Cocoa touch 在后台实现一个块，然后在完成后在主线程上运行另一个块？

如何实现以下块

我需要在后台运行一些任务。 然后后台任务完成后，一些任务将在主线程中运行

之所以使用块，是因为我需要更新传递到此方法中的视图

- (void)doALongTask:(UIView *)someView {

    [self doSomethingInBackground:^{

        // Runs some method in background, while foreground does some animation.
        [self doSomeTasksHere];

    } completion:^{

        // After the task in background is completed, then run more tasks.
        [self doSomeOtherTasksHere];

        [someView blahblah];

    }];
} 

还是有更简单的方法来实现这一点？

---

谢谢。

我不确定您是否在询问块是如何工作的，或者如何在主线程上运行完成处理程序

根据您的代码，您正在调用doSomethingInBackground并将两个块作为参数传入。必须在doSomethingInBackground方法中调用这些块才能运行。doSomethingBackground必须看起来像这样：

-(void)doSomethingInBackground:(void (^))block1 completion:(void (^))completion
{
    // do whatever you want here

    // when you are ready, invoke the block1 code like this
    block1();

    // when this method is done call the completion handler like this
    completion();
}

- (void)doALongTask:(UIView *)someView {

    [self doSomethingInBackground:^{

        // Runs some method in background, while foreground does some animation.
        [self doSomeTasksHere];

    } completion:^{
        // After the task in background is completed, then run more tasks.
        dispatch_async(dispatch_get_main_queue(), ^{
            [self doSomeOtherTasksHere];
            [someView blahblah];
        });
    }];
}

现在，如果要确保完成处理程序在主线程上运行，请将代码更改为如下所示：

-(void)doSomethingInBackground:(void (^))block1 completion:(void (^))completion
{
    // do whatever you want here

    // when you are ready, invoke the block1 code like this
    block1();

    // when this method is done call the completion handler like this
    completion();
}

- (void)doALongTask:(UIView *)someView {

    [self doSomethingInBackground:^{

        // Runs some method in background, while foreground does some animation.
        [self doSomeTasksHere];

    } completion:^{
        // After the task in background is completed, then run more tasks.
        dispatch_async(dispatch_get_main_queue(), ^{
            [self doSomeOtherTasksHere];
            [someView blahblah];
        });
    }];
}

这是我根据你写的代码得出的答案

但是，如果此注释“我需要在后台运行一些任务。然后在后台任务完成后，一些任务将在主线程中运行”更能说明您实际尝试执行的操作，那么您只需执行以下操作：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // do your background tasks here
    [self doSomethingInBackground];

    // when that method finishes you can run whatever you need to on the main thread
    dispatch_async(dispatch_get_main_queue(), ^{
        [self doSomethingInMainThread];
    });
});

---

你的问题是什么？如何实现

doSomethingInBackground:completion:

，以便在主线程上调用完成处理程序？如果有其他/更简单的实施方式……在您的问题中，“这”意味着什么？