[英]VB Assignment of member field programmatically
这个问题是对VB ReDim编程领域的后续。 在对数组进行适当的尺寸调整之后,我尝试设置元素的值,但是当我尝试分配第一个值时,在运行时出现异常(MySB.AssignValues(0,“ B”,0,7.6))
System.InvalidCastException was unhandled
HResult=-2147467262
Message=Object cannot be stored in an array of this type.
Source=mscorlib
Module TestSetArray
Public Class BS
Public A As String
Public B() As Double
Public C() As Double
End Class
Public Class SB
Public MyBS() As BS
'ReadFieldString is a function that returns a string of the field name of Class BS,
'i.e., A, B or C. For test purpose, retun a constant
Public Function ReadFieldString() As String
Return "B"
End Function
'GetArrayDim is a function that returns an integer, which is the size of the array
'of that field name. For test purpose, retun a constant
Public Function GetArrayDim() As Integer
Return 2
End Function
Public Sub DimArrays()
ReDim MyBS(3)
Dim i As Integer
For i = 0 To MyBS.Length - 1
MyBS(i) = New BS()
Dim f = GetType(BS).GetField(ReadFieldString())
f.SetValue(MyBS(i), Array.CreateInstance(f.FieldType.GetElementType(), GetArrayDim()))
Next
End Sub
Public Sub AssignValues(MainIndex As Integer, TheName As String, TheIndex As Integer, TheValue As Double)
Dim f = MyBS(MainIndex).GetType.GetMember(TheName)
f.SetValue(TheValue, TheIndex)
End Sub
End Class
Sub Main()
Dim MySB As SB = New SB
MySB.DimArrays()
MySB.AssignValues(0, "B", 0, 7.6)
MySB.AssignValues(0, "B", 1, 8.2)
End Sub
End Module
提前致谢。
问题在于GetMember方法返回的是MemberInfo类型的数组,而不是类的double数组。 如果您改用GetField,则可能会更轻松。 您必须调用GetValue并将其结果转换为Array才能使用SetValue设置值。
Public Sub AssignValues(MainIndex As Integer, TheName As String, TheIndex As Integer, TheValue As Double)
Dim f = MyBS(MainIndex).GetType().GetField(TheName)
Dim doubleArray = DirectCast(f.GetValue(MyBS(MainIndex)), Array)
doubleArray.SetValue(TheValue, TheIndex)
End Sub
或者,如果您知道该数组将始终是Double的数组,则可以将其直接转换为:
Public Sub AssignValues(MainIndex As Integer, TheName As String, TheIndex As Integer, TheValue As Double)
Dim f = MyBS(MainIndex).GetType().GetField(TheName)
Dim doubleArray = DirectCast(f.GetValue(MyBS(MainIndex)), Double())
doubleArray(TheIndex) = TheValue
End Sub
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