Kresleni na dotek obrazovky
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Trida Point
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public class Point {
    float x, y;
    @Override
    public String toString() {
        return x + ", " + y;
    }
}


Trida DrawView
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public class DrawView extends View implements View.OnTouchListener {
    List<Point> points = new ArrayList<Point>();
    Paint paint = new Paint();

    public DrawView(Context context) {
        super(context);
        setFocusable(true);
        setFocusableInTouchMode(true);
        this.setOnTouchListener(this);
        paint.setColor(Color.RED);
        paint.setAntiAlias(true);
    }

    @Override
    public void onDraw(Canvas canvas) {
        for(Point point: points) {
            canvas.drawCircle(point.x, point.y, 5, paint);
        }
    }

    public boolean onTouch(View view, MotionEvent event) {
// if(event.getAction() != MotionEvent.ACTION_DOWN)
// returnsuper.onTouchEvent(event);
        Point point= new Point();
        point.x = event.getX();
        point.y = event.getY();
        points.add(point);
        invalidate();
        return true;
    }

}


MainActivity
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DrawView drawView;

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        drawView = new DrawView(this);
        setContentView(drawView);
        drawView.requestFocus();
    }