等待assetForURL块完成

问题描述

我想等待这段代码在继续之前执行，但由于这些块被异步调用，我不知道怎么办???

I would like to wait this code to be executed before to continue but as these blocks are called assynchronously I don't know how to do???

NSURL *asseturl;
NSMutableArray *tmpListAsset = [[NSMutableArray alloc] init];

ALAssetsLibrary *library = [[[ALAssetsLibrary alloc] init] autorelease];
NSMutableArray *objectsToRemove = [[NSMutableArray alloc] init];
for (NSDictionary *dico in assetsList) {
    asseturl = [NSURL URLWithString:[dico objectForKey:@"assetUrl"]];
    NSLog(@"asset url %@", asseturl);
    // Try to load asset at mediaURL
    [library assetForURL:asseturl resultBlock:^(ALAsset *asset) {
        // If asset doesn't exists
        if (!asset){
            [objectsToRemove addObject:dico];
        }else{
            [tmpListAsset addObject:[asseturl absoluteString]];
            NSLog(@"tmpListAsset : %@", tmpListAsset);
        }
    } failureBlock:^(NSError *error) {
        // Type your code here for failure (when user doesn't allow location in your app)
    }];
}

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