少有人走的路

sender as ObservableCollection<string> 为啥为null ? 

查看下sender的传入值，确实是有内容的。

查看下sender的定义如下，确实是一个ObservableCollection<string>类型。

用即时窗口看下：

sender is List<string>
false
sender is ObservableCollection<string>
false
sender as List<string>
null

为啥子显示不是一个ObservableCollection<string>类型呢？

没办法，看下系统反射判断的这个sender定义的类型到底是啥：

sender.GetType()
{Name = "ObservableCollection`1" FullName = "System.Collections.ObjectModel.ObservableCollection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"}
    Assembly: {System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089}
    AssemblyQualifiedName: "System.Collections.ObjectModel.ObservableCollection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]], System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Attributes: Public | Serializable | BeforeFieldInit
    BaseType: {Name = "Collection`1" FullName = "System.Collections.ObjectModel.Collection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"}
    ContainsGenericParameters: false
    CustomAttributes: Count = 3
    DeclaredConstructors: {System.Reflection.ConstructorInfo[3]}
    DeclaredEvents: {System.Reflection.EventInfo[3]}
    DeclaredFields: {System.Reflection.FieldInfo[5]}
    DeclaredMembers: {System.Reflection.MemberInfo[34]}
    DeclaredMethods: {System.Reflection.MethodInfo[22]}
    DeclaredNestedTypes: {System.Reflection.TypeInfo.<get_DeclaredNestedTypes>d__23}
    DeclaredProperties: {System.Reflection.PropertyInfo[0]}
    DeclaringMethod: '((System.RuntimeType)(sender.GetType())).DeclaringMethod' threw an exception of type 'System.InvalidOperationException'
    DeclaringType: null
    FullName: "System.Collections.ObjectModel.ObservableCollection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"
    GUID: {eed6258a-e0b5-3222-9bfe-53563367be16}
    GenericParameterAttributes: '((System.RuntimeType)(sender.GetType())).GenericParameterAttributes' threw an exception of type 'System.InvalidOperationException'
    GenericParameterPosition: '((System.RuntimeType)(sender.GetType())).GenericParameterPosition' threw an exception of type 'System.InvalidOperationException'
    GenericTypeArguments: {System.Type[1]}
    GenericTypeParameters: {System.Type[0]}
    HasElementType: false
    ImplementedInterfaces: {System.Type[10]}
    IsAbstract: false
    IsAnsiClass: true
    IsArray: false
    IsAutoClass: false
    IsAutoLayout: true
    IsByRef: false
    IsCOMObject: false
    IsClass: true
    IsConstructedGenericType: true
    IsContextful: false
    IsEnum: false
    IsExplicitLayout: false
    IsGenericParameter: false
    IsGenericType: true
    IsGenericTypeDefinition: false
    IsImport: false
    IsInterface: false
    IsLayoutSequential: false
    IsMarshalByRef: false
    IsNested: false
    IsNestedAssembly: false
    IsNestedFamANDAssem: false
    IsNestedFamORAssem: false
    IsNestedFamily: false
    IsNestedPrivate: false
    IsNestedPublic: false
    IsNotPublic: false
    IsPointer: false
    IsPrimitive: false
    IsPublic: true
    IsSealed: false
    IsSecurityCritical: false
    IsSecuritySafeCritical: false
    IsSecurityTransparent: true
    IsSerializable: true
    IsSpecialName: false
    IsUnicodeClass: false
    IsValueType: false
    IsVisible: true
    MemberType: TypeInfo
    MetadataToken: 33555385
    Module (System.Reflection.MemberInfo): {System.dll}
    Module: {System.dll}
    Name: "ObservableCollection`1"
    Namespace: "System.Collections.ObjectModel"
    ReflectedType: null
    StructLayoutAttribute: {System.Runtime.InteropServices.StructLayoutAttribute}
    TypeHandle: {System.RuntimeTypeHandle}
    TypeInitializer: null
    UnderlyingSystemType: {Name = "ObservableCollection`1" FullName = "System.Collections.ObjectModel.ObservableCollection`1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"}

系统判断类型是System.Collections.ObjectModel.ObservableCollection

而鼠标指向 sender as ObservableCollection<string> 这一句，显示ObservableCollection的类型是 UIShell.OSGI.Collection.ObservableCollection！！

想不到吧！ ObservableCollection在其它的类库中可能也有相同的类型。

一直以为系统的类型不可能在其它类型中再定义的。

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