weex并没有提供图片下载的能力，所以就要我们在native端来实现。所以顺便讲一下如何加载本地图片。

一、网络图片

1、创建一个继承自NSObject的类
2、pod 导入SDWebImage(使用这个库下载图片)
2、实现WXImgLoaderProtocol
3、具体实现如下

- (id<WXImageOperationProtocol>)downloadImageWithURL:(NSString *)url imageFrame:(CGRect)imageFrame userInfo:(NSDictionary *)options completed:(void (^)(UIImage *, NSError *, BOOL))completedBlock
{
    if (![self isValidString:url]) {
        return nil;
    }
        if ([url hasPrefix:@"//"]) {
        url = [@"http:" stringByAppendingString:url];
    }
    
    SDWebImageManager *mgr = [SDWebImageManager sharedManager];
    
    id op = [mgr 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);
                                }
                            }];
    return (id<WXImageOperationProtocol>)op;
}

- (BOOL)isValidString:(NSString *)str
{
    if (str && [str isKindOfClass:[NSString class]] && [str length] > 0) {
        return YES;
    }
    
    return NO;
}

其实官网都说的听清楚了，照着来基本上问题都不大。下面再说说如何实现加载本地图片

二、本地图片

在上面的基础上
实现的方式也是比较简单，网络图片是下载好图片回调给weex显示，本地是不是也可以 加载好本地的回调给weex显示，具体实现看一下代码大家瞬间就明白了。

- (id<WXImageOperationProtocol>)downloadImageWithURL:(NSString *)url imageFrame:(CGRect)imageFrame userInfo:(NSDictionary *)options completed:(void (^)(UIImage *, NSError *, BOOL))completedBlock
{
    if (![self isValidString:url]) {
        return nil;
    }
    //实现加载xcassets 本地资源文件
    if ([url hasPrefix:@"assets:"]) {
        UIImage *image = [UIImage imageNamed:[url substringFromIndex:7]];
        completedBlock(image, nil, YES);
        return (id<WXImageOperationProtocol>)[NSObject new];
    }
    if ([url hasPrefix:@"//"]) {
        url = [@"http:" stringByAppendingString:url];
    }
    
    SDWebImageManager *mgr = [SDWebImageManager sharedManager];
    
    id op = [mgr 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);
                                }
                            }];
    return (id<WXImageOperationProtocol>)op;
}

- (BOOL)isValidString:(NSString *)str
{
    if (str && [str isKindOfClass:[NSString class]] && [str length] > 0) {
        return YES;
    }
    
    return NO;
}

JS中只需要写好前缀就可以了。看代码

    <image class="soureImageStyle" src="assets:moren2"/>

demo 下的downloadImageDemo工程 vue文件也在项目路径下。