VB.NET:通过反射实例化嵌套的属性

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问题描述

我想通过反射来设置属性的值.在此线程中，提出解决方案.但是解决方案的问题在于它没有实例化属性.但是如果需要，我想检查并实例化属性.我的DTO是:

I want to set the values of the properties via reflection. In this thread they propose a solution. But the problem with the solution is that it is not instantiating the properties. But I want to check and instantiate the properties if necessary. My DTO is:

Public Class root
    Public Property Printing() As rootPrinting
End Class

Public Class rootPrinting
    Public Property Printer() As String
    Public Property PrinterBatch() As String
End Class

现在用于设置属性的我已经定义了以下功能:

Now for setting the properties I have defined the following function:

Public Sub SetProperty(ByVal target As Object, ByVal compoundProperty As String, ByVal value As Object)
    Dim properties As String() = compoundProperty.Split("."c)
    For i As Integer = 0 To properties.Length - 1 - 1
        Dim propertyToGet As PropertyInfo = target.[GetType]().GetProperty(properties(i))
        target = propertyToGet.GetValue(target, Nothing)
        if IsNothing(target) then
            if propertyToGet.PropertyType.IsClass then
                target = Activator.CreateInstance(propertyToGet.PropertyType)
            End If
        End If
    Next

    Dim propertyToSet As PropertyInfo = target.[GetType]().GetProperty(properties.Last())
    propertyToSet.SetValue(target, value, Nothing)
End Sub

然后我这样称呼它:

Dim configObject as New root
SetProperty(configObject , "Printing.Printer","skjfkd")

如果在调用SetProperty(configObject,...)之前我实例化了configObject.Printing，那么它将正常工作:

If before calling SetProperty(configObject,...) I instantiate configObject.Printing then it will work fine:

Dim configObject as New root
configObject.Printing = new rootPrinting()
SetProperty(configObject , "Printing.Printer","skjfkd")

否则，调用SetProperty(...)后，configObject.Printing将为Nothing.
似乎在调用Activator.CreateInstance(propertyToGet.PropertyType)时，对原始对象的引用会丢失.当函数中的对象真正被初始化时，主对象仍为Nothing.如何正确实例化class属性?

Otherwise after calling SetProperty(...), configObject.Printing will be Nothing.
It seems that when calling Activator.CreateInstance(propertyToGet.PropertyType) the reference to the original object is lost. While the object in the function is really initialized, the main object remains Nothing. How can I instantiate the class property correctly?

推荐答案

好.问题解决了.为了解决该问题，必须对代码进行如下修改:

Ok. The problem was solved. To solve the problem the code has to be modified as following:

Public Sub SetProperty(ByVal target As Object, ByVal compoundProperty As String, ByVal value As Object)

   Dim properties As String() = compoundProperty.Split("."c)

   For i As Integer = 0 To properties.Length - 1 - 1
      Dim propertyToGet As PropertyInfo = target.GetType().GetProperty(properties(i))
      Dim property_value = propertyToGet.GetValue(target, Nothing)
      If IsNothing(property_value) Then
         If propertyToGet.PropertyType.IsClass Then
            property_value = Activator.CreateInstance(propertyToGet.PropertyType)
            propertyToGet.SetValue(target, property_value)
         End If
      End If
      target = property_value
   Next

   Dim propertyToSet As PropertyInfo = target.GetType().GetProperty(properties.Last())
   propertyToSet.SetValue(target, value)

End Sub

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printing