Question

I’ve been a long journey trying to drag and drop UIImageViews from a UITableView to another view.

I have everything working to a point. I subclass UIPanGestureRecognizer and attach this custom recognizer to all the UIImageViews I load into the table view.

I then override the recognizer’s touchesMoved method to, among other things, add a temporary view onto the applications key window, then add a copy of the selected UIImageView onto this temporary view, as follows:

UIView *dragAndDropView = [[UIView alloc] initWithFrame: [[UIScreen mainScreen] applicationFrame]];
        dragAndDropView.backgroundColor = [UIColor whiteColor];

        [[UIApplication sharedApplication].keyWindow addSubview: dragAndDropView]; 

        ElementImageView * sourceImageView = (ElementImageView*)self.view;

        ElementImageView *newImageView =  [[ElementImageView alloc] initWithImage:sourceImageView.image];
        newImageView.userInteractionEnabled = YES;
        newImageView.frame = [self.view convertRect:sourceImageView.frame toView:dragAndDropView];

        [dragAndDropView addSubview:newImageView];

As a result of this code, I do indeed get a copy of the source image view on top of my dragAndDropView (I can tell because I set the backgroundcolor of the dragAndDropView to white). And if I lift my finger and touch the copied image view again, I can of course drag it around the screen as I wish. But I can’t find a way to seamlessly transfer the existing touch to the new object.

Any ideas?

Answer 1

I think you could do the following on your UIPanGestureRecognizer handler:

-(void) handlePan:(UIPanGestureRecognizer *)recognizer  {

if (recognizer.state == UIGestureRecognizerStateBegan) {

    // the initial position
    initialPanPositionX = self.transform.tx;
    initialPanPositionY = self.transform.ty;

    // create a copy of the imageview
    panImage = [[UIImageView alloc] initWithImage:imageView.image];
    panImage.frame = imageView.frame;

    [self.view addSubview:panImage];

}
else if (recognizer.state == UIGestureRecognizerStateChanged) {

    if (!startedMoving) {
        startedMoving = YES;

        [UIView beginAnimations:nil context:NULL]; {
            [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
            [UIView setAnimationDuration:0.2f];

            // an effect to increase a copy a little bit when start dragging
            CGAffineTransform zt = CGAffineTransformScale(CGAffineTransformIdentity, 1.2, 1.2);

            panImage.bounds = CGRectApplyAffineTransform(panImage.bounds, zt);

        }
        [UIView commitAnimations];

    }

    // translation
    CGPoint point = [recognizer translationInView:self];
    panImage.transform = CGAffineTransformMakeTranslation(initialPanPositionX + point.x, initialPanPositionY + point.y);


}
else if (recognizer.state == UIGestureRecognizerStateEnded ) {

    startedMoving = NO;

    // drop the imageView if it's inside the droppable view


    [panImage release], panImage = nil;

}

}

Hope it helps.