微信图片点击放大效果

1.通过上下文获取当前图片
2.动态添加一个UIImageView
3.计算目标位置的frame 做属性动画
4.动画完毕移除imageVIew,创建对应的图片查看器(未实现)

UIGraphicsBeginImageContextWithOptions(self.imageView.bounds.size, YES, 0);
    [self.imageView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
    UIImageView * coverView = [[UIImageView alloc] initWithImage:image];
    coverView.frame = self.imageView.frame;
    [self.view addSubview:coverView];
    CGFloat w = [UIScreen mainScreen].bounds.size.width;
    CGFloat h = w / coverView.bounds.size.width * coverView.bounds.size.height;
     [UIView animateWithDuration:4 animations:^{
         coverView.frame = CGRectMake(([UIScreen mainScreen].bounds.size.width - w) * 0.5, ([UIScreen mainScreen].bounds.size.height - h) * 0.5, w, h);
     } completion:^(BOOL finished) {
         [coverView removeFromSuperview];
     }];