How to set ontouch listener for something drawn using canvas: Android

Question

I have a custom view in which i am drawing one big circle and a small circle on the edge of this big circle.

I would like to move the small circle and so would like

Answer 1

try this (this is a little modified version of MyView i already posted as an answer for your previous question):

public class MyView extends View {
    private final static String TAG = "Main.MyView";

    private static final float CX = 0;
    private static final float CY = 0;
    private static final float RADIUS = 20;
    private static final float BIGRADIUS = 50;
    private static final int NORMAL_COLOR = 0xffffffff;
    private static final int PRESSED_COLOR = 0xffff0000;

    private Paint mPaint;
    private Path mSmallCircle;
    private Path mCircle;
    private Matrix mMatrix;
    private float mAngle;

    private int mSmallCircleColor;

    public MyView(Context context) {
        super(context);
        mPaint = new Paint();

        mSmallCircle = new Path();
        mSmallCircle.addCircle(BIGRADIUS + RADIUS + CX, CY, RADIUS, Direction.CW);
        mSmallCircleColor = NORMAL_COLOR;

        mCircle = new Path();
        mCircle.addCircle(0, 0, BIGRADIUS, Direction.CW);

        mMatrix = new Matrix();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        if (action == MotionEvent.ACTION_UP) {
            mSmallCircleColor = NORMAL_COLOR;
            invalidate();
            return false;
        }
        float w2 = getWidth() / 2f;
        float h2 = getHeight() / 2f;
        float r = 0;
        if (action == MotionEvent.ACTION_DOWN) {
            float[] pts = {
                    BIGRADIUS + RADIUS + CX, CY
            };
            mMatrix.mapPoints(pts);
            r = (float) Math.hypot(event.getX() - pts[0], event.getY() - pts[1]);
        }
        if (r < RADIUS) {
            mSmallCircleColor = PRESSED_COLOR;
            mAngle = (float) (180 * Math.atan2(event.getY() - h2, event.getX() - w2) / Math.PI);
            invalidate();
            return true;
        }
        return false;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        float w2 = getWidth() / 2f;
        float h2 = getHeight() / 2f;
        mMatrix.reset();
        mMatrix.postRotate(mAngle);
        mMatrix.postTranslate(w2, h2);

        canvas.concat(mMatrix);
        mPaint.setColor(0x88ffffff);
        canvas.drawPath(mCircle, mPaint);
        mPaint.setColor(mSmallCircleColor);
        canvas.drawPath(mSmallCircle, mPaint);
    }
}

Answer 2

You can get the rectangle of your touch point and the rectangle(position) of your inner circle and check if they cross over with the Intersects method.

http://docs.oracle.com/javase/7/docs/api/java/awt/Rectangle.html#intersects(java.awt.Rectangle)

Your canvas onTouchListener can do whatever it needs to do if the touchpoint intersect your circle.

e.g:

    // Create a rectangle from the point of touch
    Rect touchpoint = new Rect(x,y,10,10);

    // Create a rectangle from the postion of the circle.
    Rect myCircle=new Rect(10,10,20,20);

    if (Rect.intersects(myCircle,touchpoint)){
        Log.d("The circle was touched");
    }