如何更新任务完成块中的UI？ [英] How to update UI in a task completion block?

问题描述

在我的应用程序中，我让一个进度指示器开始动画，然后我发送一个HTTP请求。
完成处理程序在块中定义。在得到响应数据后，我隐藏了块内部的进度指示器。我的问题是，我知道，UI更新必须在主线程中执行。

In my application, I let a progress indicator starts animation before I send a HTTP request. The completion handler is defined in a block. After I get the response data, I hide the progress indicator from inside the block. My question is, as I know, UI updates must be performed in the main thread. How can I make sure it?

如果我在窗口控制器中定义一个更新UI的方法，并让块调用方法而不是直接更新UI，解决方案？

If I define a method in the window controller which updates UI, and let the block calls the method instead of updating UI directly, is it a solution?

推荐答案

此外，如果您的应用程序目标iOS> = 4，您可以使用Grand Central Dispatch：

Also, if your app targets iOS >= 4 you can use Grand Central Dispatch:

dispatch_async(dispatch_get_main_queue(), ^{
    // This block will be executed asynchronously on the main thread.
});

这是非常有用的，当你的自定义逻辑不能轻易地用单选择器和对象参数表示 executeSelect ... 方法。

This is useful when your custom logic cannot easily be expressed with the single selector and object arguments that the performSelect… methods take.

要同步执行一个块，使用 dispatch_sync code> - 但确保你当前没有在主队列上执行或GCD会死锁。

To execute a block synchronously, use dispatch_sync() – but make sure you’re not currently executing on the main queue or GCD will deadlock.

__block NSInteger alertResult; // The __block modifier makes alertResult writable
                               // from a referencing block.
void (^ getResponse)() = ^{
    NSAlert *alert = …;
    alertResult = [NSAlert runModal];
};

if ([NSThread isMainThread]) {
    // We're currently executing on the main thread.
    // We can execute the block directly.
    getResponse();
} else {
    dispatch_sync(dispatch_get_main_queue(), getResponse);
}

// Check the user response.
if (alertResult == …) {
    …
}

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