Android touchevent--- need help/suggestion according to scenario

Now I have an ImageView and its a circle which is at the slightly below than center position (But this should not matter).

I have written code onTouch of ImageView for ACTION_DOWN,ACTION_UP ,now consider as user have put finger on circle and move and move.... I want to active some code when user move finger and exceed the region of CIRCLE image(As soon as user exceed the region the code should be ececuted onlly once)

Here is my code

ImageView view1 = (ImageView) findViewById(R.id.fccircledetectionarea);

      view1.setOnTouchListener(new OnTouchListener()
      {

        @Override
        public boolean onTouch(View v, MotionEvent event) 
        {
            ImageView imageView=(ImageView) findViewById(R.id.fccircledetectionarea);
            switch(event.getAction())
            {
            case MotionEvent.ACTION_DOWN:
           开发者_运维知识库     final float x=imageView.getTop();


                Toast.makeText(PlayScreen.this, "Top Position:"+x, Toast.LENGTH_SHORT).show();
                break;
            case MotionEvent.ACTION_UP:
                Toast.makeText(PlayScreen.this, "Over", Toast.LENGTH_SHORT).show();
                break;

            case MotionEvent.ACTION_MOVE:


                Toast.makeText(PlayScreen.this, "Over", Toast.LENGTH_SHORT).show();
                break;

            }
            return true;
        }
    });

I cannot archive my goal through ACTION_MOVE: as it start to work if user move finger within the circle

And my second query is that How to set alpha of this imageview I have used

view1.setAlpha(0);

But is not working and I have also made this imageview invisible but than my onTouch code is not working

Within your onTouch method record a boolean to check if the user is touching within the bounds of the circle.

boolean inCircle = java.lang.Math.sqrt(x*x + y*y) <= circleRadius

Where x is taken from event.getX() - circleCenterX and y is taken from event.getY() - circleCenterY (touch position's offset from center of the circle)