WPF/C#：实现导航功能

前言

在WPF中使用导航功能可以使用Frame控件，这是比较基础的一种方法。前几天分享了wpfui中NavigationView的基本用法，但是如果真正在项目中使用起来，基础的用法是无法满足的。今天通过wpfui中的mvvm例子来说明在wpfui中如何通过依赖注入与MVVM模式使用导航功能。实践起来，我个人觉得这个例子中实现导航功能还是有点麻烦的，但我也不知道怎么能更优雅，也是学到了一些东西吧。

wpfui中MVVM例子的地址在：https://github.com/lepoco/wpfui/tree/main/src/Wpf.Ui.Demo.Mvvm

实现效果如下所示：

如果你对此感兴趣，可以继续阅读。

实践

使用依赖注入

将主窗体与主窗体的ViewModel与每个页面与每个页面的ViewModel都存入依赖注入容器中：

当然不只是窗体页面与ViewModel，也需要注册一些服务。

为了实现导航功能，使用了两个服务分别是NavigationService与PageService。

NavigationService在wpfui库中已经自带了，直接使用即可：

具体代码可自行研究，这里就不放了。

而PageService在wpfui中没有自带，需要自己定义，MVVM例子中的定义如下所示：

 public class PageService : IPageService{/// <summary>/// Service which provides the instances of pages./// </summary>private readonly IServiceProvider _serviceProvider;/// <summary>/// Initializes a new instance of the <see cref="PageService"/> class and attaches the <see cref="IServiceProvider"/>./// </summary>public PageService(IServiceProvider serviceProvider){_serviceProvider = serviceProvider;}/// <inheritdoc />public T? GetPage<T>()where T : class{if (!typeof(FrameworkElement).IsAssignableFrom(typeof(T))){throw new InvalidOperationException("The page should be a WPF control.");}return (T?)_serviceProvider.GetService(typeof(T));}/// <inheritdoc />public FrameworkElement? GetPage(Type pageType){if (!typeof(FrameworkElement).IsAssignableFrom(pageType)){throw new InvalidOperationException("The page should be a WPF control.");}return _serviceProvider.GetService(pageType) as FrameworkElement;}}

现在已经将所有窗体、页面、ViewModels与相关服务都注册到容器中了。

ViewModel

在MainWindowViewModel中将页面存入一个属性中：

在非首页的ViewModel中实现INavigationAware接口：

View

MainWindow.cs如下所示：

 public partial class MainWindow : INavigationWindow{public ViewModels.MainWindowViewModel ViewModel { get; }public MainWindow(ViewModels.MainWindowViewModel viewModel,IPageService pageService,INavigationService navigationService){ViewModel = viewModel;DataContext = this;Wpf.Ui.Appearance.SystemThemeWatcher.Watch(this);InitializeComponent();SetPageService(pageService);navigationService.SetNavigationControl(RootNavigation);}public INavigationView GetNavigation() => RootNavigation;public bool Navigate(Type pageType) => RootNavigation.Navigate(pageType);public void SetPageService(IPageService pageService) => RootNavigation.SetPageService(pageService);public void ShowWindow() => Show();public void CloseWindow() => Close();/// <summary>/// Raises the closed event./// </summary>protected override void OnClosed(EventArgs e){base.OnClosed(e);// Make sure that closing this window will begin the process of closing the application.Application.Current.Shutdown();}INavigationView INavigationWindow.GetNavigation(){throw new NotImplementedException();}public void SetServiceProvider(IServiceProvider serviceProvider){throw new NotImplementedException();}}

首先实现了INavigationWindow接口。在构造函数中注入所需的依赖类。注意这里的RootNavigation其实就是页面中NavigationView的名称：

刚开始看这里没注意到，卡壳了很久。

因为你在代码中查看定义，它会转到这个地方：

没经验不知道是什么，但是这次过后，知道这是在Xaml中定义，由工具自动生成的代码了。

其他的页面改成了这样的写法：

 public partial class DashboardPage : INavigableView<DashboardViewModel>{public DashboardViewModel ViewModel { get; }public DashboardPage(DashboardViewModel  viewModel){ViewModel = viewModel;this.DataContext = this;InitializeComponent();          }}

都实现了INavigableView<out T>接口：

显示主窗体与主页面

现在准备工作都做好了，下一步就是显示主窗体与主页面了。

在容器中我们也注入了这个：

ApplicationHostService如下所示：

    /// <summary>/// Managed host of the application./// </summary>public class ApplicationHostService : IHostedService{private readonly IServiceProvider _serviceProvider;private INavigationWindow? _navigationWindow;public ApplicationHostService(IServiceProvider serviceProvider){_serviceProvider = serviceProvider;}/// <summary>/// Triggered when the application host is ready to start the service./// </summary>/// <param name="cancellationToken">Indicates that the start process has been aborted.</param>public async Task StartAsync(CancellationToken cancellationToken){await HandleActivationAsync();}/// <summary>/// Triggered when the application host is performing a graceful shutdown./// </summary>/// <param name="cancellationToken">Indicates that the shutdown process should no longer be graceful.</param>public async Task StopAsync(CancellationToken cancellationToken){await Task.CompletedTask;}/// <summary>/// Creates main window during activation./// </summary>private async Task HandleActivationAsync(){await Task.CompletedTask;if (!System.Windows.Application.Current.Windows.OfType<MainWindow>().Any()){_navigationWindow = (_serviceProvider.GetService(typeof(INavigationWindow)) as INavigationWindow)!;_navigationWindow!.ShowWindow();_ = _navigationWindow.Navigate(typeof(DashboardPage));}await Task.CompletedTask;}}
}

在app.xaml中定义了程序启动与退出事件的处理程序：

 /// <summary>/// Occurs when the application is loading./// </summary>private async void OnStartup(object sender, StartupEventArgs e){await _host.StartAsync();}/// <summary>/// Occurs when the application is closing./// </summary>private async void OnExit(object sender, ExitEventArgs e){await _host.StopAsync();_host.Dispose();}