C# e、 在UWP中等待异步对话框后无法设置取消

这是针对Windows 10 UWP应用程序的。当用户试图离开页面时，我想让用户确认是否要保存当前数据

我已经覆盖了如下所示的OnNavigatingFrom。但是，在异步消息对话框之后，设置

e.Cancel=false

不起作用。即使

e.Cancel

稍后设置为false，该页面仍保留在当前页面上。请帮忙

protected override async void OnNavigatingFrom(NavigatingCancelEventArgs e)

{
    e.Cancel = true; //if I don't put this at the top, the page navigates right away

    var yesCommand = new UICommand("Yes", async cmd => {

        try
        {
            await SaveWorkshetItem(false);
            e.Cancel = false;
        }
        catch (Exception ex)
        {
            await new MessageDialog("Error saving Worksheet Item. Please contact you administrator." + ex.Message + Environment.NewLine + ex.StackTrace).ShowAsync();
        }

    });

    var noCommand = new UICommand("No", cmd => { e.Cancel = false; });

    var cancelCommand = new UICommand("Cancel", cmd => { e.Cancel = true;  });

    var dialog = new MessageDialog("Do you want to save the current item before navigating away?");
    dialog.Options = MessageDialogOptions.None;
    dialog.Commands.Add(yesCommand);

    dialog.Commands.Add(noCommand);
    dialog.Commands.Add(cancelCommand);

    await dialog.ShowAsync();

    base.OnNavigatingFrom(e);

}

为了简化这一点，下面的代码使页面永远不会离开，即使我在示例

消息对话框之后更改回
e.Cancel=false

protected override async void OnNavigatingFrom(NavigatingCancelEventArgs e)

{
    e.Cancel = true; //if I don't put this at the top, the page navigates right away

    await new MessageDialog("Do you want to save the current item before navigating away?").ShowAsync();

    e.Cancel = false;  //unconditionally setting this back to false and it still won't leave the page

    base.OnNavigatingFrom(e);
}

要自己处理导航，请设置Cancel=true（正如您已经做的那样），然后打开对话框以获取用户输入。一旦知道用户的选择，如果用户决定允许进行导航，请使用导航API（例如Frame.GoBack）执行所需的导航（基于例如NavigationMode）

以下是一些基本示例代码：

private bool isNavigationConfirmed = false;
protected async override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
    base.OnNavigatingFrom(e);
    if (isNavigationConfirmed)
    {
        isNavigationConfirmed = false;
        return;
    }
    e.Cancel = true;

    var noCommand = new UICommand("No", cmd => { });
    var yesCommand = new UICommand("Yes", cmd =>
    {
        if (e.NavigationMode == NavigationMode.Back)
        {
            Frame.GoBack();
        }
        else
        {
            isNavigationConfirmed = true;
            Frame.Navigate(e.SourcePageType);
        }
    });

    var dialog = new MessageDialog("Do you want to allow navigation?");
    dialog.Options = MessageDialogOptions.None;
    dialog.Commands.Add(yesCommand);
    dialog.Commands.Add(noCommand);
    await dialog.ShowAsync();
}

要自己处理导航，请设置Cancel=true（正如您已经做的那样），然后打开对话框以获取用户输入。一旦知道用户的选择，如果用户决定允许进行导航，请使用导航API（例如Frame.GoBack）执行所需的导航（基于例如NavigationMode）

以下是一些基本示例代码：

private bool isNavigationConfirmed = false;
protected async override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
    base.OnNavigatingFrom(e);
    if (isNavigationConfirmed)
    {
        isNavigationConfirmed = false;
        return;
    }
    e.Cancel = true;

    var noCommand = new UICommand("No", cmd => { });
    var yesCommand = new UICommand("Yes", cmd =>
    {
        if (e.NavigationMode == NavigationMode.Back)
        {
            Frame.GoBack();
        }
        else
        {
            isNavigationConfirmed = true;
            Frame.Navigate(e.SourcePageType);
        }
    });

    var dialog = new MessageDialog("Do you want to allow navigation?");
    dialog.Options = MessageDialogOptions.None;
    dialog.Commands.Add(yesCommand);
    dialog.Commands.Add(noCommand);
    await dialog.ShowAsync();
}