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

@property (nonatomic, weak) UIView *clipView;

- (UIView *)clipView
{
  //如果clipView為被創(chuàng)建，就創(chuàng)建
  if (_clipView == nil)
  {
    UIView *view = [[UIView alloc] init];
    _clipView = view;
    //設(shè)置clipView的背景色和透明度
    view.backgroundColor = [UIColor blackColor];
    view.alpha = 0.5;
    //將clipView添加到控制器的view上，此時(shí)的clipView不會(huì)顯示（未設(shè)置其frame）
    [self.view addSubview:_clipView];
  }
  return _clipView;
}

/**創(chuàng)建手勢(shì)**/
UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
  /**
  *每當(dāng)pan手勢(shì)的位置發(fā)生變化，就會(huì)調(diào)用pan:方法，并將手勢(shì)作為參數(shù)傳遞
  */
/**添加手勢(shì)**/
[self.view addGestureRecognizer:pan];

@property (nonatomic, assign) CGPoint startPoint;

- (void)pan:(UIPanGestureRecognizer *)pan
{
  CGPoint endPoint = CGPointZero;

  if (pan.state == UIGestureRecognizerStateBegan)
  {
    /**開始點(diǎn)擊時(shí)，記錄手勢(shì)的起點(diǎn)**/
    self.startPoint = [pan locationInView:self.view];
  }
  else if(pan.state == UIGestureRecognizerStateChanged)
  {
    /**當(dāng)手勢(shì)移動(dòng)時(shí)，動(dòng)態(tài)改變終點(diǎn)的值，并計(jì)算起點(diǎn)與終點(diǎn)之間的矩形區(qū)域**/
    endPoint = [pan locationInView:self.view];
    //計(jì)算矩形區(qū)域的寬高
    CGFloat w = endPoint.x - self.startPoint.x;
    CGFloat h = endPoint.y - self.startPoint.y;
    //計(jì)算矩形區(qū)域的frame
    CGRect clipRect = CGRectMake(self.startPoint.x, self.startPoint.y, w, h);
    //設(shè)置剪切區(qū)域的frame
    self.clipView.frame = clipRect;
  }
  else if(pan.state == UIGestureRecognizerStateEnded)
  {
    /**若手勢(shì)停止，將剪切區(qū)域的圖片內(nèi)容繪制到圖形上下文中**/
    //開啟位圖上下文
    UIGraphicsBeginImageContextWithOptions(self.imageView.bounds.size, NO, 0);
    //創(chuàng)建大小等于剪切區(qū)域大小的封閉路徑
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.clipView.frame];
    //設(shè)置超出的內(nèi)容不顯示，
    [path addClip];
    //獲取繪圖上下文
    CGContextRef context = UIGraphicsGetCurrentContext();
    //將圖片渲染的上下文中
    [self.imageView.layer renderInContext:context];
    //獲取上下文中的圖片
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    //關(guān)閉位圖上下文
    UIGraphicsEndImageContext();
    //移除剪切區(qū)域視圖控件，并清空
    [self.clipView removeFromSuperview];
    self.clipView = nil;
    //將圖片顯示到imageView上
    self.imageView.image = image;
    //通過alertView提示用戶，是否將圖片保存至相冊(cè)
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"保存圖片" message:@"是否將圖片保存至相冊(cè)？" delegate:self cancelButtonTitle:@"否" otherButtonTitles:@"是", nil];
    [alertView show];
}
}

- (void)alertView:(nonnull UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
  //若點(diǎn)擊了“是”，則保存圖片
  if (buttonIndex == 1)
  {
    UIImageWriteToSavedPhotosAlbum(self.imageView.image, nil, nil, nil);
    /**
    * 該方法可以設(shè)置保存完畢調(diào)用的方法，此處未進(jìn)行設(shè)置
    */
  }
}