如何从完成块中检索返回值？ [英] How can I retrieve a return value from a completion block?

问题描述

是否可以在主线程上运行完成块？

Is it possible to run a completion block on the main thread?

例如，我有一个方法返回一个值：

For example, I have one method which returns a value:

- (int)test
{

    /* here one method is called with completion block with return type void */

    [obj somemethodwithcompeltionblock:
      {
         /* here I am getting my Int which I want to return */
      }
      ];
}

但是我看不到如何从完成内返回整数值阻止作为此方法的结果，因为完成块在后台线程上运行。

but I can't see how to return the integer value from within the completion block as the result of this method, because the completion block runs on a background thread.

我该怎么做？

推荐答案

您缺少一些关于使用块进行异步开发的基础知识。除了自己的范围之外，您不能从任何地方返回调度块。将每个块视为自己的方法，而不是内联代码。

You're missing some basics about asynchronous development with blocks. You can't have a dispatched block return from anywhere but its own scope. Think of each block as its own method, instead of inline code.

我认为您正在寻找的东西与此类似......

I think what you're looking for is something similar to this...

- (void)testWithHandler:(void(^)(int result))handler
{
    [obj somemethodwithcompeltionblock:^{
            int someInt = 10;
            dispatch_async(dispatch_get_main_queue(), ^{
                handler(10);
            });
      }
      ];
}


- (void)callSite
{
    [self testWithHandler:^(int testResult){
        NSLog(@"Result was %d", testResult);
    }];
}

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