c# - WinRT 异步调用 Flyout.ShowAt()

Question

我正在构建自己的 Flyout控制列表选择以在 Windows Phone 和 Windows 桌面上使用它。不像ListPickerFlyout类，Flyout类没有显示弹出窗口的异步方法。

如何调用 ShowAt方法异步并在弹出窗口关闭后返回所选值？

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解决方法:

异步行为可以通过 TaskCompletionSource<T> 实现(感谢 AwaitableUI libary )。仍然困扰我的是我必须在构造函数中手动创建 ListView。如果我可以改用 XAML 并只分配一个模板，那就太好了，但我没有找到可行的方法。

public class ListPickerFlyout<T> : Flyout where T : class
{
    private event EventHandler<object> ItemPicked;

    public ListPickerFlyout(IEnumerable<T> items)
    {
        Placement = FlyoutPlacementMode.Full;
        Opening += OnOpening;
        Closed += OnClosed;

        var listView = new ListView();
        listView.SelectionMode = ListViewSelectionMode.None;
        listView.IsItemClickEnabled = true;
        listView.ItemClick += OnItemClick;
        listView.DisplayMemberPath = "Name";
        listView.SetBinding(ListView.ItemsSourceProperty, new Binding { Source = items });

        Content = listView;
    }

    public async Task<T> ShowAsync()
    {
        this.ShowAt(Window.Current.Content as Frame);

        var tcs = new TaskCompletionSource<T>();

        EventHandler<object> eventHandler = null;

        eventHandler = (s, e) =>
        {
            this.Closed -= eventHandler;
            this.ItemPicked -= eventHandler;

            tcs.SetResult(e as T);
        };

        this.Closed += eventHandler;
        this.ItemPicked += eventHandler;

        return await tcs.Task;
    }

    private void OnItemClick(object sender, ItemClickEventArgs e)
    {
        var selectedItem = e.ClickedItem as T;

        var eventHandler = ItemPicked;
        if (eventHandler != null)
            eventHandler(this, selectedItem);

        this.Hide();
    }

    private void OnOpening(object sender, object e)
    {
        var frame = Window.Current.Content as Frame;
        var page = frame.Content as Page;

        if (page != null)
            page.BottomAppBar.Visibility = Visibility.Collapsed;
    }

    private void OnClosed(object sender, object e)
    {
        var frame = Window.Current.Content as Frame;
        var page = frame.Content as Page;

        if (page != null)
            page.BottomAppBar.Visibility = Visibility.Visible;
    }
}

Answer 1

WinRT XAML 工具包具有可等待 UI 的概念，这使得等待许多通常不应用可等待逻辑的 UI 元素成为可能。我还没有在 Flyout 上尝试过，但它可能会起作用。

你可以找到它here