我现在正在启动一个新的 Silverlight 项目，如果我的 ViewModel（它正在为我实例化）包含 RaisePropertyChanged 事件，我会遇到 Unity 引发异常的问题。
我看起来像这样：
public class AddNewClientViewModel : ViewModelBase {
private Visibility _extraClientFieldsVisible;
public Visibility ExtraClientFieldsVisible {
get {
return _extraClientFieldsVisible;
}
set {
_extraClientFieldsVisible = value;
base.RaisePropertyChanged("ExtraClientFieldsVisible");
}
}
public AddNewClientViewModel(IMyInterface blah) {
ExtraClientFieldsVisible = Visibility.Collapsed;
}
它继承的 ViewModelBase 如下所示：
public abstract class ViewModelBase : INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName) {
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
完整的堆栈跟踪如下所示，但似乎在构造函数期间调用 RaisePropertyChanged 事件会导致 Unity 崩溃。
这是错误的完整堆栈跟踪：
Microsoft.Practices.Unity.ResolutionFailedException was unhandled by user code
Message="Resolution of the dependency failed, type = \"ClientSide.ViewModels.AddNewClientViewModel\", name = \"\". Exception message is: The current build operation (build key Build Key[ClientSide.ViewModels.AddNewClientViewModel, null]) failed: Object reference not set to an instance of an object. (Strategy type BuildPlanStrategy, index 3)"
TypeRequested="AddNewClientViewModel"
StackTrace:
at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name)
at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, String name)
at Microsoft.Practices.Unity.UnityContainer.Resolve(Type t, String name)
at Microsoft.Practices.Unity.UnityContainerBase.Resolve(Type t)
at Microsoft.Practices.Unity.UnityContainerBase.Resolve[T]()
at ClientSide.Framework.ServiceLocator.get_AddNewClientViewModel()
InnerException: Microsoft.Practices.ObjectBuilder2.BuildFailedException
Message="The current build operation (build key Build Key[ClientSide.ViewModels.AddNewClientViewModel, null]) failed: Object reference not set to an instance of an object. (Strategy type BuildPlanStrategy, index 3)"
BuildKey="Build Key[ClientSide.ViewModels.AddNewClientViewModel, null]"
ExecutingStrategyIndex=3
ExecutingStrategyTypeName="BuildPlanStrategy"
StackTrace:
at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
at Microsoft.Practices.ObjectBuilder2.Builder.BuildUp(IReadWriteLocator locator, ILifetimeContainer lifetime, IPolicyList policies, IStrategyChain strategies, Object buildKey, Object existing)
at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name)
InnerException: System.NullReferenceException
Message="Object reference not set to an instance of an object."
StackTrace:
at ClientSide.ViewModels.ViewModelBase.RaisePropertyChanged(String propertyName)
at ClientSide.ViewModels.AddNewClientViewModel.set_ExtraClientFieldsVisible(Visibility value)
at ClientSide.ViewModels.AddNewClientViewModel..ctor(IDataCore dataCore)
at BuildUp_ClientSide.ViewModels.AddNewClientViewModel(IBuilderContext )
at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context)
at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context)
at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context)
InnerException:
所以我遇到了 NullReferenceException。我无法弄清楚如何...