C＃Reflection - 更改变量字段的值

Question

I have an instance of a class, I want to change an object data member of this instance only with another object of the same type (swap), due to my system constraints i can't use =,new or setter operators.

Basically I would like to change the value of a field of a variable, the field is an object contained inside another object - the variable which its instance I have.

is it possible using reflection? if so can someone please give me basic direction?

Thanks Yoav

Answer 1

Yes, its possible.

In short, do something like

Type typeInQuestion = typeof(TypeHidingTheField);
FieldInfo field = typeInQuestion.GetField("FieldName", BindingFlags.NonPublic | BindingFlags.Instance);
field.SetValue(instanceOfObject, newValue);

to change the value of a hidden (private/protected/internal) field. Use the corresponding FieldInfo.GetValue(...) to read; combine the two trivially to get your desired swapping operation.

Don't hold me to the BindingFlags (I always seem to get those wrong on the first attempt) or the exact syntax, but that's basically it.

Look over System.Reflection for reference.

Answer 2

If you use .NET 3.5, you can use my open-source library, Fasterflect , to address that with the following code:

typeof(MyType).SetField("MyField", anotherObject);

When using Fasterflect, you don't have to bother with the right BindingFlags specification and the performance implication (as when using reflection).

Answer 3

in vb with generics, but rudimentary error handling:

Module somereflectionops
    Function GetFieldValue(Of OBTYPE, FIELDTYPE)(instance As OBTYPE, fieldname As String,  Optional specbindingflags As BindingFlags = BindingFlags.NonPublic Or BindingFlags.Instance) As FIELDTYPE
        Dim ot As Type = GetType(OBTYPE)
        Dim fi As FieldInfo
        Try
            fi = ot.GetField(fieldname, BindingFlags.Default Or specbindingflags)
            If fi Is Nothing Then Return Nothing
            Return fi.GetValue(instance)
        Catch ex As Exception
            Return Nothing
        End Try
    End Function

    Function SetFieldValue(Of OBTYPE, FIELDTYPE)(instance As OBTYPE, fieldname As String, value As FIELDTYPE, Optional specbindingflags As BindingFlags = BindingFlags.NonPublic Or BindingFlags.Instance) As Boolean
        Dim ot As Type = GetType(OBTYPE)
        Dim fi As FieldInfo
        Try
            fi = ot.GetField(fieldname,  BindingFlags.Default Or specbindingflags)
            If fi Is Nothing Then Return false
            fi.SetValue(instance, value)
            Return True
        Catch ex As Exception
            Return False
        End Try
    End Function
End Module

use: SetFieldValue(Of cartonclass, Integer)(cartonyoudropped, "survivingeggcount", 3)