Custom Widget using LinearLayout not getting onDraw()

Question

I'm creating a custom widget by extending LinearLayout:

public class MyWidget extends LinearLayout {     private static Paint PAINT = new Paint(Paint.ANTI_ALIAS_FLAG);     static {         PAINT.setColor(Color.RED);     }      public MyWidget(Context context) {         this(context, null);     }      public MyWidget(Context context, AttributeSet attrs) {         super(context, attrs);     }      @Override     protected void onDraw(Canvas canvas) {         super.onDraw(canvas);         canvas.drawCircle(canvas.getWidth() / 2, canvas.getHeight()/2, canvas.getWidth()/2, PAINT);         // never gets called :-(     }      @Override     protected void dispatchDraw(Canvas canvas) {         super.dispatchDraw(canvas);         // this gets called, but with a canvas sized after the padding.     } } 

I can add children just fine, but I'm never getting my custom onDraw() being called. dispatchDraw() gets called, but that seems to have a different canvas (the one that's within the padding. I need to draw on the whole layout area). Is there some flag that needs to get set to get onDraw() called for the layout?

Answer 1

You need to call setWillNotDraw(false) in your constructor.

Because by default a layout does not need to draw, so an optimization is to not call is draw method. By calling setWillNotDraw(false) you tell the UI toolkit that you want to draw.