WinUI3子页面创建FilePicker抛出异常及解决过程

从WinUI3 Gallery复制的文件选择器代码在MainWindow中运行正常，但在子页面执行相同操作时抛出异常。已知问题出在获取窗口句柄（HWND）上，但不知道如何解决。本人刚接触C#和WinUI3，几周前才完成第一个Hello World程序。

按钮点击事件代码 #

private async void PickAFileButton_Click(object sender, RoutedEventArgs e)
{
    // 清除之前返回的文件名（如果存在）
    OutputTextBlock.Text = "";

    // 创建文件选择器
    var openPicker = new Windows.Storage.Pickers.FileOpenPicker();

    // 获取当前WinUI 3窗口的句柄（HWND）
    var window = WindowHelper.GetWindowForElement(this);
    var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(window);

    // 使用窗口句柄初始化文件选择器
    WinRT.Interop.InitializeWithWindow.Initialize(openPicker, hWnd);

    // 设置文件选择器选项
    openPicker.ViewMode = PickerViewMode.Thumbnail;
    openPicker.FileTypeFilter.Add("*");

    // 打开选择器让用户选择文件
    var file = await openPicker.PickSingleFileAsync();
    if (file != null)
    {
        PickAFileOutputTextBlock.Text = "选中文件: " + file.Name;
    }
    else
    {
        PickAFileOutputTextBlock.Text = "操作已取消。";
    }
}

WindowHelper.cs代码 #

//*********************************************************
//
// Copyright (c) Microsoft. All rights reserved.
// THIS CODE IS PROVIDED *AS IS* WITHOUT WARRANTY OF
// ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING ANY
// IMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR
// PURPOSE, MERCHANTABILITY, OR NON-INFRINGEMENT.
//
//*********************************************************

using Microsoft.UI;
using Microsoft.UI.Windowing;
using Microsoft.UI.Xaml;
using System;
using System.Collections.Generic;
using WinRT.Interop;

namespace AppUIBasics.Helper
{
    // 辅助类，用于查找包含任意UIElement的窗口（GetWindowForElement）。
    // 为此，我们需要跟踪所有活动窗口。应用代码必须调用WindowHelper.CreateWindow
    // 而不是直接"new Window"，这样我们才能跟踪所有相关窗口。未来平台API可能会原生支持此功能。
    public class WindowHelper
    {
        static public Window CreateWindow()
        {
            Window newWindow = new Window();
            TrackWindow(newWindow);
            return newWindow;
        }

        static public void TrackWindow(Window window)
        {
            window.Closed += (sender, args) => {
                _activeWindows.Remove(window);
            };
            _activeWindows.Add(window);
        }

        static public AppWindow GetAppWindow(Window window)
        {
            IntPtr hWnd = WindowNative.GetWindowHandle(window);
            WindowId wndId = Win32Interop.GetWindowIdFromWindow(hWnd);
            return AppWindow.GetFromWindowId(wndId);
        }

        static public Window GetWindowForElement(UIElement element)
        {
            if (element.XamlRoot != null)
            {
                foreach (Window window in _activeWindows)
                {
                    if (element.XamlRoot == window.Content.XamlRoot)
                    {
                        return window;
                    }
                }
            }
            return null;
        }

        static public UIElement FindElementByName(UIElement element, string name)
        {
            if (element.XamlRoot != null && element.XamlRoot.Content != null)
            {
                var ele = (element.XamlRoot.Content as FrameworkElement).FindName(name);
                if (ele != null)
                {
                    return ele as UIElement;
                }
            }
            return null;
        }

        static public List<Window> ActiveWindows { get { return _activeWindows; }}

        static private List<Window> _activeWindows = new List<Window>();
    }
}

更新 #

曾出现新错误，最终通过重建项目解决了该问题。

内容的提问来源于stack exchange，提问作者unsealed1051