Question

I have around 16 UIImage views, can be moved by touch. I can drop over UIImage over another UIImage and then the UIImages would exchange their position. Being newcomer to ObjectiveC programming, I am struggling to figure out the UIImageViews and exchange their positons. Till now I am trying to implement in touchesEnded method

    -(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [touches anyObject];
[self.superview exchangeSubviewAtIndex:[[self.superview subviews] indexOfObject:self] withSubviewAtIndex:[[self.superview subviews] indexOfObject:[touch view]]];
}

But this does not work. Any help would be appreciated.

UIImages are created by following code
TouchImageView *touchImageView = [[TouchImageView alloc]initWithImage:displayImage];
        touchImageView.identy = [NSString stringWithFormat:@"Image ID %d",i]; 

So each touch image is associated some string to describe itself.

In touch end, I have just added following code to know ID of image views

UITouch *touch = [touches anyObject];
    TouchImageView *dragImage = (TouchImageView*)[touch view];
    NSLog(@"Ended  %a%a",[dragImage identy],[self identy]);

But the o/p I got is totally different

2011-11-21 11:50:34.404 OrganizeMe[882:f803] Ended  0x1.6d96006a6d96p-9170x1.807p-1022

FInal code

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{

    __block int tag = -1;
    __block float distance = 100000.0;

    [[self.superview subviews] enumerateObjectsUsingBlock:^(UIView *view, NSUInteger index, BOOL *stop) {
        BOOL interSect = CGRectIntersectsRect([self frame], [view frame]);

        if(interSect && ([self tag]!=[view tag])){
            [self.image CGImage];
            CGPoint currPoint = [[touches anyObject]locationInView:[self superview]];
            CGPoint underPoint = view.center;

            if(distance >= [self distanceBetweenPoint1:currPoint Point2:underPoint]){
                distance =  [self distanceBetweenPoint1:currPoint Point2:underPoint] ;
                tag = [view tag];
            }

        }
    }];
    NSLog(@"Tag and Distance %d,%f",tag,distance);
    TouchImageView* imageView1 = (TouchImageView*)[self.superview viewWithTag:tag];
    CGRect point1 = [imageView1 frame];
    CGRect point2 = [self frame];

    if(tag != -1){
        [imageView1 setFrame:point2];
        [self setFrame:point1];
    }else{
        CGPoint lastTouch = [[touches anyObject]previousLocationInView:[self superview]];
        self.center = lastTouch;
    }
    [self.superview setNeedsLayout];

}

Answer 1

The index is just the UIView’s position in the subview array. It does not set the location within the superview.

Relayout the superview based on the subview’s index.

In your above method, also call setNeedsLayout in order to relayout the superview.

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    [self.superview exchangeSubviewAtIndex:[[self.superview subviews] indexOfObject:self] withSubviewAtIndex:[[self.superview subviews] indexOfObject:[touch view]]];
    [self.superview setNeedsLayout]; // Should call the method below
}

Implement the following method for the superview:

- (void)layoutSubviews
{
    // Iterate over all subviews
    [self.subviews enumerateObjectsUsingBlock:^(UIView *view, NSUInteger index, BOOL *stop) {
        // This block will be executed for each subview. You have the subview's index.
        // Now set the subview's position accordingly to the index.
        // I don't know your layout logic, but let's assume you have 14 subviews spread over 4 columns, this will be the subviews' position:
        /*  0  1  2  3
            4  5  6  7
            8  9 10 11
           12 13         */
        int col = index % 4; // Column from 0 to 3
        int row = (int)(index / 4); // Row starting from 0
        int w = view.frame.size.width;
        int h = view.frame.size.height;
        CGPoint p = CGPointMake(col * w + w / 2, row * h + h / 2);
        [view setCenter:p];
    }];
}

It’s been a long time I last used Cocoa touch, so I can’t guarantee that the code is working.