来自块的函数返回值 [英] function return value from block

问题描述

如果我有一个返回int的函数并且int的返回值是从块中获取的，怎么办?

What if I have a function that returns an int and the return value of the int is taken from the block?

例如:

- (int) queryForKey:(NSString *)aKey view:(UIButton *)aView countView:(UIView *)aCountView counter:(int) count {
    //some initialization
    [query countObjectsInBackgroundWithBlock:^(int number, NSError * error) {
        [aCountView addSubview:self.generateCountLabel];

        if (number > 0){
            [aView setUserInteractionEnabled:YES];
            [aView setEnabled:YES];
        }
        //return number; //doing this will generate an error
    }];
}

另一个问题是，如果我有一个int作为上面函数的参数传入，我想给它赋一个值怎么办?这样的事情甚至有可能吗?

also another question is, what if I have an int passed in as an argument of the function above and I would like to assign a value to it. Is some thing like that even possible?

推荐答案

问题是您有一个同步方法(一个要立即返回值的方法)，该方法需要返回派生自异步方法(一个用另一种方式处理业务.

The problem is that you have a synchronous method (one that wants to return the value immediately) that needs to return a value derived from an asynchronous method (one that goes about it's business in a different thread).

有几种解决方法:

• 等待countObjectsInBackgroundWithBlock:方法完成，请按照@simonpie所述使用__block模式.

将return number;替换为对生成的数字感兴趣的某个地方的调用.这也意味着queryForKey:view:countView:可能会返回void.

replace the return number; with a call to something somewhere interested in the resulting number. This also means that queryForKey:view:countView: will likely return void.

后者是首选解决方案，因为它不会阻塞调用queryForKey:...方法的线程.

The latter is the preferred solution as it will not block the thread calling the queryForKey:... method.

请注意，除了主线程之外，您不能在任何其他对象上添加UIKit类.如果该块是在后台线程上执行的，则在该块中执行的操作是无效的.

Note that you can't diddle UIKit classes on anything but the main thread. If that block is executed on a background thread, then doing what you are doing in the block is invalid.

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