UIImageview 顯示網絡圖片及問題

    //同步加載

//    [imageview setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:annotation.subtitle]]]];

    //異步加載

//    [imageview sd_setImageWithURL:[NSURL URLWithString:annotation.subtitle] placeholderImage:[UIImage imageNamed:@"placehodeLoading.png"]];

//異步加載圖片不顯示問題

     [imageview sd_setImageWithURL:[NSURL URLWithString:annotation.subtitle] placeholderImage:[UIImage imageNamed:@"placehodeLoading.png"] options:SDWebImageLowPriority | SDWebImageRetryFailed];