前言

我们都知道.NET Core提供了对依赖项注入的内置支持。我们通常在ASP.NET Core中使用它（从Startup.cs文件中的ConfigureServices方法开始），但是该功能不限于此框架，我们可以在WPF和Windows Forms应用程序中使用它。

实践

1. 新建项目

   

2. 将所需的NuGet包添加到项目中。

   Microsoft.Extensions.DependencyInjection
   • Microsoft.Extensions.Options.ConfigurationExtensions
   • Microsoft.Extensions.Configuration.Json
     

3. 然后，将一个名为appsettings.json的文件添加到项目的根文件夹。将其“ 构建操作”属性设置为“ 内容”，将“复制到输出目录”设置为“ 复制”（如果较新）：

   {
   "AppSettings": {
   "AppName": "SampleNetCore3WpfDependencyInjection"
   }
   }

4. 创建一个AppSettings.cs文件来保存配置设置。该文件将映射我们在appsettings.json中编写的设置：

   public class AppSettings
   {
   public string AppName { get; set; }
   }

5. 创建一个示例服务：

   public interface ISampleService
   {
   Task<string> GetCurrentDate();
   }

   public class SampleService : ISampleService
   {
   public async Task<string> GetCurrentDate() =>
   await Task.FromResult(DateTime.Now.ToLongDateString());
   }

   然后像往常一样在IOC容器中注册服务：

   services.AddScoped<ISampleService, SampleService>();

6. 打开App.xaml文件并删除Application类的StartupUri属性。然后，我们需要重写App.xaml.cs中的OnStartup方法：

   public partial class App : Application
   {
   public IServiceProvider ServiceProvider { get; private set; }
   public IConfiguration Configuration { get; private set; }
   
   protected override void OnStartup(StartupEventArgs e)
   {
   var builder = new ConfigurationBuilder()
   .SetBasePath(Directory.GetCurrentDirectory())
   .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);
   
   Configuration = builder.Build();
   
   var serviceCollection = new ServiceCollection();
   ConfigureServices(serviceCollection);
   
   ServiceProvider = serviceCollection.BuildServiceProvider();
   
   var mainWindow = ServiceProvider.GetRequiredService<MainWindow>();
   mainWindow.Show();
   }
   
   private void ConfigureServices(IServiceCollection services)
   {
   services.Configure<AppSettings>(Configuration.GetSection(nameof(AppSettings)));
   services.AddScoped<ISampleService,
   15d8
   SampleService>();
   services.AddTransient(typeof(MainWindow));
   }
   }

7. MainWindow简单布局及代码改造

   如上所述，MainWindow位于IOC容器中。因此，当我们从服务提供商处获得服务时，它将自动注入所有必需的服务（如果有）。：

   public partial class MainWindow : Window
   {
   private readonly ISampleService sampleService;
   private readonly AppSettings settings;
   
   public MainWindow(ISampleService sampleService,
   IOptions<AppSettings> settings)
   {
   InitializeComponent();
   
   this.sampleService = sampleService;
   this.settings = settings.Value;
   }
   
   private async void Button_Click(object sender, RoutedEventArgs e)
   {
   var serviceData =await sampleService.GetCurrentDate();
   var settingsData = settings;
   TextBox1.Text = $"serviceData:{serviceData}{Environment.NewLine}settingsData:{settings.AppName}";
   }
   }

   

8. Demo地址：github