Question

I have a few UIView subclasses that exist in a kind of inventory. When you tap one, another draggable version is placed over top of it. I want the inventory versions to stay put while you drag others around. The code to make a duplicate works but dragging your finger around doesn’t move it.

If I release and then start dragging the newly created version it moves as expected. I think this is because the original touches (that made the dupe) didn’t have the draggable version in the responder chain.

A little code…

in my stationary “icon”…

- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
    [self.viewController placeDraggableItem:self.item WithPoint:self.frame.origin];
}

in my viewController…

- (void)placeDraggableItem:(Item *)item WithPoint:(CGPoint)point
{
    DraggableItem *draggableItem = [[DraggableItem alloc] initWithImage:[UIImage imageNamed:item.graphic]];
draggableItem.frame = CGRectMake(point.x, scrollView.frame.origin.y + point.y, 64.0f, 64.0f);
    [self.view addSubview:draggableItem];   
    [draggableItem release];
}

in my DraggableItem…

- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
    currentPoint = [[touches anyObject] locationInView:self];
}

- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
    CGPoint activePoint = [[touches anyObject] locationInView:self];
    CGPoint newPoint = CGPointMake(self.center.x + (activePoint.x - currentPoint.x), self.center.y + (activePoint.y - currentPoint.y));

    float midPointX = CGRectGetMidX(self.bounds);
    if (newPoint.x > self.superview.bounds.size.width  - midPointX)
        newPoint.x = self.superview.bounds.size.width - midPointX;
    else if (newPoint.x < midPointX)  // If too far left...
        newPoint.x = midPointX;

    float midPointY = CGRectGetMidY(self.bounds);
    if (newPoint.y > self.superview.bounds.size.height  - midPointY)
        newPoint.y = self.superview.bounds.size.height - midPointY;
    else if (newPoint.y < midPointY)  // If too far up...
        newPoint.y = midPointY;

    self.center = newPoint;
}

Now again creating the draggable version works. And the draggable version is able to be moved after you first release your first touch. But I think I need to get the newly create UIView to respond to touches that were originally made for the “icon”.

Any ideas?

I’m aware this question is kind of similar to this one: How to "transfer" first responder from one UIView to another? but in that case the view which should receive the touches is already there whereas I need to pass touches onto a newly created view.

Answer 1

I don’t know of any way to hand touches off to a newly created view, though that doesn’t mean there isn’t a way to do it. It looks like you really only want your draggable view to handle the touches, I would probably create each draggable view with with an alpha of 0 at the same time you create the non draggable views, and in touchesBegan set it to 1. If your non-draggable views don’t need to handle touches, then it doesn’t make sense to make them handle touches just to pass them along.