C# WinUI 3 Desktop 如何向应用程序实例公开接口？

Question

尝试使用我发现的此解决方案通过代码隐藏来实现 NavigationView 导航：https://xamlbrewer.wordpress.com/2021/07/06/navigating-in-a-winui-3-desktop-application/

我收到此编译错误：

错误是说我应该“投射”m_window；该示例未投射。为什么我需要投射？

我创建了一个界面：(INavigation.cs)

using Microsoft.UI.Xaml.Controls;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MetricReporting.Interfaces
{
    interface INavigation
    {
        NavigationViewItem GetCurrentNavigationViewItem();

        List<NavigationViewItem> GetNavigationViewItems();

        List<NavigationViewItem> GetNavigationViewItems(Type type);

        List<NavigationViewItem> GetNavigationViewItems(Type type, string title);

        void SetCurrentNavigationViewItem(NavigationViewItem item);
    }
}

我创建了主窗口的部分类（MainWindow.xaml.Navigation.cs）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MetricReporting
{
    public partial class MainWindow : INavigation
    {
        public NavigationViewItem GetCurrentNavigationViewItem()
        {
            return NavigationView.SelectedItem as NavigationViewItem;
        }

        public List<NavigationViewItem> GetNavigationViewItems()
        {
            var result = new List<NavigationViewItem>();
            var items = NavigationView.MenuItems.Select(i => (NavigationViewItem)i).ToList();
            items.AddRange(NavigationView.FooterMenuItems.Select(i => (NavigationViewItem)i));
            result.AddRange(items);
 
            foreach (NavigationViewItem mainItem in items)
            {
                result.AddRange(mainItem.MenuItems.Select(i => (NavigationViewItem)i));
            }
 
            return result;
        }
 
        public List<NavigationViewItem> GetNavigationViewItems(Type type)
        {
            return GetNavigationViewItems().Where(i => i.Tag.ToString() == type.FullName).ToList();
        }
 
        public List<NavigationViewItem> GetNavigationViewItems(Type type, string title)
        {
            return GetNavigationViewItems(type).Where(ni => ni.Content.ToString() == title).ToList();
        }

        public void SetCurrentNavigationViewItem(NavigationViewItem item)
        {
            if (item == null)
            {
                return;
            }

            if (item.Tag == null)
            {
                return;
            }

            MasterContentFrame.Navigate(
            Type.GetType(item.Tag.ToString()),
            item.Content);
            NavigationView.Header = item.Content;
            NavigationView.SelectedItem = item;
        }
    }
}

我将此行添加到我的 App.xaml.cs 文件中：

public INavigation Navigation => m_window;

它模拟了文章中的线条：

private Shell shell;
 
public INavigation Navigation => shell;
         
protected override void OnLaunched(LaunchActivatedEventArgs args)
{
    shell = new Shell();
    shell.Activate();
}

我应该能够像这样使用导航服务：

All parts of the code base can now easily access the lightweight Navigation Service:

(Application.Current as App).Navigation

为了清楚起见，这是我的 App.xaml.cs

using MetricReporting.Interfaces;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Navigation;
    
namespace MetricReporting
{
    public partial class App : Application
    {
        /// <summary>
        /// Initializes the singleton application object.  This is the first line of authored code
        /// executed, and as such is the logical equivalent of main() or WinMain().
        /// </summary>
        public App()
        {
            this.InitializeComponent();
        }

        /// <summary>
        /// Invoked when the application is launched normally by the end user.  Other entry points
        /// will be used such as when the application is launched to open a specific file.
        /// </summary>
        /// <param name="args">Details about the launch request and process.</param>
        /// 

        protected override void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
        {
            m_window = new MainWindow();
            m_window.Activate();
        }

        private Window m_window;

        public INavigation Navigation => m_window;   //Compiler does not like this
        //public INavigation Navigation => m_window;   Compiler does not like this
    }
}

Answer 1

m_window

是一个

Window

...所以它可能是 any

Window

而不一定是你的

MainWindow

，或者任何实现

INavigation

的东西。这就是构建的所有信息。

你可以用以下方法修复它：

private MainWindow m_window;

Answer 2

您需要将

m_window

转换为

INavigation

才能编译代码：

public INavigation Navigation => m_window as INavigation;

或者按照 @rfmodulator (+1) 的建议直接将

m_window

字段定义为

INavigation

：

private MainWindow m_window;

Answer 3

我运行了相同的代码，错误是隐式继承了错误的接口。

在下面的行中，接口

INavigation

来自命名空间：

namespace Microsoft.EntityFrameworkCore.Metadata

。

public INavigation Navigation => m_window;

只需直接指定您正在使用哪个接口，例如，如果您想使用您的实现：

public MetricReporting.Services.Interfaces.INavigation Navigation => m_window;

或更改您的界面名称，例如

IMainWindowsNavigation

。