UIView的视图拖动实现可以通过Touch的触摸事件来实现，也可以在UIView中添加拖动手势来实现.

拖动动画.gif

UITouch

UIView是UIResponder的子类，触摸的时候只需要重写对应的触摸方法即可.

// Generally, all responders which do custom touch handling should override all four of these methods.
// Your responder will receive either touchesEnded:withEvent: or touchesCancelled:withEvent: for each
// touch it is handling (those touches it received in touchesBegan:withEvent:).
// *** You must handle cancelled touches to ensure correct behavior in your application.  Failure to
// do so is very likely to lead to incorrect behavior or crashes.
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEstimatedPropertiesUpdated:(NSSet<UITouch *> *)touches NS_AVAILABLE_IOS(9_1);

@implementation TouchView

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"FlyElephant---触摸开始");
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    
    UITouch *touch = [touches anyObject];

    CGPoint currentPoint = [touch locationInView:self];
    // 获取上一个点
    CGPoint prePoint = [touch previousLocationInView:self];
    CGFloat offsetX = currentPoint.x - prePoint.x;
    CGFloat offsetY = currentPoint.y - prePoint.y;
    
    NSLog(@"FlyElephant----当前位置:%@---之前的位置:%@",NSStringFromCGPoint(currentPoint),NSStringFromCGPoint(prePoint));
    self.transform = CGAffineTransformTranslate(self.transform, offsetX, offsetY);
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"FlyElephant---触摸结束");
}

@end

TouchView *touchView = [[TouchView alloc] initWithFrame:CGRectMake(100, 300, 100, 100)];
    touchView.backgroundColor = [UIColor greenColor];
    [self.view addSubview:touchView];

UIPanGestureRecognizer

初始化视图：

UIView *tagView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
    tagView.backgroundColor = [UIColor redColor];
    self.tagView = tagView;
    [self.view addSubview:self.tagView];

手势状态触摸的过程中有枚举状态可以判断:

typedef NS_ENUM(NSInteger, UIGestureRecognizerState) {
    UIGestureRecognizerStatePossible,   // the recognizer has not yet recognized its gesture, but may be evaluating touch events. this is the default state
    
    UIGestureRecognizerStateBegan,      // the recognizer has received touches recognized as the gesture. the action method will be called at the next turn of the run loop
    UIGestureRecognizerStateChanged,    // the recognizer has received touches recognized as a change to the gesture. the action method will be called at the next turn of the run loop
    UIGestureRecognizerStateEnded,      // the recognizer has received touches recognized as the end of the gesture. the action method will be called at the next turn of the run loop and the recognizer will be reset to UIGestureRecognizerStatePossible
    UIGestureRecognizerStateCancelled,  // the recognizer has received touches resulting in the cancellation of the gesture. the action method will be called at the next turn of the run loop. the recognizer will be reset to UIGestureRecognizerStatePossible
    
    UIGestureRecognizerStateFailed,     // the recognizer has received a touch sequence that can not be recognized as the gesture. the action method will not be called and the recognizer will be reset to UIGestureRecognizerStatePossible
    
    // Discrete Gestures – gesture recognizers that recognize a discrete event but do not report changes (for example, a tap) do not transition through the Began and Changed states and can not fail or be cancelled
    UIGestureRecognizerStateRecognized = UIGestureRecognizerStateEnded // the recognizer has received touches recognized as the gesture. the action method will be called at the next turn of the run loop and the recognizer will be reset to UIGestureRecognizerStatePossible
};

状态过程处理:

- (void)handlePan:(UIPanGestureRecognizer *)recognizer {
    if (recognizer.state == UIGestureRecognizerStateBegan) {
        NSLog(@"FlyElephant---视图拖动开始");
    } else if (recognizer.state == UIGestureRecognizerStateChanged) {
        CGPoint location = [recognizer locationInView:self.view];
        
        if (location.y < 0 || location.y > self.view.bounds.size.height) {
            return;
        }
        CGPoint translation = [recognizer translationInView:self.view];
        
        NSLog(@"当前视图在View的位置:%@----平移位置:%@",NSStringFromCGPoint(location),NSStringFromCGPoint(translation));
        recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x,recognizer.view.center.y + translation.y);
        [recognizer setTranslation:CGPointZero inView:self.view];
        
    } else if (recognizer.state == UIGestureRecognizerStateEnded || recognizer.state == UIGestureRecognizerStateCancelled) {
        NSLog(@"FlyElephant---视图拖动结束");
    }
}