从Dispatcher.RunAsync()返回值到后台线程

问题描述

我正在使用Dispatcher.RunAsync()从后台线程显示MessageDialog.但是我很难弄清楚如何返回结果.

I'm using Dispatcher.RunAsync() to show a MessageDialog from a background thread. But I'm having trouble figuring out how to get a result returned.

我的代码:

            bool response = false;

        await dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal,
             async () =>
             {
                 DebugWriteln("Showing confirmation dialog: '" + s + "'.");
                 MessageDialog dialog = new MessageDialog(s);

                 dialog.Commands.Add(new UICommand(GetLanguageString("Util_DialogButtonYes"), new UICommandInvokedHandler((command) => {
                     DebugWriteln("User clicked 'Yes' in confirmation dialog");
                     response = true;
                 })));

                 dialog.Commands.Add(new UICommand(GetLanguageString("Util_DialogButtonNo"), new UICommandInvokedHandler((command) =>
                 {
                     DebugWriteln("User clicked 'No' in confirmatoin dialog");
                     response = false;
                 })));
                 dialog.CancelCommandIndex = 1;
                 await dialog.ShowAsync();
             });
        //response is always False
        DebugWriteln(response);

反正有这样做吗?我考虑过也许可以从RunAsync()内部返回值，但函数无效.

Is there anyway to do it like this?I thought about maybe returning the value from inside RunAsync() but function is void.

推荐答案

您可以使用 ManualResetEvent 类.

这是我的帮助方法，用于将值从UI线程返回到其他线程.这是针对Silverlight的！因此，您可能不能将其复制粘贴到您的应用程序中并期望它能正常工作，但希望它能给您一个思路如何进行.

This is my helper method for returning values from the UI thread to other threads. This is for Silverlight! As such, you probably can't copy-paste it to your application and expect it to work, BUT hopefully it'll give you an idea on how to proceed.

    public static T Invoke<T>(Func<T> action)
    {
        if (Dispatcher.CheckAccess())
            return action();
        else
        {
            T result = default(T);
            ManualResetEvent reset = new ManualResetEvent(false);
            Dispatcher.BeginInvoke(() =>
            {
                result = action();
                reset.Set();
            });
            reset.WaitOne();
            return result;
        }
    }

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