判断图片是否缓存 NSURL *url = [NSURL URLWithString:[model.content objectForKey:@"image"]];            //请求网络地址数据的同步方法            //因为这个方法在子线程(全局队列)中执行,所以不需要考虑死线程的问题            SDWebImageManager *manager = [SDWebImageManager sharedManager];             [manager diskImageExistsForURL:url];            if ([manager diskImageExistsForURL:url]) {                LOG(@"11111")                self.speakImage = [[manager imageCache] imageFromDiskCacheForKey:url.absoluteString];            }else{                LOG(@"3333333")                NSData *data = [NSData dataWithContentsOfURL:url];                self.speakImage = [UIImage imageWithData:data];            }

/**  

获取网络图片的Size, 先通过文件头来获取图片大小  

如果失败 会下载完整的图片Data 来计算大小 所以最好别放在主线程 

如果你有使用SDWebImage就会先看下 SDWebImage有缓存过改图片没有 

支持文件头大小的格式 png、gif、jpg   

*/ 

+(CGSize)downloadImageSizeWithURL:(id)imageURL;

//讨厌警告-(id)diskImageDataBySearchingAllPathsForKey:(id)key{return nil;}+(CGSize)downloadImageSizeWithURL:(id)imageURL{    NSURL* URL = nil;    if([imageURL isKindOfClass:[NSURL class]]){        URL = imageURL;    }    if([imageURL isKindOfClass:[NSString class]]){        URL = [NSURL URLWithString:imageURL];    }    if(URL == nil)        return CGSizeZero;         NSString* absoluteString = URL.absoluteString;     #ifdef dispatch_main_sync_safe    if([[SDImageCache sharedImageCache] diskImageExistsWithKey:absoluteString])    {        UIImage* image = [[SDImageCache sharedImageCache] imageFromMemoryCacheForKey:absoluteString];        if(!image)        {            NSData* data = [[SDImageCache sharedImageCache] performSelector:@selector(diskImageDataBySearchingAllPathsForKey:) withObject:URL.absoluteString];            image = [UIImage imageWithData:data];        }        if(!image)        {            return image.size;        }    }#endif         NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:URL];    NSString* pathExtendsion = [URL.pathExtension lowercaseString];         CGSize size = CGSizeZero;    if([pathExtendsion isEqualToString:@"png"]){        size =  [self downloadPNGImageSizeWithRequest:request];    }    else if([pathExtendsion isEqual:@"gif"])    {        size =  [self downloadGIFImageSizeWithRequest:request];    }    else{        size = [self downloadJPGImageSizeWithRequest:request];    }    if(CGSizeEqualToSize(CGSizeZero, size))    {        NSData* data = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:URL] returningResponse:nil error:nil];        UIImage* image = [UIImage imageWithData:data];        if(image)        {#ifdef dispatch_main_sync_safe            [[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:YES imageData:data forKey:URL.absoluteString toDisk:YES];#endif            size = image.size;        }    }    return size;}+(CGSize)downloadPNGImageSizeWithRequest:(NSMutableURLRequest*)request{    [request setValue:@"bytes=16-23" forHTTPHeaderField:@"Range"];    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];    if(data.length == 8)    {        int w1 = 0, w2 = 0, w3 = 0, w4 = 0;        [data getBytes:&w1; range:NSMakeRange(0, 1)];        [data getBytes:&w2; range:NSMakeRange(1, 1)];        [data getBytes:&w3; range:NSMakeRange(2, 1)];        [data getBytes:&w4; range:NSMakeRange(3, 1)];        int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;        int h1 = 0, h2 = 0, h3 = 0, h4 = 0;        [data getBytes:&h1; range:NSMakeRange(4, 1)];        [data getBytes:&h2; range:NSMakeRange(5, 1)];        [data getBytes:&h3; range:NSMakeRange(6, 1)];        [data getBytes:&h4; range:NSMakeRange(7, 1)];        int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;        return CGSizeMake(w, h);    }    return CGSizeZero;}+(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request{    [request setValue:@"bytes=6-9" forHTTPHeaderField:@"Range"];    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];    if(data.length == 4)    {        short w1 = 0, w2 = 0;        [data getBytes:&w1; range:NSMakeRange(0, 1)];        [data getBytes:&w2; range:NSMakeRange(1, 1)];        short w = w1 + (w2 << 8);        short h1 = 0, h2 = 0;        [data getBytes:&h1; range:NSMakeRange(2, 1)];        [data getBytes:&h2; range:NSMakeRange(3, 1)];        short h = h1 + (h2 << 8);        return CGSizeMake(w, h);    }    return CGSizeZero;}+(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request{    [request setValue:@"bytes=0-209" forHTTPHeaderField:@"Range"];    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];         if ([data length] <= 0x58) {        return CGSizeZero;    }         if ([data length] < 210) {// 肯定只有一个DQT字段        short w1 = 0, w2 = 0;        [data getBytes:&w1; range:NSMakeRange(0x60, 0x1)];        [data getBytes:&w2; range:NSMakeRange(0x61, 0x1)];        short w = (w1 << 8) + w2;        short h1 = 0, h2 = 0;        [data getBytes:&h1; range:NSMakeRange(0x5e, 0x1)];        [data getBytes:&h2; range:NSMakeRange(0x5f, 0x1)];        short h = (h1 << 8) + h2;        return CGSizeMake(w, h);    } else {        short word = 0x0;        [data getBytes:&word; range:NSMakeRange(0x15, 0x1)];        if (word == 0xdb) {            [data getBytes:&word; range:NSMakeRange(0x5a, 0x1)];            if (word == 0xdb) {// 两个DQT字段                short w1 = 0, w2 = 0;                [data getBytes:&w1; range:NSMakeRange(0xa5, 0x1)];                [data getBytes:&w2; range:NSMakeRange(0xa6, 0x1)];                short w = (w1 << 8) + w2;                short h1 = 0, h2 = 0;                [data getBytes:&h1; range:NSMakeRange(0xa3, 0x1)];                [data getBytes:&h2; range:NSMakeRange(0xa4, 0x1)];                short h = (h1 << 8) + h2;                return CGSizeMake(w, h);            } else {// 一个DQT字段                short w1 = 0, w2 = 0;                [data getBytes:&w1; range:NSMakeRange(0x60, 0x1)];                [data getBytes:&w2; range:NSMakeRange(0x61, 0x1)];                short w = (w1 << 8) + w2;                short h1 = 0, h2 = 0;                [data getBytes:&h1; range:NSMakeRange(0x5e, 0x1)];                [data getBytes:&h2; range:NSMakeRange(0x5f, 0x1)];                short h = (h1 << 8) + h2;                return CGSizeMake(w, h);            }        } else {            return CGSizeZero;        }    }}