Android Widgets – blog.fossasia.org

Implementing Card View in PSLab app

Post author:harsh-2711
Post published:July 31, 2018
Post category:Android FOSSASIA GSoC Pocket Science Lab
Post comments:0 Comments

Card View was announced by Google in I/O ‘14 conference. Although it started a bit slow, but now we can see most of the apps like Snapchat, Google, Facebook, etc. using this widget. So, this blog is solely contributed on how to implement Card View in your own app by taking example of PSLab application.

What is Card View ?

CardView is a view container or ViewGroup that inherits its nature from FrameLayout which further inherits from ViewGroup itself. The only thing that separates a CardView from any other ViewGroups is its nature to behave like a card, more specifically the shadow and rounded corners. The basic customization that a CardView provides includes CornerRadius, Elevation, MaxElevation, ContentPadding, CompatPadding, PreventCornerOverlap, and a dedicated CardBackgroundColor or say Card Background which is the most necessary feature for a card to look cool.

Step by Step description how CardView was implemented in PSLab

First step is to add dependencies in your project as widgets like Card View, Recyclerview, etc. are not included in a common repository of widgets provided by Google.

App level dependency :

compile 'com.android.support:cardview-v7:26.0.0'

compile 'com.android.support:recyclerview-v7:+'

If you are using Android Studio 3.0+ than add the following dependency instead of above :

implementation 'com.android.support:cardview-v7:26.0.0'

implementation 'com.android.support:recyclerview-v7:27.1.1'

Now we can use Card View widget in our app. So, first make add card view in layout section like this :

<android.support.v7.widget.CardView
    	android:id="@+id/card_view"
    	android:layout_width="match_parent"
    	android:layout_height="@dimen/total_height_card"
    	android:layout_gravity="center"
    	android:layout_margin="@dimen/card_margin"
    	card_view:cardCornerRadius="@dimen/card_radius">
 </android.support.v7.widget.CardView>

These are the basic attributes that are used while declaring a card view. Other possible attributes can be :

Elevation – Used to elevate card to give a depth effect
MaxElevation – Used to give constraint to the depth effect
ContentPadding – Used to provide padding between content and the card
PreventCornerOverlap – To prevent different corners to overlap as shown in figure 1.

Figure 1. Image showing corner overlapping in CardView

Now to set the objects inside the Card View, mostly RelativeLayout is preferred as it gives the freedom to place objects in reference of others whereas LinearLayout provides freedom to place them in only one direction. Other layouts such as FrameLayout, Tables, etc. can be used as per the need of the app.
Now we will create a layout that will hold all the cards using RecyclerView.

<android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

Now after setting the layouts, it’s time to make adapter which inflates the information in the cards which is then represented using RecyclerView.

public class ApplicationAdapter extends RecyclerView.Adapter<ApplicationAdapter.Holder> {

	private List<ApplicationItem> applicationList;
	private final OnItemClickListener listener;
	/**
 	* View holder for application list item
 	*/
	public class Holder extends RecyclerView.ViewHolder {

    	TextView header, description;
    	ImageView applicationIcon; //Background Image

    	public Holder(View itemView) {
        super(itemView);
        this.header = itemView.findViewById(R.id.heading_card);
        this.description = itemView.findViewById(R.id.description_card);
        this.applicationIcon = itemView.findViewById(R.id.application_icon);
    	}

    	public void setup(final ApplicationItem applicationItem, final OnItemClickListener listener) {
      header.setText(applicationItem.getApplicationName());
      description.setText(applicationItem.getApplicationDescription());
      applicationIcon.setImageResource(applicationItem.getApplicationIcon());
         }
	}

	public ApplicationAdapter(Context mContext, List<ApplicationItem> applicationList, OnItemClickListener listener) {
    	this.mContext = mContext;
    	this.applicationList = applicationList;
    	this.listener = listener;
	}

     @Override
	public Holder onCreateViewHolder(ViewGroup parent, int viewType) {
    	View itemView = LayoutInflater.from(parent.getContext())
            	.inflate(R.layout.application_list_item, parent, false);
    	return new Holder(itemView);
	}

Following is the detailed explanation of each and every method :

Holder(View ) – As name suggests, it holds all the items that are included in a single card together
setup() – This method can contain any number of parameters as per requirement. It basically sets the data in the views in the card
ApplicationAdapter() – Constructor
onCreateViewHolder() – It inflates the layout containing CardView as soon as the data gets ready to be fed in it

Now as adapter is ready, we can declare RecyclerView in Java code to implement CardView. The main reason to use RecyclerView is that it provides the feature of scrollability so that a number of cards can be adjusted on the screen. ScrollView can also be used but it slows down the app as it tries to load all the card at once rather than loading cards as per use like RecyclerView.

RecyclerView listView = view.findViewById(R.id.applications_recycler_view);
    	RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(context, rows);
    	listView.setLayoutManager(mLayoutManager);
    	listView.setItemAnimator(new DefaultItemAnimator());
    	listView.setAdapter(applicationAdapter);

Here, we have used GridLayoutManager to use grids along with RecyclerView. It is optional and can be used as per requirement. Also, before setting adapter, fill the adapter with relevant data or else no card will be seen in actual app.

Now the app is ready to be built and tested on mobile device. This is how it looks in the PSLab application after implementing the above guide :

Figure 2. Screenshot of CardView implemented in PSLab app

So, in this way great user experience can be given by using this very basic widget. But great attention should be given while designing the objects inside the card as the selection and position of the objects is what makes the card look good. Objects used in making cards for PSLab very well suited the app and so are designed like that. Practice should be done by taking reference of some very good apps like Snapchat, Google, etc. and from Material Designs provided by Google before implementing them in actual project.

Resources

https://www.androidhive.info/2016/05/android-working-with-card-view-and-recycler-view/ – This article gives a better practice by implementing a real world example
https://developer.android.com/reference/android/support/v7/widget/CardView – Official documentation by Google on CardView
https://developer.android.com/guide/topics/ui/layout/recyclerview – Official documentation by Google on RecyclerView

Creating a Widget for your Android App

Post author:the-dagger
Post published:July 30, 2016
Post category:Android App generator FOSSASIA GSoC Open Event Tutorial

Having a widget for your app, not only helps it to stand out among its alternatives but also provides user information on the go without having to open the app. Keeping this thought in mind, I decided to make a widget for my GSoC project. Let’s go through the steps involved.

Step 1:

Creating a new widget from Android Studio.

Open up your project for which you need a widget and navigate to the project’s Java source. Create a new sub-package there named widget. Right click on the newly created sub-package and select the New->Widget option from there.

Follow the instructions on the next screen.

Just kidding, this was the easy part, off to more harder things now!

Step 2:

Populating the widget with data.

Now, there can be 2 broad type of widgets Information Widgets and Collection Widgets.

Information widgets are simple widgets that are used to display an information that changes with time, for example Weather Widget or a Clock Widget.

Whereas, collection widgets are widgets which display a collection of data, for example the GMail widget is a collection widget.
These are relatively complex and harder than the Information Widgets.

In this post, we will focus on making a Collection Widget.

For Collection widgets, we need two layout files, one for the widget and one for each item in the widget collection.

Go ahead and create the two layout files. The wizard automatically generates the widget_layout.xml for you, you just need to edit it up.

stock_layout.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:id="@+id/widget_toolbar"
        android:layout_height="?android:attr/actionBarSize"
        android:background="@color/colorPrimary">

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:src="@drawable/stock_up"
            android:contentDescription="@string/stock_widget" />

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:src="@drawable/stock_down"
            android:contentDescription="@string/stock_widget" />

        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginStart="32dp"
            android:gravity="center_vertical"
            android:text="@string/your_stocks"
            android:textAppearance="@android:style/TextAppearance.DeviceDefault.Widget.ActionBar.Title"
            android:layout_marginLeft="32dp" />
    </LinearLayout>

    <ListView
        android:id="@+id/widget_listView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/backGround"></ListView>

</LinearLayout>

list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="72dp"
    android:gravity="center_vertical"
    android:orientation="horizontal"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    >
  <TextView
      android:id="@+id/stock_symbol"
      style="@style/StockSymbolTextStyle"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:gravity="start|center_vertical"
      tools:text="List Item"
      />
</LinearLayout>

Next up, having a look at the modified files, we can see that the Widget creation wizard added some stuff into out AndroidManifest.xml and created a new java file.

Upon taking a closer look at the manifest, we can see that the widget’s java class has been registered as a <receiver/>

Next, opening up the NewAppWidget.java, we will see that it extends AppWidgetProvider and some methods are already overridden for you.

Time to edit up this file to reference to the layouts we have just created.

import android.annotation.TargetApi;
import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.support.annotation.NonNull;
import android.widget.RemoteViews;

/**
 * Implementation of App Widget functionality.
 */
public class StockWidgetProvider extends AppWidgetProvider {

    private static void updateAppWidget(Context context, AppWidgetManager appWidgetManager,
                                        int appWidgetId) {
        // Construct the RemoteViews object which defines the view of out widget
        RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.widget_layout);
        // Instruct the widget manager to update the widget
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
            setRemoteAdapter(context, views);
        } else {
            setRemoteAdapterV11(context, views);
        }
        /** PendingIntent to launch the MainActivity when the widget was clicked **/
        Intent launchMain = new Intent(context, MainActivity.class);
        PendingIntent pendingMainIntent = PendingIntent.getActivity(context, 0, launchMain, 0);
        views.setOnClickPendingIntent(R.id.widget, pendingMainIntent);
        appWidgetManager.notifyAppWidgetViewDataChanged(appWidgetId,R.id.widget_listView);
        appWidgetManager.updateAppWidget(appWidgetId, views);
    }

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        // There may be multiple widgets active, so update all of them
        for (int appWidgetId : appWidgetIds) {
            updateAppWidget(context, appWidgetManager, appWidgetId);
        }

        super.onUpdate(context, appWidgetManager, appWidgetIds);
    }

    @Override
    public void onEnabled(Context context) {
        // Enter relevant functionality for when the first widget is created
    }

    @Override
    public void onDisabled(Context context) {
        // Enter relevant functionality for when the last widget is disabled
    }

  /** Set the Adapter for out widget **/

    @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    private static void setRemoteAdapter(Context context, @NonNull final RemoteViews views) {
        views.setRemoteAdapter(R.id.widget_listView,
                new Intent(context, StockWidgetService.class));
    }

    
    /** Deprecated method, don't create this if you are not planning to support devices below 4.0 **/
    @SuppressWarnings("deprecation")
    private static void setRemoteAdapterV11(Context context, @NonNull final RemoteViews views) {
        views.setRemoteAdapter(0, R.id.widget_listView,
                new Intent(context, StockWidgetService.class));
    }

}

Now, create a WidgetDataProvider which will provide us with data to be displayed inside the widget.

You can use a static data for now (like a prefilled ArrayList, but make sure that this data should be dynamic for making the widget meaningful)

import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.os.Binder;
import android.widget.RemoteViews;
import android.widget.RemoteViewsService;

/**
 * Created by the-dagger on 24/7/16.
 */

public class WidgetDataProvider implements RemoteViewsService.RemoteViewsFactory {

    private Context context;
    private Cursor cursor;
    private Intent intent;

    //For obtaining the activity's context and intent
    public WidgetDataProvider(Context context, Intent intent) {
        this.context = context;
        this.intent = intent;
    }

    private void initCursor(){
        if (cursor != null) {
            cursor.close();
        }
        final long identityToken = Binder.clearCallingIdentity();    
        /**This is done because the widget runs as a separate thread 
        when compared to the current app and hence the app's data won't be accessible to it
        because I'm using a content provided **/
        cursor = context.getContentResolver().query(QuoteProvider.Quotes.CONTENT_URI,
                new String[]{QuoteColumns._ID, QuoteColumns.SYMBOL, QuoteColumns.BIDPRICE,
                        QuoteColumns.PERCENT_CHANGE, QuoteColumns.CHANGE, QuoteColumns.ISUP},
                QuoteColumns.ISCURRENT + " = ?",
                new String[]{"1"},null);
        Binder.restoreCallingIdentity(identityToken);
    }

    @Override
    public void onCreate() {
        initCursor();
        if (cursor != null) {
            cursor.moveToFirst();
        }
    }

    @Override
    public void onDataSetChanged() {
        /** Listen for data changes and initialize the cursor again **/
        initCursor();
    }

    @Override
    public void onDestroy() {
    cursor.close();
    }

    @Override
    public int getCount() {
        return cursor.getCount();
    }

    @Override
    public RemoteViews getViewAt(int i) {
        /** Populate your widget's single list item **/
        RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.list_item_quote);
        cursor.moveToPosition(i);
        remoteViews.setTextViewText(R.id.stock_symbol,cursor.getString(cursor.getColumnIndex(QuoteColumns.SYMBOL)));
        remoteViews.setTextViewText(R.id.bid_price,cursor.getString(cursor.getColumnIndex(QuoteColumns.BIDPRICE)));
        remoteViews.setTextViewText(R.id.change,cursor.getString(cursor.getColumnIndex(QuoteColumns.CHANGE)));
        if (cursor.getString(cursor.getColumnIndex(QuoteColumns.ISUP)).equals("1")) {
            remoteViews.setInt(R.id.change, "setBackgroundResource", R.drawable.percent_change_pill_green);
        } else {
            remoteViews.setInt(R.id.change, "setBackgroundResource", R.drawable.percent_change_pill_red);
        }
        return remoteViews;
    }

    @Override
    public RemoteViews getLoadingView() {
        return null;
    }

    @Override
    public int getViewTypeCount() {
        return 1;
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }
}

Let’s also create a service that invokes the WidgetDataProvider after a fixed interval

import android.content.Intent;
import android.widget.RemoteViewsService;

/**
 * Created by the-dagger on 24/7/16.
 */

public class StockWidgetService extends RemoteViewsService {
    @Override
    public RemoteViewsFactory onGetViewFactory(Intent intent) {
        return new WidgetDataProvider(this,intent);
    }
}

Phew.. almost done with this now.

Finally edit up the widget_info.xml located inside /res/values/xml/ of your project.

Edit it to reference the time after which your widget will be updated, the preview image which should show up in the widget picker and minimum width and height of the widget.

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialKeyguardLayout="@layout/app_widget"
    android:initialLayout="@layout/app_widget"
    android:minHeight="110dp"
    android:minWidth="170dp"
    android:previewImage="@drawable/example_appwidget_preview"
    android:resizeMode="horizontal|vertical"
    android:updatePeriodMillis="86400000"
    android:widgetCategory="home_screen"></appwidget-provider>

Well, once this is done, go ahead and fire up your app. You will be able to see the newly created and updated widget in your homescreen.

Pretty awesome right!
Congratulations on making your first widget.

For now the app only opens a specific activity on clicking it, but you can read up a bit on how to execute a separate task on clicking each item on the list by using a pendingIntent.