Android (Home screen) Widget - Part 2: Broadcast Widget

    Through Part 1, you've learned some basic knowledge about widget in Android development and the way to make a simple one. In this post, I would like to present a widget can update it's information when clicked (every click on the widget will send a broadcast and show current time at the TextView).

    You have learned all steps of widget creation. We will not be repeating these steps, but now, please pay attention at RemoteView of the widget.

About the RemoteView

    In Part 1, I have not to talk you about RemoteViews and widget layout yet, now I will explain some main features of this property.
    Of course, you must define an initial layout for your widget in XML and save it in the project's res/layout/ directory. In this example, it will be like this:

widget_broadcast.xml

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

    <TextView
        android:id="@+id/txt_widget"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorPrimary"
        android:gravity="center"
        android:text="Click to get current time"
        android:textColor="#ffffff"
        android:textSize="20sp"
        android:textStyle="bold|italic"/>

</LinearLayout>

    Creating the widget layout is simple if you're familiar with Layouts. However, you must be aware that widget layouts are based on RemoteViews, which do not support every kind of layout or view widget.
    A RemoteViews object (and, consequently, a widget) can support the following layout classes:

• FrameLayout
• LinearLayout
• RelativeLayout
• GridLayout

    And the following widget classes: AnalogClock, Button, Chronometer, ImageButton, ImageView, ProgressBar, TextView, ViewFlipper, ListView, GridView, StackView, AdapterViewFlipper.
    Descendants of these classes are not supported. RemoteViews also supports ViewStub, which is an invisible, zero-sized View you can use to lazily inflate layout resources at runtime.

Updating when clicked - programmatically code

    You always have to create a subclass of AppWidgetProvider to managing the widget lifecycle. Please take a look at this class first:

BroadcastWidget.java

package info.devexchanges.broadcastwiget;

import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.widget.RemoteViews;

import java.util.Calendar;

public class BroadcastWidget extends AppWidgetProvider  {
    private static final String ACTION_BROADCASTWIDGETSAMPLE = "ACTION_BROADCASTWIDGETSAMPLE";

    private void updateAppWidget(Context context, AppWidgetManager appWidgetManager,
                                int appWidgetId) {

        // Build the RemoteViews object
        RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.widget_broadcast);

        // Create an Intent which is pointing this class
        Intent intent = new Intent(context, BroadcastWidget.class);
        intent.setAction(ACTION_BROADCASTWIDGETSAMPLE);
        // And this time we are sending a broadcast with getBroadcast
        PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

        // Update widget when clicked
        views.setOnClickPendingIntent(R.id.txt_widget, pendingIntent);
        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);
        }
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        super.onReceive(context, intent);
        if (ACTION_BROADCASTWIDGETSAMPLE.equals(intent.getAction())) {
            RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.widget_broadcast);
            views.setTextViewText(R.id.txt_widget, getCurrentDateTime());

            // This time we don't have widgetId. Reaching our widget with that way
            ComponentName appWidget = new ComponentName(context, BroadcastWidget.class);
            AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);

            // Update the widget
            appWidgetManager.updateAppWidget(appWidget, views);
        }
    }

    private String getCurrentDateTime() {
        Calendar c = Calendar.getInstance();
        int second = c.get(Calendar.SECOND);
        int minute = c.get(Calendar.MINUTE);
        int hour = c.get(Calendar.HOUR_OF_DAY);

        return hour + ":" + minute + ":" + second;
    }
}

    In previous example we used getActivity(), this time we are going to use getBroadcast() when instruct the AppWidgetManager to update the widget.
    To get current time, I use java.util.Calendar, on other way, you can use a Date instance!
    When user clicked at the TextView, onReceive() will be called and in this method, we get current time and shown by this TextView.
    For another step about creating this widget, please read at Part 1.
    NOTE: You can send whatever you want with broadcast and you can catch the broadcast wherever you want.

Running application

    Just keeping the default code of MainActivity, running this app, you'll see "Hello, World" text:

    And the widget is installed, you can find it at WIDGETS tab of the device. Drag it to Home screen to use:

    And when you click on the widget text:

Conclusions

    I've just introduce an another example/feature of Android app widget: updating information when user clicked. Hope this post is helpful with all readers in your own work. Up to Part 3, I will talk about configurable widget with an Activity, coming soon!
   
    Update: Part 3 - Configurable widget now available HERE!

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Author : Hong Thai

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