Drag and move a circle drawn on canvas

I am working on an Android application which should allow user to draw a circle on canvas and drag it . I have been able to draw lines and circles on it.But I cant seem to be able to drag it.

Is it possible to drag an object drawn on canvas in Android?.For example if I detect a touch within the circle, how do I delete the circle from a previous position and move it to the current position? I have tried invalidate().But it wont work if the user has drawn multiple circle and wants to move all of them.

It seems that you might have issues with handling of multi-touch / drawing. There's some usefull tutorials about it on Android Developer site and on Android Blog.

Based on this I was able to create an example which I think quite similar to that You're trying to achieve (without complete circle drawing - circles get generated by single touch):

public class CirclesDrawingView extends View {

    private static final String TAG = "CirclesDrawingView";

    /** Main bitmap */
    private Bitmap mBitmap = null;

    private Rect mMeasuredRect;

    /** Stores data about single circle */
    private static class CircleArea {
        int radius;
        int centerX;
        int centerY;

        CircleArea(int centerX, int centerY, int radius) {
            this.radius = radius;
            this.centerX = centerX;
            this.centerY = centerY;
        }

        @Override
        public String toString() {
            return "Circle[" + centerX + ", " + centerY + ", " + radius + "]";
        }
    }

    /** Paint to draw circles */
    private Paint mCirclePaint;

    private final Random mRadiusGenerator = new Random();
    // Radius limit in pixels
    private final static int RADIUS_LIMIT = 100;

    private static final int CIRCLES_LIMIT = 3;

    /** All available circles */
    private HashSet<CircleArea> mCircles = new HashSet<CircleArea>(CIRCLES_LIMIT);
    private SparseArray<CircleArea> mCirclePointer = new SparseArray<CircleArea>(CIRCLES_LIMIT);

    /**
     * Default constructor
     *
     * @param ct {@link android.content.Context}
     */
    public CirclesDrawingView(final Context ct) {
        super(ct);

        init(ct);
    }

    public CirclesDrawingView(final Context ct, final AttributeSet attrs) {
        super(ct, attrs);

        init(ct);
    }

    public CirclesDrawingView(final Context ct, final AttributeSet attrs, final int defStyle) {
        super(ct, attrs, defStyle);

        init(ct);
    }

    private void init(final Context ct) {
        // Generate bitmap used for background
        mBitmap = BitmapFactory.decodeResource(ct.getResources(), R.drawable.up_image);

        mCirclePaint = new Paint();

        mCirclePaint.setColor(Color.BLUE);
        mCirclePaint.setStrokeWidth(40);
        mCirclePaint.setStyle(Paint.Style.FILL);
    }

    @Override
    public void onDraw(final Canvas canv) {
        // background bitmap to cover all area
        canv.drawBitmap(mBitmap, null, mMeasuredRect, null);

        for (CircleArea circle : mCircles) {
            canv.drawCircle(circle.centerX, circle.centerY, circle.radius, mCirclePaint);
        }
    }

    @Override
    public boolean onTouchEvent(final MotionEvent event) {
        boolean handled = false;

        CircleArea touchedCircle;
        int xTouch;
        int yTouch;
        int pointerId;
        int actionIndex = event.getActionIndex();

        // get touch event coordinates and make transparent circle from it
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                // it's the first pointer, so clear all existing pointers data
                clearCirclePointer();

                xTouch = (int) event.getX(0);
                yTouch = (int) event.getY(0);

                // check if we've touched inside some circle
                touchedCircle = obtainTouchedCircle(xTouch, yTouch);
                touchedCircle.centerX = xTouch;
                touchedCircle.centerY = yTouch;
                mCirclePointer.put(event.getPointerId(0), touchedCircle);

                invalidate();
                handled = true;
                break;

            case MotionEvent.ACTION_POINTER_DOWN:
                Log.w(TAG, "Pointer down");
                // It secondary pointers, so obtain their ids and check circles
                pointerId = event.getPointerId(actionIndex);

                xTouch = (int) event.getX(actionIndex);
                yTouch = (int) event.getY(actionIndex);

                // check if we've touched inside some circle
                touchedCircle = obtainTouchedCircle(xTouch, yTouch);

                mCirclePointer.put(pointerId, touchedCircle);
                touchedCircle.centerX = xTouch;
                touchedCircle.centerY = yTouch;
                invalidate();
                handled = true;
                break;

            case MotionEvent.ACTION_MOVE:
                final int pointerCount = event.getPointerCount();

                Log.w(TAG, "Move");

                for (actionIndex = 0; actionIndex < pointerCount; actionIndex++) {
                    // Some pointer has moved, search it by pointer id
                    pointerId = event.getPointerId(actionIndex);

                    xTouch = (int) event.getX(actionIndex);
                    yTouch = (int) event.getY(actionIndex);

                    touchedCircle = mCirclePointer.get(pointerId);

                    if (null != touchedCircle) {
                        touchedCircle.centerX = xTouch;
                        touchedCircle.centerY = yTouch;
                    }
                }
                invalidate();
                handled = true;
                break;

            case MotionEvent.ACTION_UP:
                clearCirclePointer();
                invalidate();
                handled = true;
                break;

            case MotionEvent.ACTION_POINTER_UP:
                // not general pointer was up
                pointerId = event.getPointerId(actionIndex);

                mCirclePointer.remove(pointerId);
                invalidate();
                handled = true;
                break;

            case MotionEvent.ACTION_CANCEL:
                handled = true;
                break;

            default:
                // do nothing
                break;
        }

        return super.onTouchEvent(event) || handled;
    }

    /**
     * Clears all CircleArea - pointer id relations
     */
    private void clearCirclePointer() {
        Log.w(TAG, "clearCirclePointer");

        mCirclePointer.clear();
    }

    /**
     * Search and creates new (if needed) circle based on touch area
     *
     * @param xTouch int x of touch
     * @param yTouch int y of touch
     *
     * @return obtained {@link CircleArea}
     */
    private CircleArea obtainTouchedCircle(final int xTouch, final int yTouch) {
        CircleArea touchedCircle = getTouchedCircle(xTouch, yTouch);

        if (null == touchedCircle) {
            touchedCircle = new CircleArea(xTouch, yTouch, mRadiusGenerator.nextInt(RADIUS_LIMIT) + RADIUS_LIMIT);

            if (mCircles.size() == CIRCLES_LIMIT) {
                Log.w(TAG, "Clear all circles, size is " + mCircles.size());
                // remove first circle
                mCircles.clear();
            }

            Log.w(TAG, "Added circle " + touchedCircle);
            mCircles.add(touchedCircle);
        }

        return touchedCircle;
    }

    /**
     * Determines touched circle
     *
     * @param xTouch int x touch coordinate
     * @param yTouch int y touch coordinate
     *
     * @return {@link CircleArea} touched circle or null if no circle has been touched
     */
    private CircleArea getTouchedCircle(final int xTouch, final int yTouch) {
        CircleArea touched = null;

        for (CircleArea circle : mCircles) {
            if ((circle.centerX - xTouch) * (circle.centerX - xTouch) + (circle.centerY - yTouch) * (circle.centerY - yTouch) <= circle.radius * circle.radius) {
                touched = circle;
                break;
            }
        }

        return touched;
    }

    @Override
    protected void onMeasure(final int widthMeasureSpec, final int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        mMeasuredRect = new Rect(0, 0, getMeasuredWidth(), getMeasuredHeight());
    }
}

Activity contains only setContentView(R.layout.main) there main.xml is the following:

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:id="@+id/scroller">
    <com.example.TestApp.CirclesDrawingView
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>