UIImageView是iOS上最基本的圖片顯示控制元件，但預設情況下是不支援拖動，放大縮小等功能的。後來在stackoverflow上查詢到一種很簡單的方法，加上本人自己的理解，步驟整理如下：

1.開啟userInteractionEnabled

• New image view objects are configured to disregard user events by default. If you want to handle events in a custom subclass of UIImageView, you must explicitly change the value of the property to YES

   after initializing the object.

[imageView setUserInteractionEnabled:YES];

@interface MyViewController : UIViewController <UIGestureRecognizerDelegate>

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
{
    return YES;
}
 

4.定義手勢引發的操作方法。UIImageView物件主要應用三種手勢操作：UIPinchGestureRecognizer，UIPanGestureRecognizer和UIRotationGestureRecognizer，分別對應（二指）放大縮小，拖動和（二指）旋轉的手勢操作。三個對應方法如下：

- (void)pinchGestureDetected:(UIPinchGestureRecognizer *)recognizer
{
    UIGestureRecognizerState state = [recognizer state];
    
    if (state == UIGestureRecognizerStateBegan || state == UIGestureRecognizerStateChanged)
    {
        CGFloat scale = [recognizer scale];
        [recognizer.view setTransform:CGAffineTransformScale(recognizer.view.transform, scale, scale)];
        [recognizer setScale:1.0];
    }
}

- (void)panGestureDetected:(UIPanGestureRecognizer *)recognizer
{
    UIGestureRecognizerState state = [recognizer state];
    
    if (state == UIGestureRecognizerStateBegan || state == UIGestureRecognizerStateChanged)
    {
        CGPoint translation = [recognizer translationInView:recognizer.view];
        [recognizer.view setTransform:CGAffineTransformTranslate(recognizer.view.transform, translation.x, translation.y)];
        [recognizer setTranslation:CGPointZero inView:recognizer.view];
    }
}

- (void)rotationGestureDetected:(UIRotationGestureRecognizer *)recognizer
{
    UIGestureRecognizerState state = [recognizer state];
    
    if (state == UIGestureRecognizerStateBegan || state == UIGestureRecognizerStateChanged)
    {
        CGFloat rotation = [recognizer rotation];
        [recognizer.view setTransform:CGAffineTransformRotate(recognizer.view.transform, rotation)];
        [recognizer setRotation:0];
    }
}

 

    UIPinchGestureRecognizer *pinchGestureRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchGestureDetected:)];
    [pinchGestureRecognizer setDelegate:self];
    [imageView addGestureRecognizer:pinchGestureRecognizer];

    UIRotationGestureRecognizer *rotationGestureRecognizer = [[UIRotationGestureRecognizer alloc] initWithTarget:self action:@selector(rotationGestureDetected:)];
    [rotationGestureRecognizer setDelegate:self];
    [imageView addGestureRecognizer:rotationGestureRecognizer];

    UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGestureDetected:)];
    [panGestureRecognizer setDelegate:self];
    [imageView addGestureRecognizer:panGestureRecognizer];

MyViewController.h

@interface MyViewController : UIViewController <UIGestureRecognizerDelegate>

@property (weak, nonatomic) IBOutlet UIImageView *imageView;
...

@end

@implementation MyViewController

- (void)viewDidLoad {
    [super viewDidLoad];
        
    [self enableGestureOnView:self.imageView];
     
}

#pragma mark - View Gesture Process

- (void)enableGestureOnView:(UIView *)view{
    [view setUserInteractionEnabled:YES];
    // create and configure the pinch gesture
    UIPinchGestureRecognizer *pinchGestureRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchGestureDetected:)];
    [pinchGestureRecognizer setDelegate:self];
    [view addGestureRecognizer:pinchGestureRecognizer];
    
    // create and configure the rotation gesture
    UIRotationGestureRecognizer *rotationGestureRecognizer = [[UIRotationGestureRecognizer alloc] initWithTarget:self action:@selector(rotationGestureDetected:)];
    [rotationGestureRecognizer setDelegate:self];
    [view addGestureRecognizer:rotationGestureRecognizer];
    
    // creat and configure the pan gesture
    UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGestureDetected:)];
    [panGestureRecognizer setDelegate:self];
    [view addGestureRecognizer:panGestureRecognizer];

}

- (void)pinchGestureDetected:(UIPinchGestureRecognizer *)recognizer
{
    UIGestureRecognizerState state = [recognizer state];
    
    if (state == UIGestureRecognizerStateBegan || state == UIGestureRecognizerStateChanged)
    {
        CGFloat scale = [recognizer scale];
        [recognizer.view setTransform:CGAffineTransformScale(recognizer.view.transform, scale, scale)];
        [recognizer setScale:1.0];
    }
}

- (void)rotationGestureDetected:(UIRotationGestureRecognizer *)recognizer
{
    UIGestureRecognizerState state = [recognizer state];
    
    if (state == UIGestureRecognizerStateBegan || state == UIGestureRecognizerStateChanged)
    {
        CGFloat rotation = [recognizer rotation];
        [recognizer.view setTransform:CGAffineTransformRotate(recognizer.view.transform, rotation)];
        [recognizer setRotation:0];
    }
}

- (void)panGestureDetected:(UIPanGestureRecognizer *)recognizer
{
    UIGestureRecognizerState state = [recognizer state];
    
    if (state == UIGestureRecognizerStateBegan || state == UIGestureRecognizerStateChanged)
    {
        CGPoint translation = [recognizer translationInView:recognizer.view];
        [recognizer.view setTransform:CGAffineTransformTranslate(recognizer.view.transform, translation.x, translation.y)];
        [recognizer setTranslation:CGPointZero inView:recognizer.view];
    }
}

-(BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{
    return YES;
}

參考資料：

1. http://stackoverflow.com/questions/3907397/uigesturerecognizer-on-uiimageview/18622373#18622373
2. https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIImageView_Class/index.html