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"]];

如果我想用效果（可能是褪色）替换图像怎么样？

这是因为我想用很多图像制作幻灯片。

Answer 1

您可以与提供块animateWithDuration的再现一起使用，例如setImageWithURLsuccess

[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，您可能希望通过以下方式进行交叉溶解transitionWithView：

[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，如果您担心图像视图（如果您指self的是 视图或视图控制器）在下载完成之前会一直保留，您可以：

__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，图像视图也会保留到下载完成，因此您也可以选择取消dealloc视图控制器方法中正在进行的任何下载：

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

    [_imageView cancelImageRequestOperation];
}

Answer 2

当在线请求成功完成时，尝试将 imageView 的 alpha 从 0 设置为 1：

// You should not call an ivar from a block (so get a weak reference to the imageView)
__weak UIImageView *weakImageView = self.imageView;

// The AFNetworking method to call
[imageView setImageWithURLRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://host.com/image1.png"]] placeholderImage:nil] 
                   success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image){ 
                     // Here you can animate the alpha of the imageview from 0.0 to 1.0 in 0.3 seconds
                     [weakImageView setAlpha:0.0];
                     [UIView beginAnimations:nil context:NULL];
                     [UIView setAnimationDuration:0.3];
                     [weakImageView setAlpha:1.0];
                     [UIView commitAnimations];
                   }
                   failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error){
                     // Your failure handle code     
                   }

当然，您可以在完成块中使用您喜欢的任何其他动画！