MessageDialog - 需要等待用户输入 [英] MessageDialog - needs to wait for user input

问题描述

我有实例化的同步方法事件的视图模型。该事件信号的UI，我们继续之前，需要一个是或否从用户的答案。

I have a ViewModel which instantiates an event in a synchronous method. The event signals to the UI that we need a "Yes" or "No" answer from the user before continuing.

我想显示 MessageDialog 并等待用户提供了一个答案 - 是或否。我有困难的时候这样做。目前，我得到一个 UnauthorizedAccessException 试图做到这一点的时候。

I am trying to display a MessageDialog and wait until the user provides an answer - Yes or No. I am having a difficult time doing this. I currently get an UnauthorizedAccessException when trying to do this.

下面就一起来看看UI中的code：

Here's a look at the code in the UI:

async Task<bool> Instance_SwitchConfirmation(string question)
{
    MessageDialog md = new MessageDialog(question);
    md.Commands.Add(new UICommand("Yes", CommandInvokedHandler));
    md.Commands.Add(new UICommand("No", CommandInvokedHandler));
    md.ShowAsync();

    return this.canSwitch;
}

async void CommandInvokedHandler(IUICommand command)
{
    this.canSwitch = command.Label == "Yes" ? true : false;
}

我曾尝试：

var uiContext = TaskScheduler.FromCurrentSynchronizationContext();
Task.Factory.StartNew(() => {
    MessageDialog md = new MessageDialog(question);
    md.Commands.Add(new UICommand("Yes", CommandInvokedHandler));
    md.Commands.Add(new UICommand("No", CommandInvokedHandler));
    md.ShowAsync();
}, 
new System.Threading.CancellationToken(), 
TaskCreationOptions.PreferFairness, uiContext);

但这种失败，出现相同的异常。

but this fails with the same exception.

最后，如果我只是等待MessageDialog像这样，不显示对话框，并在UI线程锁定。

Lastly, if I simply await the MessageDialog like so, the dialog is not displayed and the UI thread locks up.

MessageDialog md = new MessageDialog(question);
md.Commands.Add(new UICommand("Yes", CommandInvokedHandler));
md.Commands.Add(new UICommand("No", CommandInvokedHandler));
await md.ShowAsync();

如果 MessageDialog 不得不的同步版本放映（）我会被罚款，但的asynchrnous behvaior MessageDialog 再加上我synchrounous套路，加上跨线程是混淆了我。我想知道，如果有人可以勾勒出什么，我需要做的等待在 MessageDialog 之前，我的后端视图模型继续同步方法。

If MessageDialog had a synchronous version of Show() I would be fine but the asynchrnous behvaior of MessageDialog coupled with my synchrounous routine, coupled with cross threading is confusing me. I'm wondering if someone can outline what I need to do to wait for user input on a MessageDialog before continuing a synchronous method in my backend ViewModel.

在此先感谢您的帮助。

推荐答案

请参阅Win8 C＃地铁调度员和RPC_E_WRONG_THREAD 和<一个href=\"http://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.core.coredispatcher.runasync\"><$c$c>CoreDispatcher.RunAsync.

由于你的方法是不是在调度执行你将需要手动调用code就可以了。为了避免重构为一个回调格局可以使用<一个href=\"http://msdn.microsoft.com/en-us/library/dd449174.aspx\"><$c$c>TaskCompletionSource(T)设置的结果，其结果被设定后后台线程将继续

Since your method isn't executing on the Dispatcher you're going to need to invoke the code on it manually. In order to avoid refactoring into a callback pattern you can use a TaskCompletionSource(T) to set the result and the background thread will continue after the result is set.

var tcs = new TaskCompletionSource<bool>();
var dialogTask = tcs.Task;

MessageDialog md = new MessageDialog(question);
md.Commands.Add(new UICommand("Yes"));
md.Commands.Add(new UICommand("No"));

Dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () => {
    var result = await md.ShowAsync();
    var canSwitch = result.Label == "Yes";
    tcs.SetResult(canSwitch);
});

var result = await dialogTask;
return result;

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