Question

I am playing with UI Event Handling, and I have found something that I cannot find the explanation from the Android Dev: I have an ImageView, and a TextView , whenever I touch on the ImageView, the TextView show a message. But the following codes doesn’t work:

    public class ShowSomething extends Activity {
 private LinearLayout ll;

 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);

  setContentView(R.layout.main);  

  LinearLayout ll = (LinearLayout)findViewById(R.id.linearLayout);
  final TextView textview = (TextView)findViewById(R.id.textview);
  MyImageView image = new MyImageView(this, textview);
  image.setImageResource(R.drawable.icon);
  ll.addView(image, 48, 48);

 }
}

And MyImageView.java

public class MyImageView extends ImageView implements OnTouchListener{


 private TextView textview;

 public MyImageView(Context context,TextView textview) {
  super(context);
  this.textview = textview;
 }

 @Override
 public boolean onTouch(View v, MotionEvent event) {
  textview.setText("Event captured !");
  return true;
 }
}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/linearLayout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
>
<TextView
android:id="@+id/textview"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Holder"
/>
</LinearLayout>

But when I attach an OnTouchListener on the MyImageView like this, it does work:
File ShowSomething.java

public class ShowSomething extends Activity {

 private LinearLayout ll;

 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);

  setContentView(R.layout.main);  

  LinearLayout ll = (LinearLayout)findViewById(R.id.linearLayout);
  final TextView textview = (TextView)findViewById(R.id.textview);


  MyImageView image = new MyImageView(this,textview);
  image.setImageResource(R.drawable.icon);
  image.setOnTouchListener(new OnTouchListener() {  
     @Override
     public boolean onTouch(View v, MotionEvent event) {
      textview.setText("Event captured!");      
      return false;
     }
    });
  ll.addView(image, 48, 48);

 } 

}

And file MyImageView.java

public class MyImageView extends ImageView { 


 private TextView textview;

 public MyImageView(Context context,TextView textview) {
  super(context);
  this.textview = textview;
 }


}

But as far as I know, the 2 implementation is the same (implement an Event Listener) – do I misunderstand anything ?

Answer 1

For the first case, the right way would be:

MyImageView image = new MyImageView(this, textview);
image.setImageResource(R.drawable.icon);
image.setOnTouchListener(image);

or call setOnTouchListener(this) inside your MyImageView class.