objective-c - UIImageView+AFNetworking setImageWithURL 带动画

Question

使用 AFNetworking，从服务器下载图像并放入 UIImageView 非常简单:

[imageView setImageWithURL:[NSURL URLWithString:@"http://i.imgur.com/r4uwx.jpg"] placeholderImage:[UIImage imageNamed:@"placeholder-avatar"]];

如果我想用一种效果(可能是淡入淡出)来替换图像呢？？？

因为我想制作一个有很多图片的幻灯片。

Answer 1

您可以将 animateWithDuration 与提供 success block 的 setImageWithURL 的呈现结合使用，例如

[imageView setImageWithURL:[NSURL URLWithString:@"http://i.imgur.com/r4uwx.jpg"] 
          placeholderImage:[UIImage imageNamed:@"placeholder-avatar"]
                   success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                       self.imageView.alpha = 0.0;
                       self.imageView.image = image;
                       [UIView animateWithDuration:0.25
                                        animations:^{
                                            self.imageView.alpha = 1.0;
                                        }];
                   }
                   failure:NULL];

或者，如果您的占位符图像不是空白，您可能希望通过 transitionWithView 交叉溶解:

[imageView setImageWithURL:[NSURL URLWithString:@"http://i.imgur.com/r4uwx.jpg"] 
          placeholderImage:[UIImage imageNamed:@"placeholder-avatar"]
                   success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                       [UIView transitionWithView:self.imageView
                                         duration:0.3
                                          options:UIViewAnimationOptionTransitionCrossDissolve
                                       animations:^{
                                           self.imageView.image = image;
                                       }
                                       completion:NULL];
                   }
                   failure:NULL];

---

更新:

顺便说一句，如果您担心 ImageView (如果您指的是 self、 View 或 View Controller )在下载完成之前一直保留，你可以:

__weak UIImageView *weakImageView = self.imageView;
[imageView setImageWithURL:[NSURL URLWithString:@"http://i.imgur.com/r4uwx.jpg"] 
          placeholderImage:[UIImage imageNamed:@"placeholder-avatar"]
                   success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                       UIImageView *strongImageView = weakImageView; // make local strong reference to protect against race conditions
                       if (!strongImageView) return;

                       [UIView transitionWithView:strongImageView
                                         duration:0.3
                                          options:UIViewAnimationOptionTransitionCrossDissolve
                                       animations:^{
                                           strongImageView.image = image;
                                       }
                                       completion:NULL];
                   }
                   failure:NULL];

即使您这样做了， ImageView 也会保留到下载完成，因此您也可以选择在 View Controller 的 dealloc 方法中取消任何正在进行的下载:

- (void)dealloc
{
    // if MRC, call [super dealloc], too

    [_imageView cancelImageRequestOperation];
}