ImageView visibility Error with Timer

Question

package name.cpr;

import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import java.util.Timer;
import java.util.TimerTask;

public class ExampleActivity extends ActionBarActivity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_example);
        Timer timer = new Timer();
        timer.schedule(new CheckConnection(), 0, 3000);
        ImageView iv = (ImageView) findViewById(R.id.imageView);
        iv.setVisibility(View.VISIBLE);
    }
    class CheckConnection extends TimerTask{
        public void run(){
            ImageView iv = (ImageView) findViewById(R.id.imageView);
            iv.setVisibility(View.INVISIBLE); //<- Unfortunatly Error Here
        }
    }
}

starting app, first time image view visibility work but with timer not working, if timer started same error Unfortunately .... has stopped

You might want to edit your question mate.Add the error log and add the Android tag :) — cgew85, Dec 16 '14 at 11:44

score 0 · Accepted Answer · answered Dec 16 '14 at 13:40

You may want to use android.os.Handler instead.

public class ExampleActivity extends ActionBarActivity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_example);
        ImageView iv = (ImageView) findViewById(R.id.imageView);
        iv.setVisibility(View.VISIBLE);
        //
        new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {
                        iv.setVisibility(View.INVISIBLE);
                }
        }, 3000);
    }
}

Good Luck. :)

This is the correct approach: using a `Handler`. This code will wait 3 seconds, and then hide the image; the op's code hides the image instantly, than waits 3 secs and hides it again.. and again. — rekaszeru, Dec 16 '14 at 13:45

score 0 · Answer 2 · answered Dec 16 '14 at 13:40

What you are doing is updating a gui element from a non-gui thread, which ends up in a RuntimeException. One way to fix it is to use a Handler:

public class ExampleActivity extends Activity
{
    private ImageView iv;
    private ImgHandler handler;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_example);

        this.iv = (ImageView) findViewById(R.id.imageView);
        this.iv.setVisibility(View.VISIBLE);
        this.handler = new ImgHandler(this.iv);

        final Timer timer = new Timer();
        timer.schedule(new CheckConnection(), 0, 3000);
    }

    /**
     * The timer task to run every 3 seconds
     */
    private final class CheckConnection extends TimerTask
    {
        public void run()
        {
            handler.sendEmptyMessage(0);
        }
    }

    /**
     * Custom <b>static</b> handler to bridge between the timer task's thread and the gui
     */
    private static final class ImgHandler extends Handler
    {
        // use a weak reference to the ImageView instance you'd like to manipulate:
        private final WeakReference<ImageView> imageReference;

        public ImgHandler(final ImageView img)
        {
            this.imageReference = new WeakReference<ImageView>(img);
        }

        @Override
        public void handleMessage(Message msg)
        {
            if (imageReference == null)
                return; // no image to show / hide
            final ImageView img = imageReference.get();
            // since this is the single message we are handling, no switch is used:
            if (img != null)
            {
                img.setVisibility(img.getVisibility() == View.VISIBLE ? View.INVISIBLE : View.VISIBLE);
            }
        }
    }
}

The example above will change the visibility of your imageView every 3 seconds, though it's not clear from your example whether that was your intent.

ImageView visibility Error with Timer

2 Answers2