ios - 完成一个街区后返回？

Question

给定以下代码:

+(Tag *) addNewTagwithName:(NSString *)tagName Error:(NSError **)addError {
    AppDelegate *delegate = (AppDelegate *) [[UIApplication sharedApplication]delegate];

    Tag *newTag = [NSEntityDescription insertNewObjectForEntityForName:@"Tag" inManagedObjectContext:delegate.managedObjectContext];
    newTag.tagName = tagName;

    //no error save to parse
    PFObject *tag = [PFObject objectWithClassName:@"Tag"];
    tag[@"tagName"] = newTag.tagName;

    [tag saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
        if(error) {
            *addError = error;
        } else {
            dispatch_async(dispatch_get_main_queue(), ^{
                NSError *error = nil;
                newTag.tagId = tag.objectId;

                if(![delegate.managedObjectContext save:&error]) {
                    *addError = error;
                }

            });

        }
    }];

    return newTag;

}

有哪些方法可以确保仅在执行 newTag.tagId = tag.objectId 后才返回 newTag？

Answer 1

这是不可能的。因为 addNewTagwithName: 方法会立即返回，但完成 block 将在稍后执行并且它什么都没有。

更新:试试下面的代码...

+(void) addNewTagwithName:(NSString *)tagName Error:(NSError **)addError completionBlock:(CompletionBlock)comBlock {

    //no error save to parse
    PFObject *tag = [PFObject objectWithClassName:@"Tag"];
    tag[@"tagName"] = tagName;

    [tag saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
        if(error) {
            *addError = error;
        } else {
            dispatch_async(dispatch_get_main_queue(), ^{
                comBlock(succeeded,error);
                if(![delegate.managedObjectContext save:&error]) {
                    *addError = error;
                }
            });
        }
    }];
}

你的方法调用应该是。

CompletionBlock currentTagBlock = ^(BOOL succeeded, NSError *error){
      AppDelegate *delegate = (AppDelegate *) [[UIApplication sharedApplication]delegate];

      Tag *newTag = [NSEntityDescription insertNewObjectForEntityForName:@"Tag" inManagedObjectContext:delegate.managedObjectContext];
    newTag.tagName = tagName;
      if(!error);
         newTag.tagId = tag.objectId;
      /* Here you should write your code using tag
        ex: [self processWithNewTag:newTag]; */

};
[Tag addNewTagwithName:tagName Error:&addError completionBlock:currentTagBlock];