C# 警报框不在xamarin表单中显示，DisplayAlert（）

我试图在点击或单击所选的ListView框后显示提醒框。当前selectedItem正在绑定到SelectedTicket，这将触发ViewModel中的对象调用SelectedTicket。触发SelectedTicket后，它将使用DisplayAlert方法执行popup.show方法。执行DisplayAlert方法get，但不显示AlertBox

==============================================

////Xaml页面

<ListView ItemsSource="{Binding TicketList,Mode=OneWay}" RowHeight="130"
     ItemTemplate="{StaticResource TicketListTileTemplate}"  BackgroundColor="#d9deeb"
     SelectedItem="{Binding SelectedTicket, Mode=TwoWay}" SeparatorVisibility="None">
</ListView>

======================================================

////弹出窗口.cs

async public void Show()
{
    DisplayAlert("Alert", "Your have been alerted", "OK");
}

DisplayAlert仅对ContentPage或NavigationPage等页面对象可用。请参见，您的Popup.cs可能不是页面对象。此外，您也没有等待DisplayAlert，这是您一直希望使用异步方法执行的操作。最后，您的Show方法可能没有在UI线程上运行

与其尝试从ViewModel中显示警报，不如尝试从XAML页面的代码隐藏中显示警报，如下所示：

XAML：

---

我看不到DisplayAlert的一个最常见的原因是，它是在屏幕上不活动的页面上被调用的

作为快速解决方法/测试，您可以

await Application.Current.MainPage.DisplayAlert("Alert", "Your have been alerted", "OK");

如果这是可行的，我的第一个假设就得到了证实

我总是试图保持代码的整洁，因此从ViewModel调用当然是一个好方法。通常，MVVM库有一些代码来帮助显示警报

<ListView ItemsSource="{Binding TicketList,Mode=OneWay}" 
          RowHeight="130"
          ItemTemplate="{StaticResource TicketListTileTemplate}" BackgroundColor="#d9deeb"
          SelectedItem="{Binding SelectedTicket, Mode=TwoWay}"
          SeparatorVisibility="None"
          ItemSelected="OnItemTapped"> <!-- Notice ItemTapped here will trigger when an item is tapped, imagine that -->

....

private TicketViewModel _viewModel = new TicketViewModel();

....

public async void OnItemTapped (object o, ItemTappedEventArgs e) { //Notice I added 'async' to the method here, that is so we can 'await' the DisplayAlert below (ALWAYS 'await' the DisplayAlert and ANY other async methods)
    TicketListItem item = (TicketListItem)o;

    if (item != null) {
        await DisplayAlert("Alert", "Your have been alerted", "OK"); //Notice the 'await' here
        _viewModel.SelectedTicket = null;
    }
}

await Application.Current.MainPage.DisplayAlert("Alert", "Your have been alerted", "OK");