单元测试 MxvAsyncCommand 时 MVVM 交叉空引用

Question

我们最近升级到 MvvMCross 6.2.2 并注意到我们必须更改为使用 Mvx.IoCProvider。

我们发现，如果我们在 ViewModel 中构造 MvxAsyncCommand，这会导致所有调用此构造函数的单元测试出现空引用异常

*

Result StackTrace:  
at MvvmCross.Commands.MvxCommandBase..ctor()
   at MvvmCross.Commands.MvxAsyncCommand..ctor(Func`1 execute, Func`1 canExecute, Boolean allowConcurrentExecutions)
   at App.Mobile.Core.ViewModels.TestViewModel..ctor(IMvxNavigationService navigation, ITestService encService, ILogger logger)
   at App.Mobile.Core.UnitTests.TestViewModelTests.<TestViewModel_Prepare>d__1.MoveNext()

*

查看 github 中的源，问题是由于 Mvx.IocProvider 为空。

public MvxCommandBase()
    {
        if (!Mvx.IoCProvider.TryResolve<IMvxCommandHelper>(out _commandHelper))
            _commandHelper = new MvxWeakCommandHelper();

        var alwaysOnUIThread = MvxSingletonCache.Instance == null || MvxSingletonCache.Instance.Settings.AlwaysRaiseInpcOnUserInterfaceThread;
        ShouldAlwaysRaiseCECOnUserInterfaceThread = alwaysOnUIThread;
    }

已在“开发”分支中实施了修复，但这在 nuget 上不可用。

public MvxCommandBase()
    {
        // fallback on MvxWeakCommandHelper if no IoC has been set up
        if (!Mvx.IoCProvider?.TryResolve(out _commandHelper) ?? true)
            _commandHelper = new MvxWeakCommandHelper();

        // default to true if no Singleton Cache has been set up
        var alwaysOnUIThread = MvxSingletonCache.Instance?.Settings.AlwaysRaiseInpcOnUserInterfaceThread ?? true;
        ShouldAlwaysRaiseCECOnUserInterfaceThread = alwaysOnUIThread;
    }

有谁知道在我们的单元测试项目中初始化这个 IoCProvider 的解决方法。

Answer 1

As you can see here the IoCProvider is resolved by getting the singleton of IMvxIoCProvider

public static IMvxIoCProvider IoCProvider => MvxSingleton<IMvxIoCProvider>.Instance;

So all you have to do is to initialize the IMvxIoCProvider. As an example you can use this test, so in order to initialize it, you have to do:

MvxSingleton.ClearAllSingletons(); // This should be done in the test to clear all references of previous tests if necessary.
var instance = MvxIoCProvider.Initialize();

HIH