仅在wifi状态更改时如何更新小部件？

Question

Following this tutorial I quickly created a simple widget which displays and updates the current time every second on the home screen:

Question: I was wondering how this code has to be changed, so that the time is only updated when a certain event occurs. Eg: update the time only if wifi state changes .

Here are the (hopefully) relevant code sections:

<!--  Broadcast Receiver -->
<receiver android:name=".WifiSSIDWidget" android:label="@string/app_name">
    <intent-filter> <action android:name="android.appwidget.action.APPWIDGET_UPDATE"/> 
    </intent-filter>
    <meta-data android:name="android.appwidget.provider" android:resource="@xml/wifi_ssid_widget_provider" />
</receiver>    

Here's the widget class code:

public class HelloWidget extends AppWidgetProvider {

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {

        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new MyTime(context, appWidgetManager), 1, 1000);
    }

    private class MyTime extends TimerTask {
        RemoteViews remoteViews;
        AppWidgetManager appWidgetManager;
        ComponentName thisWidget;
        DateFormat format = SimpleDateFormat.getTimeInstance(SimpleDateFormat.MEDIUM, Locale.getDefault());

    public MyTime(Context context, AppWidgetManager appWidgetManager) {
        this.appWidgetManager = appWidgetManager;
        remoteViews = new RemoteViews(context.getPackageName(), R.layout.main);
        thisWidget = new ComponentName(context, HelloWidget.class);
    }

    @Override
    public void run() {
        remoteViews.setTextViewText(R.id.widget_textview, "TIME = " +format.format(new Date()));
        appWidgetManager.updateAppWidget(thisWidget, remoteViews);
    }

    } 
}

Answer 1

To trigger when a certain event occurs, you create a broastcast receiver in manifest file (note that not all event will be trigger, for example : SMS received can, but SMS sending cannot).

Here is the example for Network State Change.

1) Create a broastcast receiver:

public class NetworkStateChangeReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        Log.i(TAG, "Receive Network State Change");

            // you put your main code here. 
            // or if you don't want, put your code to service. So, run following code
        Intent myIntent = new Intent(context, NetworkStateChangeService .class);
        // put all intent data to this intent
                myIntent.putExtras(intent);
                WakefulIntentService.sendWakefulWork(context, myIntent);

    }
}

2) This broastcast receiver will run code from NetworkStateChangeService . Here is the main code of NetworkStateChangeService :

public class NetworkStateChangeService extends WakefulIntentService {

    public static String TAG = "SMS Service";

    public NetworkStateChangeService() {
        super("Network state change");
    }

    public SMSReceivedService(String name) {
        super(name);
    } 

    @Override
    protected void doWakefulWork(Intent intent) {
            // put your main code here
        }
}

Note : WakefulIntentService is a custom class invented by commonsguy

3) You register your receiver and service in manifest file:

    <receiver android:name="NetworkStateChangeReceiver "> 
                <intent-filter>
                    <action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
                </intent-filter>
      </receiver>

 <service 
            android:name="NetworkStateChangeService">
 </service>

Above is the framework often if you want to do with Broastcast Receiver . As you see some other easier tutorial, they just put main code in onreceive of broadcast receiver , but if your work takes long time, you should put in service, and should use WakefulIntentService because it helps devices awake while doing your work.