Question

I want to know if we can call Ondraw() method of Android conditionally based on some flag. For example ondraw() should be called only when a particular frame is decoded.

Consider this situation:

decoder();  /// @NDK 

set flag;   

if (Flag==set)

{

OnDraw() works and displays an image

}       

else

OnDraw sleeps;

Can we implement such type of activities in Android, if yes then how?

Answer 1

In your comment you requested some sample code.
I imagine you have a custom view in your layout which displays the decoded frames. In principle it could look like this:

class FrameView extends View {

    private Bitmap mBitmap;

    public FrameView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        //Your drawing logic
        canvas.drawBitmap(mBitmap,0,0, null);
    }

    private void setFrame(final Bitmap b){
        if (mBitmap!=null){
            mBitmap.recycle();
        }
        mBitmap = b;
        //trigger onDraw, if this method is not called from a ui thread switch to postInvalidate()
        this.invalidate();
    }
}

You grab a handle to this View by calling findViewById() in your activity. Then in your decode thread you call setFrame on the view. Take care to use postInvalidate() if setFrame is called from outside the UI-thread.