Question

I’m trying to have my Activity update an ImageView whenever a boolean value changes in another class.

Therefore i have some sort of timer that starts on my first onCreate()

private void startTimer() {
    mHandler.removeCallbacks(mUpdateTimeTask);
    mHandler.postDelayed(mUpdateTimeTask, 2000); // first run after 2 secs
}

private Runnable mUpdateTimeTask = new Runnable() {
    public void run() {
        connectionControl.checkNetworkState();
        System.out.println("online?: " + connectionControl.isOnline());
        mHandler.postDelayed(this, 15000); // repeat every x/1000 secs
    }
};

My class ConnectionControl has a boolean, that gets set to either true or false whether my app can reach a specific http-host.
Now my question is: how can i achieve a automatic change on the ImageView in my Activity to display the boolean’s value?
I already looked at Observer-Pattern, EventListener, BroadcastReciever but I’m stuck at finding the right solution.
Also, i want to use the listening in other Activities.

What has worked so far was starting/stopping the timer-thing for each activity and have the ImageView update inside the run() method. But my guess is, there has to be a way around the redundancy.

Answer 1

Here is how I did it.

I made a layout file for the custom titlebar thing, that has an ImageView.

<merge xmlns:android="http://schemas.android.com/apk/res/android">
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent" android:layout_height="wrap_content">

    <ImageView android:id="@+id/title_statusimg"
        android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:src="@drawable/connected" android:layout_centerVertical="true"
        android:layout_alignParentRight="true" />

    </RelativeLayout>
</merge> 

I include this in every activities layout file i want to use it.

<include layout="@layout/titlebar" />

Also, i made a StatusActivity that extends Activity. It receives a Broadcast that is send from whenever an background thread detects a change in the connectivity to the webserver.

public class StatusActivity extends Activity {

private String CONNECTION_STATUS = "app.CONNECTION_STATUS";
private ImageView conn;

@Override
protected void onResume() {
    super.onResume();
    IntentFilter iFilter = new IntentFilter(CONNECTION_STATUS);
    registerReceiver(mBroadcastReceiver, iFilter);

    conn = (ImageView) findViewById(R.id.title_statusimg);
    if (ConnectionControl.isOnline()) {
        conn.setImageResource(R.drawable.connected);
    } else {
        conn.setImageResource(R.drawable.nconnected);
    }
}

@Override
protected void onPause() {
    super.onPause();
    unregisterReceiver(mBroadcastReceiver);
}


private BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (ConnectionControl.isOnline()) {
            conn.setImageResource(R.drawable.connected);
        } else {
            conn.setImageResource(R.drawable.nconnected);
        }
    }
};

}

Every Activity that shall use this Status-Image extends StatusActivity instead of Activity.

Hope i covered everything, atleast for me it’s working.