DotNet MAUI 7中IDispatcherTimer注入致单元测试编译失败

我在MAUI 7应用中使用Microsoft依赖注入，此前构造注入和单元测试都正常。但注入IDispatcherTimer相关接口后，应用可以正常运行，单元测试却编译失败，错误提示需要引用Microsoft.Maui程序集。我认为单元测试项目不应该依赖.NET MAUI。

单元测试编译错误信息 #

Severity    Code    Description Project File    Line    Suppression State
Error   CS0012  The type 'IDispatcherTimer' is defined in an assembly that is not referenced. You must add a reference to assembly 'Microsoft.Maui, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. MineSweeperTests    C:\Users\markwardell\source\repos\MineSweeper\MineSweeperTests\ViewModels\SweeperViewModel-Tests.cs 28  Active

相关代码 #

被测ViewModel构造函数 #

public SweeperViewModel(ILogger<SweeperViewModel> logger, IGameBoardViewModel gameBoard, IDispatcherTimer dispatchTimer)
{
   _logger = logger;
   _gameBoard = gameBoard;
   _timer = dispatchTimer;   
}

GameTimer实现类 #

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

namespace MineSweeper.Models
{
   public class GameTimer : IGameTimer
   {
      IDispatcherTimer _timer;
      public GameTimer()
      {
         _timer = Application.Current.Dispatcher.CreateTimer();
      }
      public TimeSpan Interval {  get => _timer.Interval; set => _timer.Interval = value; }
      public bool IsRepeating {  get => _timer.IsRepeating; set => _timer.IsRepeating = value; }

      public bool IsRunning => _timer.IsRunning;

      public event EventHandler Tick;

      public void Start()
      {
         _timer.Start();
      }

      public void Stop()
      {
         _timer.Stop();      
      }
   }
}

IGameTimer接口（与Microsoft.Maui.Dispatching.IDispatcherTimer完全一致但独立） #

namespace MineSweeper.Models
{
   public interface IGameTimer
   {
      public TimeSpan Interval { get; set; }
      public bool IsRepeating { get; set; }

      public bool IsRunning { get; }

      public event EventHandler Tick;

      public void Start();

      public void Stop();
   }
}

问题核心是ViewModel构造函数直接依赖了MAUI的IDispatcherTimer接口，这个类型属于Microsoft.Maui程序集，而单元测试项目没有引用该程序集，导致编译报错。你已经定义了独立的IGameTimer接口，完全可以用它来解耦ViewModel与MAUI的依赖。

具体修改步骤：

1. 修改ViewModel构造函数，将参数类型从IDispatcherTimer替换为自定义的IGameTimer：

public SweeperViewModel(ILogger<SweeperViewModel> logger, IGameBoardViewModel gameBoard, IGameTimer gameTimer)
{
   _logger = logger;
   _gameBoard = gameBoard;
   _timer = gameTimer;   
}

2. 在MAUI应用的DI容器中注册依赖：

builder.Services.AddSingleton<IGameTimer, GameTimer>();

3. 单元测试时使用Mock实现：
   用Moq等框架创建IGameTimer的Mock实例，完全不需要依赖MAUI程序集，示例如下：

var mockTimer = new Mock<IGameTimer>();
// 根据测试需求设置Mock行为，比如模拟Tick触发、验证Start/Stop调用等
var viewModel = new SweeperViewModel(mockLogger.Object, mockGameBoard.Object, mockTimer.Object);

修改后，ViewModel不再直接依赖MAUI特定类型，单元测试项目无需引用Microsoft.Maui，同时应用端的功能不受影响。

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