Question

I have the following code in my app which I could just copy and paste each time, but I would rather make it so it is reusable in other areas too. It allows me to drag UIImageViews around the screen but I don’t like the fact that it is very prone to error with the slightest of typos!

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint location = [touch locationInView:self.view];




if (touch.view == first) {
    first.center = location;

    if (((first.center.x >= 100) && (first.center.y >= 100) &&
         (first.center.x <= 150) && (first.center.y <= 150))) {

        first.center = CGPointMake(125, 125);
        [first setUserInteractionEnabled:NO];

        theCentre = [[NSUserDefaults standardUserDefaults] init];

        NSString *centre = NSStringFromCGPoint(first.center);

        [theCentre setObject:centre forKey:@"centre"];

        //  NSLog(@"%@", [theCentre objectForKey:@"centre"]);
        [theCentre synchronize];

    }

}
if (touch.view == second) {
    second.center = location;

    if (((second.center.x >= 150) && (second.center.y >= 150) &&
         (second.center.x <= 180) && (second.center.y <= 180))) {

        second.center = CGPointMake(165, 165);
        [second setUserInteractionEnabled:NO];

        theCentre = [[NSUserDefaults standardUserDefaults] init];

        NSString *centre = NSStringFromCGPoint(second.center);

        [theCentre setObject:centre forKey:@"secondCentre"];

        //  NSLog(@"%@", [theCentre objectForKey:@"centre"]);
        [theCentre synchronize];
}
}
if (touch.view == third) {
    third.center = location;

    if (((third.center.x >= 200) && (third.center.y >= 200) &&
         (third.center.x <= 230) && (third.center.y <= 230))) {

        third.center = CGPointMake(215, 215);
        [third setUserInteractionEnabled:NO];

        theCentre = [[NSUserDefaults standardUserDefaults] init];

        NSString *centre = NSStringFromCGPoint(third.center);

        [theCentre setObject:centre forKey:@"thirdCentre"];

        //  NSLog(@"%@", [theCentre objectForKey:@"centre"]);
        [theCentre synchronize];
    }

}  

}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
[self touchesBegan:touches withEvent:event];
}

I have tried fast enumeration but that made one imageView move and the others just disappear off the screen! Obviously not the desired effect…

Answer 1

I recommend using UIGestureRecognizers for this. After you set up your image views write:

NSArray *imageViews = [NSArray arrayWithObjects:first, second, third, nil];
for (UIView *imageView in imageViews) {
    UIPanGestureRecognizer *panGR = [[UIPanGestureRecognizer alloc] 
        initWithTarget:self action:@selector(handlePanGesture:)]
    [imageView addGestureRecognizer:panGR];
    [panGR release];
}

And then implement the gesture handler:

- (void)handlePanGesture:(UIGestureRecognizer *)gestureRecognizer {
    UIPanGestureRecognizer *panGR = (UIPanGestureRecognizer *)gestureRecognizer;
    UIView *gestureView = [panGR view];
    CGPoint translation = [panGR translationInView:gestureView];
    gestureView.center = CGPointMake(gestureView.center.x + translation.x,
                                     gestureView.center.y + translation.y);
    [panGR setTranslation:CGPointZero inView:gestureView];
}

This code is untested (written in notepad), but this is the right direction.