Android: Need to use onSizeChanged for View.getWidth/Height() in class extending Activity

Question

I want to use getWidth()/getHeight() to get width/height of my XML-Layout. I read I have to do it in the method onSizeChanged() otherwise I will get 0 ( Android: Get the screen resolution / pixels as integer values ).

But I want to do it in a class already extending Activity. So I think it's not possible let the same class extending View.

public class MyClass extends Activity {

    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
        ViewGroup xml_layout = (ViewGroup) findViewById(R.id.layout_id);  
        TextView tv = new TextView(this);  
        tv = (TextView) findViewById(R.id.text_view);  
        int layout_height = xml_layout.getHeight();  
        int layout_width = xml_layout.getWidth();
    }  

    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        //Error, because I need to use extends View for class, but I can't do it because I also need extends Activity to use onCreate
    }
}

If I use MyClass extends Activity I can use onCreate but not onSizeChanged.
If I use MyClass extends View I can use onSizeChangedbut not onCreate.

How can I solve the problem?

Answer 1

You dont have to create a customView to get its height and width. You can add an OnLayoutChangedListener (description here) to the view whose width/height you want, and then essentially get the values in the onLayoutChanged method, like so

View myView = findViewById(R.id.my_view);
myView.addOnLayoutChangeListener(new OnLayoutChangeListener() {

        @Override
        public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight,
                int oldBottom) {
            // its possible that the layout is not complete in which case
            // we will get all zero values for the positions, so ignore the event
            if (left == 0 && top == 0 && right == 0 && bottom == 0) {
                return;
            }

           // Do what you need to do with the height/width since they are now set
        }
    });

The reason for this is because views are drawn only after the layout is complete. The system then walks down the view heirarchy tree to measure the width/height of each view before drawing them.