Question

I have a custom view called DrawView created in the main activity. I have implemented the onDraw() method in the DrawView class and it initially draws a circle. I have then added a touch listener, so that when a user clicks, it then draws a square. I am up to the part where the user clicks and a square is drawn. I’m not to sure how to go about this.

public class TestActivity extends Activity {
    DrawView drawing;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ViewGroup myLayout = (ViewGroup) findViewById(R.id.mainLayout);

        drawing = new DrawView(this);
        myLayout.addView(drawing);  

        drawing.setOnTouchListener(new View.OnTouchListener() {

            public boolean onTouch(View v, MotionEvent event) {
                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    // draw a square
                }
                return true;
            }
        });
    }

    private class DrawView extends View {

        public DrawView(Context context) {
            super(context);
        }

        protected void onDraw(Canvas canvas) {
            Paint myPaint = new Paint();
            myPaint.setColor(Color.BLACK);
            // draw a circle
        }
    }
}

Help would be much appreciated.

Answer 1

here is the simple snippet for drawing the rectangle when user down,move and up of touch listener fire, just override in DrawView class not by setOnTouchListener()

define the Rect r = new Rect() in DrawView class then after implement this code in DrawView class

public boolean onTouch(View v, MotionEvent event) {
   if (event.getAction() == MotionEvent.ACTION_DOWN) {
      sx = event.getX();
      sy = event.getY();
      r.set(sx,sy,sx,sy);
   }else if(event.getAction==MotionEvent.ACTION_UP){
      r.set(sx,sy,event.getX(),event.getY());
   }else if(event.getAction==MotionEvent.ACTION_MOVE){
      r.set(sx,sy,event.getX(),event.getY());
   }
   invalidate();
   return true;

}

here is the onDraw()

public void onDraw(Canvas canvas){
    super.onDraw(canvas);
    canvas.drawRect(r, new Paint());
}