Creating a draggable image view - objective-c

Question

I have been searching the net for a long time and I have not found a concrete way of making an image view draggable. Here is what I have so far:
tempViewController.h
#import <UIKit/UIKit.h>
#import "MyRect.h"
#class UIView;
#interface tempViewController : UIViewController
#property (nonatomic, strong) MyRect *rect1;
#end
tempViewController.m
#import "tempViewController.h"
#interface tempViewController ()
#end
#implementation tempViewController
#synthesize rect1 = _rect1;
- (void)viewDidLoad
{
[super viewDidLoad];
_rect1 = [[MyRect alloc]initWithFrame:CGRectMake(150.0, 100.0, 80, 80)];
[_rect1 setImage:[UIImage imageNamed:#"cloud1.png"]];
[_rect1 setUserInteractionEnabled:YES];
[self.view addSubview:_rect1];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [[event allTouches]anyObject];
if([touch view] == _rect1)
{
CGPoint pt = [[touches anyObject] locationInView:_rect1];
NSLog(#"%#",NSStringFromCGPoint(pt));
_rect1.center = pt;
}
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [[event allTouches]anyObject];
if([touch view] == _rect1)
{
CGPoint pt = [[touches anyObject] locationInView:_rect1];
NSLog(#"%#",NSStringFromCGPoint(pt));
_rect1.center = pt;
}
}
#end
MyRect right now is an empty UIImageView Class.
Dragging the image from a point such as [532,589] on micron moves it to a totally different part of the screen such as [144, 139]

Answer 1

Just attach a UIPanGestureRecognizer to your view. In the recognizer's action, update your view's center based on the “translation” (offset) of the recognizer, then reset the recognizer's translation to zero. Here's an example:
- (void)viewDidLoad {
[super viewDidLoad];
UIView *draggableView = [[UIView alloc] initWithFrame:CGRectMake(150, 100, 80, 80)];
draggableView.userInteractionEnabled = YES;
draggableView.backgroundColor = [UIColor redColor];
[self.view addSubview:draggableView];
UIPanGestureRecognizer *panner = [[UIPanGestureRecognizer alloc]
initWithTarget:self action:#selector(panWasRecognized:)];
[draggableView addGestureRecognizer:panner];
}
- (void)panWasRecognized:(UIPanGestureRecognizer *)panner {
UIView *draggedView = panner.view;
CGPoint offset = [panner translationInView:draggedView.superview];
CGPoint center = draggedView.center;
draggedView.center = CGPointMake(center.x + offset.x, center.y + offset.y);
// Reset translation to zero so on the next `panWasRecognized:` message, the
// translation will just be the additional movement of the touch since now.
[panner setTranslation:CGPointZero inView:draggedView.superview];
}

Answer 2

Don't use -touchesBegan:withEvent: etc.
What you want to use for such "high-level" things are UIGestureRecognizers.
You would add a pan gesture recognizer to your view set a delegate (possibly the view itself), and in the callback move the view by the distance the recognizer moved.
You either remember the initial position and move by the -translationInView each time, or simply move by the translation and then use -setTranslation:inView: to reset the recognizers translation to zero, so on the next call of the delegate method, you will again get the movement since the last call.