.view.IconicsImageView
       android:id="@+id/Drawer_Upload_Icon"
       android:layout_width="@dimen/icon_width_height"
       android:layout_height="@dimen/icon_width_height"
       app:iiv_icon="gmd-file-upload"/>

   <TextView
       android:id="@+id/Drawer_Upload_Item"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="@string/upload_history"
       android:textColor="@color/md_dark_background"
       android:textSize="16sp"/>
</LinearLayout>

It consist of an ImageView and TextView in a horizontal oriented Linear Layout

  • Showing history in Upload History Activity

Added recyclerview in layout.

<android.support.v7.widget.RecyclerView
   android:id="@+id/upload_history_recycler_view"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:layout_below="@id/toolbar">
</android.support.v7.widget.RecyclerView>

Query the database and updated the adapter of Upload History

uploadResults = realm.where(UploadHistoryRealmModel.class);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
uploadHistoryRecyclerView.setLayoutManager(layoutManager);
uploadHistoryRecyclerView.setAdapter(uploadHistoryAdapter);

Added the adapter for recycler view and created an Item using Constraint layout.

Resources

Continue ReadingUploaded Images History in Phimpme Android
Read more about the article Using RecyclerView Instead Of ViewPager For Gallery

Using RecyclerView Instead Of ViewPager For Gallery

Phimpme is an Image app that provide camera, editing ,sharing options and a gallery section. The Gallery section allows us to view large number of images that are locally available in the users device. Generally developers used viewpager to swipe the horizontal images although we are also using viewPager but the problem is it is taking more time to load large size images and that disturb the user smooth experience. After so much research I came to new solution. So in this post, I will be explaining how to use recyclerview to view gallery images instead of viewPager.

Let’s get started

Make sure you have Recyclerview support in your dependencies in build.gradle. As recyclerView required an adapter and viewHolder to set data in recyclerView. So I will be explaining about adapter.

ViewHolder for RecyclerView

public static class ViewHolder extends RecyclerView.ViewHolder {
  ImageView imageView;
  LinearLayout linearLayout;

  public ViewHolder(View itemView) {
      super(itemView);
      imageView = new ImageView(context);
      linearLayout = (LinearLayout) itemView.findViewById(R.id.layout);
      WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
      Display display = wm.getDefaultDisplay();
      Point size = new Point();
      display.getSize(size);
      int width = size.x;
      int height = size.y;
      LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
              width, height);
      imageView.setLayoutParams(params);
      imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
      linearLayout.addView(imageView);
  }
}

Right now the imageView is adjusting according to device screen size so that it will be compatible with all devices.

I am passing the width and height in LayoutParams to parent of imageview i.e in our case linearlayout is parentView.

Adapter for RecyclerView

public ImageAdapter(ArrayList<Media> media) {
  this.media = media;
}

@Override
public ImageAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
  View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.unit_image_pager, null, false);

  return new ViewHolder(view);
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
  Glide.with(getContext())
          .load(media.get(position).getUri())
          .diskCacheStrategy(DiskCacheStrategy.SOURCE)
          .thumbnail(0.5f)
          .into(holder.imageView);
  holder.imageView.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
          basicCallBack.callBack(0,null);
      }
  });
}

MediaList is an arrray of media that contains the list of images with URI that will help to load images. I am using Glide to load images you can use any library to load images. Adapter helps to load data in recyclerView.

Now set viewPager where you require to scroll images horizontally

@Nullable @BindView(R.id.photos_pager)
RecyclerView mRecylerPager;
mRecylerPager.setLayoutManager(linearLayoutManager);
mRecylerPager.setHasFixedSize(true);
mRecylerPager.setLongClickable(true);

Our recycler view is ready now the most important part is to set things onPageChangeListner. For example : In Phimpme we are getting path of current position image to show in image description so to update the value we are writing that codde in onPageChangeListner and to update the toolbar.

mViewPager.setOnPageChangeListener(new PagerRecyclerView.OnPageChangeListener() {
  @Override
  public void onPageChanged(int oldPosition, int position) {
      getAlbum().setCurrentPhotoIndex(position);
      toolbar.setTitle((position + 1) + " " + getString(R.string.of) + " " + size_all);
      invalidateOptionsMenu();
      pathForDescription = getAlbum().getMedia().get(position).getPath();
  }
});

To scroll to the given position we require to set the position to recyclerView and it can be done by the following code

mViewPager.scrollToPosition(getCurrentPsotion());

This is how I implemented the recyclerView instead of ViewPager to load gallery images faster as compare to ViewPager.

RecyclerView in Phimpme to load gallery Images

Resources:     

 

Continue ReadingUsing RecyclerView Instead Of ViewPager For Gallery
Read more about the article Electrical Experiments with PSLab

Electrical Experiments with PSLab

PSLab has the capability to perform a variety of experiments. The PSLab Android App and the PSLab Desktop App have built-in support for over 70 experiments which are commonly performed by students. In addition to that, it can be used in other experiments conveniently. This blog post is in continuation with the previous two posts regarding performing experiments (links in the reference) and this blog deals with another category of experiments that can be performed using PSLab.

The blog lists experiments which mainly involve the basic circuit elements like resistors, capacitors and inductors. These experiments involve the study of R-C, L-R, L-C and L-C-R circuits. These circuits have properties which make them important in real life applications and this blog attempts to give a rough picture of their importance.

Ohm’s Law, Capacitive Reactance and Inductive Reactance

These experiments involve the study of each of the basic circuit element individually. The current and voltage characteristics of each of the elements is studied.

The definitions of the above are:

Ohm’s Law – This is a law familiar to most. It relates the voltage and current of a purely resistive circuit stating that the voltage and current are proportional to each other and their ratio is a constant called the resistance. In this case, the current and voltage are in the same phase.

Capacitive Reactance – Across a capacitor in an AC circuit, the current and voltage are not in the same phase and the current leads the voltage. For a purely capacitive circuit, this difference is 90o.

Inductive Reactance –  Across an inductor in an AC circuit, the current and voltage are not in the same phase and the current lags behind the voltage. For a purely inductive circuit, this difference is 90o.

The reactance is given for capacitor and inductor is given by 1/wC and wL respectively, where C & L are the values of capacitance and inductance respectively and w is the frequency of the AC signal.

The circuit for the setup is shown below. We need to observe the plot of the input waveform and the plot of the voltage across individual elements to observe the phase shift.

  1. Connect CH1 & GND across the input terminals and CH2 & GND across the terminals of any of the elements.
  2. An external signal can be used or can be generated using the PSLab. Use the PSLab to generate a sinusoidal signal of frequency 1000 Hz. by connecting the ends of PV1 in the circuit.
  3. Observe the waveforms. In case of the resistor, there should be no observable phase lag between the two. In case of the capacitor and inductor, there will be an observable phase difference of 90o.
  4. For the capacitive and inductive circuits, just replace the resistor in the above circuit with capacitor/inductor.

RC Circuits

Drawing their names from their respective calculus functions, the integrator produces a voltage output proportional to the product (multiplication) of the input voltage and time; and the differentiator (not to be confused with differential) produces a voltage output proportional to the input voltage’s rate of change.

RC Integrator circuit

For constructing the RC integrator circuit, connect the circuit as shown in the diagram.

  • Construction of the integrator circuit is fairly simple once the differentiator circuit is done.
  • Interchange the positions of the capacitor and resistor in the above circuit and the circuit for the integrator is complete.
  • Observe the output waveform. Plot both the CH1 and CH2 data simultaneously to compare the waveforms.

RC Differentiator circuit

For constructing the RC differentiator circuit, connect the circuit as shown in the diagram.

  • The values of resistance and capacitance used here are 10k ohm and 0.01uF.
  • Connect the CH1 and GND pins of the board with the input side marked as Vi. Ensure that GND is connected to the GND of the circuit.
  • Similarly, connect CH2 and GND with the corresponding ends of the output side marked as Vo.
  • PSLab can also be used for supplying the input to the circuit. Connect the ends of W1 and GND across Vi. W1 can be used to generate a square wave of 10V peak to peak voltage with a frequency of 500 Hz.
  • Observe the output waveform. Plot both the CH1 and CH2 data simultaneously to compare the waveforms.

RL Circuits

RL Integrator Circuit.

For constructing the RL integrator circuit, connect the circuit as shown in the diagram.

  • Construction of the integrator circuit is fairly simple once the differentiator circuit is done.
  • Interchange the positions of the inductor and resistor in the above circuit and the circuit for the integrator is complete.
  • Observe the output waveform. Plot both the CH1 and CH2 data simultaneously to compare the waveforms.

RL Differentiator Circuit

For constructing the RL differentiator circuit, connect the circuit as shown in the diagram.

  • The values of resistance and inductance used here are 470 ohm and 10mH.
  • Connect the CH1 and GND pins of the board with the input side marked as Vi. Ensure that GND is connected to the GND of the circuit.
  • Similarly, connect CH2 and GND with the corresponding ends of the output side marked as Vo.
  • PSLab can also be used for supplying the input to the circuit. Connect the ends of W1 and GND across Vi. W1 can be used to generate a square wave of 2V peak to peak voltage with a frequency of 5000 Hz.
  • Observe the output waveform. Plot both the CH1 and CH2 data simultaneously to compare the waveforms.

Frequency Response

Frequency Response of an electric or electronics circuit allows us to see exactly how the output gain (known as the magnitude response) and the phase (known as the phase response) changes at a particular single frequency, or over a whole range of different frequencies from 0Hz, (d.c.) to many thousands of megahertz, (MHz) depending upon the design characteristics of the circuit.

Frequency response of a circuit can be studied using different tools like Bode plots, phase plots etc. However, this blog would limit to using simple RC and RL circuits as they can be easily visualised using an oscilloscope.

RC Circuits

  • For observing the frequency response of RC circuits, the circuit can be constructed as shown below.
  • The values of resistance and capacitance used here are 10k ohm and 0.01uF.
  • Connect the CH1 and GND pins of the board with the input side marked as Vi. Ensure that GND is connected to the GND of the circuit.
  • Similarly, connect CH2 and GND with the corresponding ends of the output side marked as Vo.
  • PSLab can also be used for supplying the input to the circuit. Connect the ends of W1 and GND across Vi. W1 can be used to generate a square wave of 10V peak to peak voltage with a frequencies ranging from 100 Hz to 5000 Hz.
  • Switch to the X-Y mode of the oscilloscope and observe the waveform formed.

RL Circuits

  • For observing the frequency response of RL circuits, the circuit can be constructed as shown below.
  • The values of resistance and inductance used here are 470 ohm and 10mH.
  • Connect the CH1 and GND pins of the board with the input side marked as Vi. Ensure that GND is connected to the GND of the circuit.
  • Similarly, connect CH2 and GND with the corresponding ends of the output side marked as Vo.
  • Note: PSLab in this case cannot be used as an AC source as the maximum frequency of waveforms produced by PSLab is limited to 5kHz. However, this experiment would also need frequencies much higher than 5 Hz i.e upto 50 kHz. So, a dedicated function generator is needed. However, the oscilloscope would work just fine.
  • Switch to the X-Y mode of the oscilloscope and observe the waveform formed.

References:

  1. The previous blog on experiments using PSLab focusing in electronics https://blog.fossasia.org/electronics-experiments-with-pslab/
  2. The previous blog on experiments using PSLab involving some general experiments https://blog.fossasia.org/fascinating-experiments-with-pslab/
  3. Read more about differentiators and integrators and their uses https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/differentiator-integrator-circuits/
Continue ReadingElectrical Experiments with PSLab
Read more about the article Implementing Skill Listing in SUSI Android App using Nested RecyclerViews

Implementing Skill Listing in SUSI Android App using Nested RecyclerViews

SUSI Skills are rules that are defined in SUSI Skill Data repo which are basically the responses SUSI gives to the user queries. When a user queries something from the SUSI Android app, a query to SUSI Server is made which further fetches response from SUSI Skill Data and gives the response to the app. Similarly, when we need to list all skills, an API call is made to server to list all skills. The server then checks the SUSI Skill Data repo for the skills and then return all the required information to the app. Then the app displays all the information about the skill to user. User then can view details of each skill and then interact on the chat interface to use that skill. This process is similar to what SUSI Skill CMS does. The CMS is a skill wiki like interface to view all skills and then edit them. Though the app can not be currently used to edit the skills but it can be used to view them and try them on the chat interface.

API Information

For listing SUSI Skill groups, we have to call on  /cms/getGroups.json

This will give you all groups in SUSI model in which skills are present. Current response:

{
  "session": {"identity": {
    "type": "host",
    "name": "14.139.194.24",
    "anonymous": true
  }},
  "accepted": true,
  "groups": [
    "Small Talk",
    "Entertainment",
    "Problem Solving",
    "Knowledge",
    "Assistants",
    "Shopping"
  ],
  "message": "Success: Fetched group list"
}

So, the groups object gives all the groups in which SUSI Skills are located.

Next comes, fetching of skills. For that the endpoint is /cms/getGroups.json?group=GROUP_NAME

Since we want all skills to be fetched, we call this api for every group. So, for example we will be calling http://api.susi.ai/cms/getSkillList.json?group=Entertainment for getting all skills in group “Entertainment”. Similarly for other groups as well.

Sample response of skill:

{
  "accepted": true,
  "model": "general",
  "group": "Shopping",
  "language": "en",
  "skills": {"amazon_shopping": {
    "image": "images/amazon_shopping.png",
    "author_url": "https://github.com/meriki",
    "examples": ["Buy a dress"],
    "developer_privacy_policy": null,
    "author": "Y S Ramya",
    "skill_name": "Shop At Amazon",
    "dynamic_content": true,
    "terms_of_use": null,
    "descriptions": "Searches items on Amazon.com for shopping",
    "skill_rating": null
  }},
  "message": "Success: Fetched skill list",
  "session": {"identity": {
    "type": "host",
    "name": "14.139.194.24",
    "anonymous": true
  }}
}

It gives all details about skills:

  1. image
  2. author_url
  3. examples
  4. developer_privacy_policy
  5. author
  6. skill_name
  7. dynamic_content
  8. terms_of_use
  9. descriptions
  10. skill_rating

Implementation in SUSI Android App

Skill Listing UI of Google Assistant

Skill Listing UI of SUSI SKill CMS

Skill Listing UI of SUSI Android App

The UI of skill listing in SUSI Android App is the mixture of UI of Skill listing in Google Assistant ap and SUSI Skill CMS. It displays skills in a beautiful manner with horizontal recyclerview nested in vertical recyclerview.

So, for implementing horizontal recyclerview inside vertical recyclerview, you need two viewholders and two adapters (one each for a recyclerview).

Let’s see the implementation.

1. First task is to fetch the information of groups in which skills are located. This line calls method in SkillListModel which then makes an API call to fetch groups.

skillListingModel.fetchGroups(this)

2. When the API call is succeeded, the below mentioned method is called which then calls a  skillListingModel.fetchSkills(groups[0], this) which fetches the skills located in group[0] group.

override fun onGroupFetchSuccess(response: Response<ListGroupsResponse>) {
   if (response.isSuccessful && response.body() != null) {
       groupsCount = response.body().groups.size
       groups = response.body().groups
       skillListingModel.fetchSkills(groups[0], this)
   } else {
       skillListingView?.visibilityProgressBar(false)
       skillListingView?.displayErrorDialog()
   }
}

3. When API call for fetching skills in group[0] succeeds, the count value is increased and then skills in group[1] are fetched and so on.

override fun onSkillFetchSuccess(response: Response<ListSkillsResponse>, group: String) {
   if (response.isSuccessful && response.body() != null) {
       skills.add(Pair(group, response.body().skillMap))
       count++
       if(count == groupsCount) {
           skillListingView?.visibilityProgressBar(false)
           skillListingView?.updateAdapter(skills)
       } else {
           skillListingModel.fetchSkills(groups[count], this)
       }
   } else {
       skillListingView?.visibilityProgressBar(false)
       skillListingView?.displayErrorDialog()
   }
}

4. When skills in all groups are fetched, the data in adapter is updated using skillGroupAdapter.notifyDataSetChanged()

override fun updateAdapter(skills: ArrayList<Pair<String, Map<String, SkillData>>>) {
   this.skills.clear()
   this.skills.addAll(skills)
   skillGroupAdapter.notifyDataSetChanged()
}

5. The data is set to the layout in two adapters made earlier. The following is the code to set the group name and adapter to horizontal recyclerview. This is the GroupAdapter to set data to row item in vertical recyclerview.

override fun onBindViewHolder(holder: GroupViewHolder?, position: Int) {
   if(skills[position].first != null)
       holder?.groupName?.text = skills[position].first
   holder?.skillList?.setHasFixedSize(true)
   val mLayoutManager = LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false)
   holder?.skillList?.layoutManager = mLayoutManager
   holder?.skillList?.adapter = SkillListAdapter(context, skills[position])
}

6. Similarly, the data of each individual element in the horizontal recyclerview is set in the skillAdapter. The data set are title, examples, description and image. We have used Picasso library to load images from the URL.

override fun onBindViewHolder(holder: SkillViewHolder?, position: Int) {
   val skillData = skillDetails.second.values.toTypedArray()[position]

   if(skillData.skillName == null || skillData.skillName.isEmpty()){
       holder?.skillPreviewTitle?.text = context.getString(R.string.no_skill_name)
   } else {
       holder?.skillPreviewTitle?.text = skillData.skillName
   }

   if( skillData.descriptions == null || skillData.descriptions.isEmpty()){
       holder?.skillPreviewDescription?.text = context.getString(R.string.no_skill_description)
   } else {
       holder?.skillPreviewDescription?.text = skillData.descriptions
   }

   if(skillData.examples == null || skillData.examples.isEmpty())
       holder?.skillPreviewExample?.text = StringBuilder("\"").append("\"")
   else
       holder?.skillPreviewExample?.text = StringBuilder("\"").append(skillData.examples[0]).append("\"")

   if(skillData.image == null || skillData.image.isEmpty()){
       holder?.previewImageView?.setImageResource(R.drawable.ic_susi)
   } else {
       Picasso.with(context.applicationContext).load(StringBuilder(imageLink)
               .append(skillDetails.first.replace(" ","%20")).append("/en/").append(skillData.image).toString())
               .fit().centerCrop()
               .into(holder?.previewImageView)
   }
}

Summary

So, this blog talked about how the Skill Listing feature in SUSI Android App is implemented. This included how a network call is made, logic for making different network calls, making a nested horizontal recyclerview inside vertical recyclerview, etc. So, If you are looking forward to contribute to SUSI Android App, this can help you a little. But if not so, this may also help you in understanding and how you can implement nested recyclerviews similar to Google Play Store.

References

  1. To know about servlets https://en.wikipedia.org/wiki/Java_servlet
  2. To see how to implement one https://www.javatpoint.com/servlet-tutorial
  3. To see how to make network calls in android using Retrofit https://guides.codepath.com/android/Consuming-APIs-with-Retrofit
  4. To see how to implement Horizontal recyclerView inside Vertical recyclerView http://android-pratap.blogspot.in/2015/12/horizontal-recyclerview-in-vertical.html
  5. To see how to implement custom RecyclerView Adapter https://www.survivingwithandroid.com/2016/09/android-recyclerview-tutorial.html
Continue ReadingImplementing Skill Listing in SUSI Android App using Nested RecyclerViews
Read more about the article Enabling Google App Signing for Android Project

Enabling Google App Signing for Android Project

Signing key management of Android Apps is a hectic procedure and can grow out of hand rather quickly for large organizations with several independent projects. We, at FOSSASIA also had to face similar difficulties in management of individual keys by project maintainers and wanted to gather all these Android Projects under singular key management platform:

To handle the complexities and security aspect of the process, this year Google announced App Signing optional program where Google takes your existing key’s encrypted file and stores it on their servers and asks you to create a new upload key which will be used to sign further updates of the app. It takes the certificates of your new upload key and maps it to the managed private key. Now, whenever there is a new upload of the app, it’s signing certificate is matched with the upload key certificate and after verification, the app is signed by the original private key on the server itself and delivered to the user. The advantage comes where you lose your key, its password or it is compromised. Before App Signing program, if your key got lost, you had to launch your app under a new package name, losing your existing user base. With Google managing your key, if you lose your upload key, then the account owner can request Google to reassign a new upload key as the private key is secure on their servers.

There is no difference in the delivered app from the previous one as it is still finally signed by the original private key as it was before, except that Google also optimizes the app by splitting it into multiple APKs according to hardware, demographic and other factors, resulting in a much smaller app! This blog will take you through the steps in how to enable the program for existing and new apps. A bit of a warning though, for security reasons, opting in the program is permanent and once you do it, it is not possible to back out, so think it through before committing.

For existing apps:

First you need to go to the particular app’s detail section and then into Release Management > App Releases. There you would see the Get Started button for App Signing.

The account owner must first agree to its terms and conditions and once it’s done, a page like this will be presented with information about app signing infrastructure at top.

So, as per the instructions, download the PEPK jar file to encrypt your private key. For this process, you need to have your existing private key and its alias and password. It is fine if you don’t know the key password but store password is needed to generate the encrypted file. Then execute this command in the terminal as written in Step 2 of your Play console:

java -jar pepk.jar –keystore={{keystore_path}} –alias={{alias}} –output={{encrypted_file_output_path}} –encryptionkey=eb10fe8f7c7c9df715022017b00c6471f8ba8170b13049a11e6c09ffe3056a104a3bbe4ac5a955f4ba4fe93fc8cef27558a3eb9d2a529a2092761fb833b656cd48b9de6a

You will have to change the bold text inside curly braces to the correct keystore path, alias and the output file path you want respectively.

Note: The encryption key has been same for me for 3 different Play Store accounts, but might be different for you. So please confirm in Play console first

When you execute the command, it will ask you for the keystore password, and once you enter it, the encrypted file will be generated on the path you specified. You can upload it using the button on console.

After this, you’ll need to generate a new upload key. You can do this using several methods listed here, but for demonstration we’ll be using command line to do so:

keytool -genkey -v -keystore {{keystore_path}} -alias {{alias_name}} -keyalg RSA -keysize 2048 -validity 10000

The command will ask you a couple of questions related to the passwords and signing information and then the key will be generated. This will be your public key and be used for further signing of your apps. So keep it and the password secure and handy (even if it is expendable now).

After this step, you need to create a PEM upload certificate for this key, and in order to do so, execute this command:

keytool -export -rfc -keystore {{keystore_path}} -alias {{alias_name}} -file {{upload_certificate.pem}}

After this is executed, it’ll ask you the keystore password, and once you enter it, the PEM file will be generated and you will have to upload it to the Play console.

If everything goes right, your Play console will look something like this:

 

Click enrol and you’re done! Now you can go to App Signing section of the Release Management console and see your app signing and new upload key certificates

 

You can use the SHA1 hash to confirm the keys as to which one corresponds to private and upload if ever in confusion.

For new apps:

For new apps, the process is like a walk in park. You just need to enable the App Signing, and you’ll get an option to continue, opt-out or re-use existing key.

 

If you re-use existing key, the process is finished then and there and an existing key is deployed as the upload key for this app. But if you choose to Continue, then App Signing will be enabled and Google will use an arbitrary key as private key for the app and the first app you upload will get its key registered as the upload key

 

This is the screenshot of the App Signing console when there is no first app uploaded and you can see that it still has an app signing certificate of a key which you did not upload or have access to.

If you want to know more about app signing program, check out these links:

Continue ReadingEnabling Google App Signing for Android Project