Saving Sensor Data in CSV format

PSLab Android app by FOSSASIA provides a variety of features to its users. One of them is accessing various types of sensors both built into mobile phone and external sensors connected with PSLab device. In earlier versions users were only able to view the captured data. Moving forward, adding improvements to the app, now there is a feature to save those data displayed in graphs in csv format.

This feature is important in many ways. One is educational. In a classroom, teachers can ask students to perform an experiment and prepare a report using the data collected. By just visualizing they cannot do this. Actual data points must be made available. Another use is sharing data sets related to say environmental data over different demographics.

CSV, or comma-separated values file is a text file where stored data are separated by commas. The file stores these tabular data (numbers and text) in plain text format. Each line of the file represents a data record. Each data record consists of one or more fields, separated by commas. CSV files are commonly used to store sensor data because of its easy use. This post is about how PSLab device uses CSV file to write sensor data in it.

In PSLab android source code, there is a dedicated class to handle read sensor data from different instruments called “CSVLogger”. Developers can easily instantiate this class wherever they want a data logging as follows;

CSVLogger logger = new CSVLogger(<SUBFOLDER>); 
logger .writeCSVFile("Heading1,Heading2,Heading3\n");

This will create a blank folder in “PSLab” folder in device storage.  The CSV file is generated with the following convention according to the date and time where data is saved in the file.


A sample file would have a name like 20180710-07:30:28.csv inside the SUBFOLDER which is specific to each instrument. Folder name will be the one used when initiating the CSVLogger.

With this method, logging data is pretty easy. Simply create a string which is a comma seperated and ended with a new line character. Then simply call the writeCSVFile(data) method with the string as a parameter added to it. It will keep appending string data until a new file is created. File creation can be handled by developers at their own interests and preferences.

String data = String.valueOf(System.currentTimeMillis()) + "," + item.getX() + "," + item.getY() + "\n";


To bring out an example let’s view how it’s implemented in Lux Meter instrument. This is a good source one can refer to when adding this feature in fragments

inside a main activity. In Lux Meter, there is the parent activity named Lux Meter and inside that there are two fragments, one is fragmentdata and the other one is fragmentsettings. Data capturing and saving occurs inside fragmentdata.

Menu icon controlling happens in the parent activity and we have bound a variable across the main activity and child fragment as follows;

LuxMeterActivity parent = (LuxMeterActivity) getActivity();
if (parent.saveData) {/* Save Data */}

This makes it easier listening menu icon clicks and start/stop recording accordingly. How to handle menu icons is beyond the scope of this blog and you can find tutorials on how to do that in the Resources section at the bottom of this blog post.

Once these CSV files are available, users can easily integrate them with advanced software like Matlab or Octave to do further analysis and processing to captured data sets.


  1. CSV Logger:
  2. Android Menu options:

Displaying all the images from storage at once in Phimpme Android Application

In the Phimpme Android application, the images are displayed in the albums in which they are indexed in the device’s storage. However, there is also an “All photos” section in the application where all the images present in the device’s storage are displayed at once irrespective of the folder they’re indexed in. So in this post, I will be discussing how we achieved the “All Photos”  functionality.

Android framework provides developers with a media content provider class called MediaStore. It contains metadata for all available media on both internal and external storage devices. With the help of particular methods we can obtain metadata for all the images stored in the device’s storage.

Step 1

So First we need to get the Uri from MediaStore content provider pointing to the media(here media refers to the photos stored on the device). This can be done by the following snippet of code.

Uri uri = android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI;

Step 2

Now retrieving a cursor object containing the data column for the image media is required to be performed. The data column will contain the path to the particular image files on the disk. This can be done by querying the MediaColumns table of the MediaStore class, which can be performed by the use of the content resolver query method. The mentioned functionality can be achieved by the following lines of code.

String[] projection = {MediaStore.MediaColumns.DATA};
Cursor cursor = activity.getContentResolver().query(uri, projection, null, null, null);

Step 3

In the final step, we would retrieve the path of all the images by iterating through the cursor object obtained in the previous step and keep adding those paths to an ArrayList<String>. Creating Media objects passing in the image path and concurrently adding those Media objects to an ArrayList<Media> to be done thereafter. Finally, the dataset(ArrayList<Media> in this case) containing Media objects for all the images is required to be passed to the Media Adapter in order to display all the photos in the UI. The code snippets used for the final steps are provided below.

while (cursor.moveToNext()) {
  absolutePathOfImage = cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.MediaColumns.DATA));
ArrayList<Media> list = new ArrayList<>();

for (String path : listOfAllImages) {
  list.add(new Media(new File(path)));
return list;

This is how we achieved the functionality to display all the images from the storage on a single screen(at once) in the Phimpme Android application. To get the full source code, please refer to the Phimpme Android Github repository listed in the resource section below.

The screenshot for displaying the “All photos” section is provided below.


1.Android Developer Guide –

2.Github-Phimpme Android Repository –

3.Displaying all the images from gallery in android –

Use PreferenceManager in place of SharedPreferences

SharedPreferences is used in android to store data in the form of a key-value pair in an application. But, sometimes we need to store data at many places in the application such as saving the login email or a particular information that remains the same for the entire use of the app. In SUSI.AI android app class is made that uses the sharedpreferences in android and provides a custom wrapper that is used to store the data in the key-value pair form in the app.

To store data in sharedpreferences through the PreferenceManager class we just need to declare an instance of the PreferenceManager in the location in which we want to save the data. The SUSI.AI Android app opens up the login screen and on just viewing the welcome cards for the first time due to the incorrect implementation of the sharedpreferences, using the Preference Manager we can correctly implement the preferences in welcome activity.

Whenever we install the SUSI.AI Android app, on opening it for the first time we see welcome cards that give a basic overview of the app. So, now after swiping all the cards and on reaching the final card instead of clicking GOT IT to move to the login screen and on pressing the home button we put the app in the background. Now, what happened was when the app showed cards, it was due to the activity.

In the onCreate() method of this activity we check whether the WelcomeActivity is opened for the first time or not. In this case we make use of the class.

if (PrefManager.getBoolean(“activity_executed”, false)) {
  Intent intent = new Intent(this, LoginActivity.class);
} else {
  PrefManager.putBoolean(“activity_executed”, true);

This piece of code calls the getBoolean(<preferenceKey>,<preferenceDefaultValue>) of the class and checks the boolean value against the preference key passed in the function.

If it is the first time when this function is called then the default value is accessed against the preference key: “activity_executed”, which is passed as false and no code within the if statement is executed and so the code in the else block is executed which puts the value true as the preference value against the key “activity_executed” and the next line is executed in the sequence after this line. In short, on opening the app for the first time the preference key “activity_executed” has a value of true against it.

When we close the app by destroying it while it is in the WelcomeActivity, the onDestroy() method is called and memory is cleared, but when we open the app again we expect to see the Welcome Cards, but instead we find that we are on the login screen, even though the GOT IT button on the final card was not pressed. This is because when we go through the onCreate() method again the if condition is true this time and it sends the user directly to the Login activity.

To, solve this problem the method that was followed was :

  1. Remove the else condition in the if condition where we check the value stored against the key “activity_executed” key.
  2. In the onCreate() method of the LoginActivity.kt file use the PrefManager class to put a boolean value equal to true against the key : “activity_executed”.So the code added in the LoginActivity.kt file’s onCreate() method was :
PrefManager.putBoolean(“activity_executed”, true)

Also, the else condition was removed in the Welcome activity. Now, with these changes in place unless we click GOT IT on the final card in the welcome activity we won’t be able to go to the Login Activity, and since we won’t be able to go to the final activity the value against the key “activity_executed” will be false. Also, once we move to the login activity we will not be able to see the cards as the if condition described above will be true and the intent will fire the user to the Login Activity forever.

Therefore, using the PrefManager class it became very easy to put values or get values stored in the sharedpreferences in android. The methods are created in the Preference manager for different types corresponding to the different return types present that can be used to store the values allowed by the SharedPreferences in Android.

Using the PrefManager class functions it was made easy in SUSI.AI android app to access the SharedPreferences and using it a flaw in the auth flow and opening of the app was resolved.



  1. How to launch an activity only once for the first time! – Divya Jain:
  2. Save key-value data : ttps://
  3. PrefManager Class:

Chrome Custom Tabs Integration – SUSI.AI Android App

Earlier, we have seen the apps having external links that opens and navigates the user to the phone browser when clicked, then we came up with something called WebView for Android, but nowadays we have shifted to something called In-App browsers. The main drawback of the system/ phone browsers are they caused heavy transition. To overcome this drawback “Chrome Custom Tabs” were invented which allowed users to walk through the web content seamlessly.

SUSI.AI Android App earlier used the system browser to open any link present in the app.

This can be implemented easily by

Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));

This lead to a huge transition between the context of the app and the web browser.

Then, to reduce all the clutter Chrome Custom tabs by Google was evolved which drastically increased the loading speed and the heavy context switch was also not taking place due to the integration and adaptability of custom tabs within the app.

Chrome custom tabs also are very secured like Chrome Browser and uses the same feature and give developers a more control on the custom actions, user interface within the app.

                                comparing the load time of the above mentioned techniques

Ref : Android Dev – Chrome Custom Tabs

Integration of Chrome Custom Tabs

  • Adding the dependency in build.gradle(app-level) in the project
dependencies {
    //Other dependencies 
    compile ''
  • Now instantiating a CustomTabsIntent Builder

    String url = “” // can be any link
    CustomTabsIntent.Builder builder = new CustomTabsIntent.Builder(); //custom tabs intent builder
    CustomTabsIntent customTabsIntent =;
  • We can also add animation or customize the color of the toolbar or add action buttons.

    builder.setColor(Color.RED) //for setting the color of the toolbar 
    builder.setStartAnimations(this, R.anim.slide_in_right, R.anim.slide_out_left); //for start animation
    builder.setExitAnimations(this, R.anim.slide_in_left, R.anim.slide_out_right); //for exit animation
  • Finally, we have have achieved everything with a little code. Final launch the web page

    Uri webpage = Uri.parse(url); //We have to pass an URI
    customTabsIntent.launchUrl(context, webpage); //launching through custom tabs

Benefits of Chrome Custom Tabs

  1. UI Customization are easily available and can be implemented with very few lines of code. 
  2. Faster page loading and in-app access of the external link 
  3. Animations for start/exit  
  4. Has security and uses the same permission model as in chrome browser.


  1. Chrome Custom Tabs:
  2. Chrome Custom Tabs Github Repo: GitHub – GoogleChrome/custom-tabs-client: Chrome custom tabs
  3. Android Blog: Android Developers Blog: Chrome custom tabs smooth the transition
  4. Video: Chrome Custom Tabs: Displaying 3rd party content in your Android


Building PSLab Android app with Fdroid

Fdroid is a place for open source enthusiasts and developers to host their Free and Open Source Software (FOSS) for free and get more people onboard into their community. Hosting an app in Fdroid is not a fairly easy process just like hosting one in Google Play. We need to perform a set of build checks prior to making a merge request (which is similar to pull request in GitHub) in the fdroid-data GitLab repository. PSLab Android app by FOSSASIA has undergone through all these checks and tests and now ready to be published.

Setting up the fdroid-server and fdroid-data repositories is one thing. Building our app using the tools provided by fdroid is another thing. It will involve quite a few steps to get started. Fdroid requires all the apps need to be built using:

$ fdroid build -v -l org.fossasia.pslab


This will output a set of logs which tell us what went wrong in the builds. The usual one in a first time app is obviously the build is not taking place at all. The reason is our metadata file needs to be changed to initiate a build.

    commit=<commit which has the build mentioned in versioncode>


When a metadata file is initially created, this build is disabled by default and commit is set to “?”. We need to fill in those blanks. Once completed, it will look like the snippet above. There can be many blocks of “Build” can be added to the end of metadata file as we are advancing and upgrading through the app. As an example, the latest PSLab Android app has the following metadata “Build” block:



In case of an update, add another “Build” block and mention the version you want to appear on the Fdroid repository as follows:

Auto Update Mode:Version v%v
Update Check Mode:Tags
Current Version:1.1.5
Current Version Code:7


Once it is all filled, run the build command once again. If you have properly set the environment in your local PC, build will end successfully assuming there were no Java or any other language syntax errors.

It is worth to mention few other facts which are common to Android software projects. Usually the source code is packed in a folder named “app” inside the repository and this is the common scenario if Android Studio builds up the project from scratch. If this “app” folder is one level below the root, that is “android/app”, the build instructions shown above will throw an error as it cannot find the project files.

The reason behind this is we have mentioned “subdir=app” in the metadata file. Change this to “subdir=android/app” and run the build again. The idea is to direct the build to find where the project files are.

Apart from that, the commit can be represented by a tag instead of a long commit hash. As an example, if we had merge commits in PSLab labeled as “v.<versioncode>”, we can simply use “commit=v.1.1.5” instead of the hash code. It is just a matter of readability.

Happy Coding!


  1. Metadata :
  2. PSLab Android app Fdroid :

Handling Click Events using Custom Binding Adapters

The Open Event Organiser Android App is the Event management app for organizers using the Open Event Platform. It is currently released in the Alpha phase on the Google Play Store here and is being actively developed by the community.

The Data Binding Library is one of the most popular libraries among the android developers. We use it extensively in the application in order to greatly simplify the UI binding logic. While trying to show the details of a speaker in the application, we wanted to list his/her social media links using Image buttons.

Upon clicking one of these buttons, the user was supposed to be directed to the link after opening the default web browser. This blog post discusses how we used custom Binding Adapters to handle click events on an Image Button by defining a custom attribute.

Defining the Binding Adapter

We defined a simple Binding Adapter for an Image button meant to handle social media links. We used “imageOnClick” as the custom attribute name for specifying the URL that will be opened once the button is clicked.

public static void bindOnImageButtonClickListener(ImageButton imageButton, String url) {
  imageButton.setOnClickListener(view -> {
    if (url != null) {
      Context context = imageButton.getContext();
      Intent intent = new Intent(Intent.ACTION_VIEW);
      if (intent.resolveActivity(context.getPackageManager()) != null) {
      } else {
        Toast.makeText(context, "No Web browser found", Toast.LENGTH_SHORT).show();


The method can be named anything you want and can be placed anywhere in the project but we would recommend creating a separate class for all the Binding adapters.
The important things to take away from the above method are:

  • The method needs to be public otherwise the Data binding framework won’t be able to find it.
  • We need to pass in the view as the first parameter and the attribute value as the second parameter.

Then we simply set the familiar click listener to handle the click interaction. We use the Context from the view passed in the method as the first parameter. Then we create an Intent and set the passed in URL as the data. We make sure that the user has a browser installed on his/her android phone before we try to open the browser. We show a suitable error message if they don’t.

Using it in Layout

Using the custom attribute in the layout was extremely simple. We specified the url using the attribute “imageOnClick” and the rest was handled by the Binding Adapter and the Data binding framework.  

     app:imageOnClick="@{ speaker.linkedin }"
     android:visibility="@{ (speaker.linkedin != null) ? View.VISIBLE : View.GONE }"


Implementing Filters in Android App

Image filters in android app are implemented using the OpenCV library that enables the android developers to write code in C++/C which is compatible with java. I have implemented around eight filters in the filters.cpp file, mainly dealing with the colour variations that took place between the images.

Suppose that the color model used in consideration is the RGB (Red,Green,Blue) model and we define that every pixel is defined using these values. If we simply want to boost or focus on the red part of the image it can be done by enhancing the particular color in the source image i.e. modifying each pixel of the app by enhancing the blue color of each pixel. The code for the same can be written as :

void applyBlueBoostEffect(cv::Mat &src, cv::Mat &dst, int val) {
register int x, y;
float opacity = val * 0.01f;
cvtColor(src, src, CV_BGRA2BGR);
dst = Mat::zeros(src.size(), src.type());
uchar r, g, b,val1;

for (y = 0; y < src.rows; y++) {
for (x = 0; x < src.cols; x++) {
r =<Vec3b>(y, x)[0];
g =<Vec3b>(y, x)[1];
b =<Vec3b>(y, x)[2];
val1 = saturate_cast<uchar>(b*(1+opacity));
if(val1 > 255) {
val1 = 255;
}<Vec3b>(y, x)[0] =
saturate_cast<uchar>(r);<Vec3b>(y, x)[1] =
saturate_cast<uchar>(g);<Vec3b>(y, x)[2] =

In the above function what we are doing is taking the source image and converting it to a matrix of known number of rows and columns. Now, we loop over this matrix created and at each

position in the matrix calculate the red, green and blue values present there. There is a parameterized value “val” that determines the amount to which the color chosen is enhanced.

A simple variable val1 contains the enhanced value of the color chosen, here which is color blue. We modify and boost the color by the equation  :

B = B*(1 + (0.01f* val) )

Finally at this particular position in the matrix all the three values of the color are updated i.e. the original red and green color but the modified blue color.

The output of this filter converts images as below shown :

Before                                                                                   After


In the above method defined we instead of enhancing one color we can even modify two colors or all the three at the same time to get different effects as per the required needs. An example where I implemented a filter to enhance two colors at the same time is given below, the purpose of this filter is to add a violet color tone in the image.

The code for the filter is :

void applyRedBlueEffect(cv::Mat &src, cv::Mat &dst, int val) {
register int x, y;
float opacity = val * 0.01f;
cvtColor(src, src, CV_BGRA2BGR);
dst = Mat::zeros(src.size(), src.type());
uchar r, g, b;
uchar val1,val3;

for (y = 0; y < src.rows; y++) {
for (x = 0; x < src.cols; x++) {
r =<Vec3b>(y, x)[0];
g =<Vec3b>(y, x)[1];
b =<Vec3b>(y, x)[2];
val1 = saturate_cast<uchar>(r*(1+opacity));
if(val1 > 255) {
val1 = 255;

val3 = saturate_cast<uchar>(b*(1+opacity));
if(val3 > 255) {
val3 = 255;
}<Vec3b>(y, x)[0] =
saturate_cast<uchar>(val1);<Vec3b>(y, x)[1] =
saturate_cast<uchar>(g);<Vec3b>(y, x)[2] =


Here we can easily see that there are two values that are updated at the same time i.e. the red and the blue part. The resultant image in that case will have two color values updated and enhanced.

Similarly, instead of two we can also update all the three colors to get uniform enhancement across each color and the resultant image to have all the three colors with a boost effect overall.

The output that we get after the filter that boosts the red and blue colors of an image is  :




Option to secure particular albums in Phimpme Android Application

In the Phimpme Android application, users can perform various operations on the albums available such as creating a zip file of the album, rename an album and many more. However, one another useful functionality that has been added to the Phimpme Android application is the option to secure particular albums. So in this post, I will be discussing the implementation of this security feature.

Step 1

Firstly, a view item for providing the option to enable security for particular albums is required to be added to the security settings layout. The two-state toggle switch widget provided by the Android framework along with a textview has been added as the required view item. A screenshot depicting the layout change is provided below.

The code snippet representing the operation is provided below.

  android:textSize=“@dimen/medium_text” />

  android:hapticFeedbackEnabled=“true” />

Step 2

Now we need to keep track of the albums selected by the user to secure. This can be done by storing the selected album/albums paths in an ArrayList<String> which can be referred later when required in the process.

The required code snippet to perform the above mentioned operation is provided below.

holder.foldercheckbox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
@Override public void onCheckedChanged(CompoundButton compoundButton, boolean b) {

Step 3

Now we need to store the selected albums preference in the SharedPreference so that the user’s security preference persists even when the user exits the application and the user doesn’t have to redo the securing operation the next time user launches the application. The ArrayList<String> object containing the path of the user choice albums are converted to JSON representation by the use of the Gson Java library and the string key denoting the JSON representation of the list is saved in the SharedPreference thereafter.

  SharedPreferences.Editor editor = SP.getEditor();
  Gson gson = new Gson();
  String securedfolders = gson.toJson(securedfol);
  editor.putString(getString(R.string.preference_use_password_secured_local_folders), securedfolders);

Now at the time of performing other operations on the secured folders, the list containing the secured folder paths is retrieved from SharedPreference and the choosen folder’s path is searched in the obtained list, then the user is asked to authenticate accordingly.

This is how we have implemented the functionality to secure particular albums in the Phimpme Android application. To get the full source code, please refer to the Phimpme Android Github repository listed in the resource section below.


1.Android Developer Guide –

2.Github-Phimpme Android Repository –

3.Gson Java library tutorial –

Implementing Search Functionality in Phimpme Android Application.

In the Phimpme Android application, users are provided with options to perform various operations on the albums available such as move, creating a zip file of the album, rename an album and many more. However, one another useful functionality that has been added to the Phimpme Android application is the option to search albums. So in this post, I will be discussing the implementation of search functionality.

Step 1

Android framework provides developers with a search widget called SearchView that provides a user interface for the user to search a query and submit the request. So first setting up the widget in the action bar of the activity is required. The searchview widget can be added to the action bar as a menu item by adding the following lines in the XML menu resource file menu_albums.xml.

  app:showAsAction=“always” />

Step 2

Now SearchView.OnQueryTextListener interface is used for initiating the search operation and listening to the callbacks for changes to the query text. For the purpose of listening to the querytext, two methods are used here both of which are listed below.

onQueryTextChanged(String Text) – This method is called every time the query text is changed by the user and returns a boolean value, false if SearchView should perform the default action of showing any suggestions and true if the action was handled by the listener.

onQueryTextSubmit(String query) – This method is called when the user submits a query which could be done with a key press on the keyboard or by pressing the submit button. It also returns a boolean value which is true if the query has been handled by the listener, otherwise false.

The code snippet for the implementation of the above mentioned interface is provided below.

searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
  public boolean onQueryTextSubmit(String query) {
      return false;

  public boolean onQueryTextChange(String newText) {
      return searchTitle(newText);

Step 3

In the final step, with the use of the onQueryTextChange method of the SearchView.onQueryTextListener interface the search operation and displaying the search results in the UI can be achieved. The onQueryTextChange method is called every time the search-query text changes. From the onQueryTextChange method, another method named searchTitle is invoked. Inside the searchTitle method the album names matching the search-query are searched from an Arraylist<Albums> containing all the albums displayed in the application. The albums obtained as a result of the search operation are then stored in another Arraylist<Album> which is thereafter passed as a parameter to the swapDataSet method of the AlbumsAdapter class to display the searched albums in the album view. The code snippet used for the above operations is provided below.

public boolean searchTitle(String newText) {
  if (!fromOnClick) {
      String queryText = newText;
      queryText = queryText.toLowerCase();
      final ArrayList<Album> newList = new ArrayList<>();
      for (Album album : albList) {
          String name = album.getName().toLowerCase();
          if (name.contains(queryText)) {
          if(textView.getVisibility() == View.VISIBLE){
  } else {
      fromOnClick = false;
  return true;

This is how we have implemented the search functionality in the Phimpme Android application. To get the full source code, please refer to the Phimpme Android Github repository.

The screenshot for displaying the search result in album view is provided below.


1.Android Developer Guide –

2.Github-Phimpme Android Repository –

3.Creating a search interface in Android –