協(xié)議內(nèi)容

@protocol WXImageOperationProtocol <NSObject>

- (void)cancel;

@end

@protocol WXImgLoaderProtocol <WXModuleProtocol>

/**
 * @abstract Creates a image download handler with a given URL
 *
 * @param imageUrl The URL of the image to download
 *
 * @param imageFrame  The frame of the image you want to set
 *
 * @param options : The options to be used for this download
 *
 * @param completedBlock : A block called once the download is completed.
 *                 image : the image which has been download to local.
 *                 error : the error which has happened in download.
 *              finished : a Boolean value indicating whether download action has finished.
 */
- (id<WXImageOperationProtocol>)downloadImageWithURL:(NSString *)url imageFrame:(CGRect)imageFrame userInfo:(NSDictionary *)options completed:(void(^)(UIImage *image,  NSError *error, BOOL finished))completedBlock;

@end

使用者1WXNavigationDefaultImpl

if (icon) {
    WXBarButton *button = [WXBarButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(0, 0, 25, 25);
    button.instanceId = param[@"instanceId"];
    button.nodeRef = param[@"nodeRef"];
    button.position = position;
    [button addTarget:self action:@selector(onClickBarButton:) forControlEvents:UIControlEventTouchUpInside];
    
    [[self imageLoader] downloadImageWithURL:icon imageFrame:CGRectMake(0, 0, 25, 25) userInfo:nil completed:^(UIImage *image, NSError *error, BOOL finished) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [button setBackgroundImage:image forState:UIControlStateNormal];
            [button setBackgroundImage:image forState:UIControlStateHighlighted];
        });
    }];
    
    return button;
}

下載button的icon

使用者2WXImageComponent

- (void)updateImage
{
    __weak typeof(self) weakSelf = self;
    dispatch_async(WXImageUpdateQueue, ^{
        [self cancelImage];
        
        void(^downloadFailed)(NSString *, NSError *) = ^void(NSString *url, NSError *error){
            WXLogError(@"Error downloading image:%@, detail:%@", url, [error localizedDescription]);
        };
        
        NSString *imageSrc = weakSelf.imageSrc;
        NSString *placeholderSrc = weakSelf.placeholdSrc;
        
        if (weakSelf.placeholdSrc) {
            WXLogDebug(@"Updating image, component:%@, placeholder:%@ ", self.ref, placeholderSrc);
            weakSelf.placeholderOperation = [[weakSelf imageLoader] downloadImageWithURL:placeholderSrc imageFrame:weakSelf.calculatedFrame userInfo:nil completed:^(UIImage *image, NSError *error, BOOL finished) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    __strong typeof(self) strongSelf = weakSelf;
                    UIImage *viewImage = ((UIImageView *)strongSelf.view).image;
                    if (error) {
                        downloadFailed(placeholderSrc,error);
                        if ([strongSelf isViewLoaded] && !viewImage) {
                            ((UIImageView *)(strongSelf.view)).image = nil;
                        }
                        return;
                    }
                    if (![placeholderSrc isEqualToString:strongSelf.placeholdSrc]) {
                        return;
                    }
                   
                    if ([strongSelf isViewLoaded] && !viewImage) {
                        ((UIImageView *)strongSelf.view).image = image;
                    }
                });
            }];
        }
        if (weakSelf.imageSrc) {
            WXLogDebug(@"Updating image:%@, component:%@", self.imageSrc, self.ref);
            NSDictionary *userInfo = @{@"imageQuality":@(weakSelf.imageQuality), @"imageSharp":@(weakSelf.imageSharp)};
            
            dispatch_async(dispatch_get_main_queue(), ^{
                weakSelf.imageOperation = [[weakSelf imageLoader] downloadImageWithURL:imageSrc imageFrame:weakSelf.calculatedFrame userInfo:userInfo completed:^(UIImage *image, NSError *error, BOOL finished) {
                    dispatch_async(dispatch_get_main_queue(), ^{
                        __strong typeof(self) strongSelf = weakSelf;
                        
                        if (weakSelf.imageLoadEvent) {
                            [strongSelf fireEvent:@"load" params:@{ @"success": error? @"false" : @"true"}];
                        }
                        if (error) {
                            downloadFailed(imageSrc, error);
                            return ;
                        }
                        
                        if (![imageSrc isEqualToString:strongSelf.imageSrc]) {
                            return ;
                        }
                        
                        if ([strongSelf isViewLoaded]) {
                            ((UIImageView *)strongSelf.view).image = image;
                        }
                    });
                }];
            });
        }
        if (!weakSelf.imageSrc && !weakSelf.placeholdSrc) {
            dispatch_async(dispatch_get_main_queue(), ^{
                self.layer.contents = nil;
            });
        }
    });
}

實(shí)現(xiàn)

sdk沒有提供默認(rèn)的實(shí)現(xiàn)，需要自定義實(shí)現(xiàn)方法喇闸。常見的做法是用SDWebImage這個(gè)第三方庫來做

- (id<WXImageOperationProtocol>)downloadImageWithURL:(NSString *)url imageFrame:(CGRect)imageFrame userInfo:(NSDictionary *)userInfo completed:(void(^)(UIImage *image,  NSError *error, BOOL finished))completedBlock {
    return (id<WXImageOperationProtocol>)[[SDWebImageManager sharedManager] downloadImageWithURL:[NSURL URLWithString:url] options:SDWebImageRetryFailed progress:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
        if (completedBlock) {
            completedBlock(image, error, finished);
        }
    }];
}

疑問

1. imageFrame參數(shù)沒有處理蒸眠。一般可以在completed中對(duì)下載得到的圖片進(jìn)行壓縮什么的漾橙。當(dāng)然，只要資源圖片大小合適更好楞卡，不需要處理也行

2. 協(xié)議的返回值沒有具體指定霜运，這里只是進(jìn)行了強(qiáng)制轉(zhuǎn)換。真的要
   取消圖片下載蒋腮，具體該怎么操作需要進(jìn)一步細(xì)化淘捡。只是這種情況用到的比較少

@protocol SDWebImageOperation <NSObject>

- (void)cancel;

@end