如何从后台线程返回数据? [英] How to return data from background thread ?

问题描述

我有一个方法，应该返回一个在后台线程中填充的数组.我想等return语句，直到数组完全填充为止.我该怎么做?我知道如何处理没有返回类型的数据，但是我想调用此函数并获取填充的数组.

I have a method that should return an array which is populated in a background thread. I would like to wait with the return statement until the array is completely populated. How would I do that ? I know how to process data with no return type, but I would like to call this function and get the populated array.

示例(这里的数组最终为空，因为它在填充数组之前就返回了-我想做一些事情来返回填充的数组):

Example (Here the array ends up empty because it returns before array is populated - I would like to do something to return the populated array) :

-(NSArray*)fetchSomeArray{

    __block NSArray *arrayToReturn;

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,(unsigned long)NULL), ^(void) {

        NSArray *someArray = ...; // getting some array from database
        arrayToReturn = [NSMutableArray new];

        for(int i=0;i<someArray.count;i++){

            [arrayToReturn addObject:...];
        }

    });

    return arrayToReturn;

}

推荐答案

使用委托，或阻止并取出return arrayToReturn;.在"for"之后并在"dispatch_async"内部:

Use delegation, or blocks and take out the return arrayToReturn;. After your "for" and inside the "dispatch_async":

dispatch_async(dispatch_get_main_queue(),^{
      [myDelegate passComputedArray:arrayToReturn];
});

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