Xamarin Forms 依赖注入与 Microsoft.Extensions.DependencyInjection

Question

我正在尝试使用标准 Microsoft.Extensions.DependencyInjection NuGet package 设置基本 DI。

目前我正在注册我的依赖项，如下所示：

public App()
{
    InitializeComponent();
    var serviceCollection = new ServiceCollection();
    ConfigureServices(serviceCollection);
}

private static void ConfigureServices(ServiceCollection serviceCollection)
{
    serviceCollection.AddSingleton<IRestClient>(_ => new RestClient("https://localhost:44379/api/"));
    serviceCollection.AddScoped<ICommHubClient, CommHubClient>();
}

我使用需要像这样的依赖项的视图模型：

 public ChatListViewModel(
        ICommHubClient client,
        IRestClient restClient
        )

在页面的代码隐藏文件（.xaml.cs）中，我需要提供 viewModel，但我也需要在那里提供依赖项。

public ChatListPage()
{
     InitializeComponent();
     BindingContext = _viewModel = new ChatListViewModel(); //CURRENTLY THROWS ERROR BECAUSE NO DEPENDENCIES ARE PASSED!
}

有谁知道我如何在 Xamarin Forms 中使用 Microsoft.Extensions.DependencyInjection 应用依赖注入（注册和解析）？

Answer 1

您还应该在 DI Container 中注册您的 ViewModel，而不仅仅是您的服务：

在App.xaml.cs您的代码更改为：

public ServiceProvider ServiceProvider { get; }

public App()
{
    InitializeComponent();
    
    var serviceCollection = new ServiceCollection();
    ConfigureServices(serviceCollection);
    ServiceProvider = serviceCollection.BuildServiceProvider();
    
    MainPage = new ChatListPage();
}

private void ConfigureServices(ServiceCollection serviceCollection)
{
    serviceCollection.AddSingleton<IRestClient>(_ => new RestClient("https://localhost:44379/api/"));
    serviceCollection.AddScoped<ICommHubClient, CommHubClient>();
    serviceCollection.AddTransient<ChatListViewModel>();
}

然后您可以从ServiceProvider解析您的 ViewModel

public ChatListPage()
{
    InitializeComponent();
    BindingContext = _viewModel = ((App)Application.Current).ServiceProvider.GetService(typeof(ChatListViewModel)) as ChatListViewModel;
}