NSURL *url = [NSURL URLWithString:@"http://i0.kym-cdn.com/entries/icons/original/000/005/545/OpoQQ.jpg?1302279173"];
NSData *data = [NSData dataWithContentsOfURL:url];
imageView.image = [[[UIImage imageWithData:data];
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我想在下载时设置进度条.