title: SDWebImage eager load images
body: <p>I am trying to eager load bunch of images:</p>
  
  <pre><code>for (NSDictionary *s in things) {
      [manager downloadWithURL:[NSURL URLWithString:s[photo]]
                       options:0
                      progress:nil
                     completed:nil];
  }
  </code></pre>
  
  <p>It's not downloading these images. However, if I pass in an empty completion block, like so:</p>
  
  <pre><code>for (NSDictionary *s in things) {
      [manager downloadWithURL:[NSURL URLWithString:s[photo]]
                       options:0
                      progress:nil
                     completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished) { }];
  }
  </code></pre>
  
  <p>then it works just fine. My question is: why? Is there a better way to do this? Passing in an empty block doesn't seem right to me. </p>