UITouch触摸事件处理

UIViewController继承自UIResponder
UIResponder中针对触摸事件声明了4个主要方法：

//当点击屏幕的开始瞬间调用此方法
- (void)touchesBegan:(NSSet *)touches withEvent:(nullable UIEvent *)event;
//手指在屏幕上时调用（包括滑动）
- (void)touchesMoved:(NSSet *)touches withEvent:(nullable UIEvent *)event;
//手指离开屏幕时调用
- (void)touchesEnded:(NSSet *)touches withEvent:(nullable UIEvent *)event;
//特殊情况中断触屏事件时调用，例如电话中断了游戏
- (void)touchesCancelled:(NSSet *)touches withEvent:(nullable UIEvent *)event;

根据以上四个方法，设计一个图片视图随手指触屏事件变化的例子：
ViewController.m

- (void)viewDidLoad {
    [super viewDidLoad];

    UIImage *image = [UIImage imageNamed:@"icon1"];
    UIImageView *iView = [[UIImageView alloc]initWithImage:image];
    iView.frame = CGRectMake(50, 100, 220, 300);
    iView.tag =101;
    [self.view addSubview:iView];
}

//当点击屏幕的开始瞬间调用此方法
//一次点击的过程
//1，手指触碰屏幕 touchesBegan
//2，手指接触到屏幕并且没有离开，按住屏幕时（包括滑动）
//3，手指离开屏幕的瞬间
- (void)touchesBegan:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    
    //获取点击对象，anyObject获取任何一个点击对象
    //只有一个点击对象，获得的对象就是点击对象
    UITouch* touch = [touches anyObject];
    if(touch.tapCount == 1){
        NSLog(@"单次点击");
    }
    else if(touch.tapCount == 2){
        NSLog(@"双次点击");
    }
    
    NSLog(@"手指触碰瞬间");
    _lastPoint = [touch locationInView:self.view];
    
}
//手指在屏幕上时调用
- (void)touchesMoved:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    UITouch *touch = [touches anyObject];
    
    CGPoint pt = [touch locationInView:self.view];
    NSLog(@"x = %f, y = %f",pt.x,pt.y);
    //每次移动的偏移量
    float xOffset = pt.x -_lastPoint.x;
    float yOffset = pt.y - _lastPoint.y;
    UIImageView *iView = (UIImageView*)[self.view viewWithTag:101];
    iView.frame = CGRectMake(iView.frame.origin.x+xOffset, iView.frame.origin.y+yOffset, iView.frame.size.width, iView.frame.size.height);
    _lastPoint = pt;
    //NSLog(@"手指滑动");
}
//手指离开屏幕时
- (void)touchesEnded:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    NSLog(@"手指离开屏幕");
}
//特殊情况中断触屏事件时调用，例如电话中断了游戏
- (void)touchesCancelled:(NSSet *)touches withEvent:(nullable UIEvent *)event{
    
}