Call a private method using a String in VB.Net

Question

ok I do have class like this.

Namespace mySpace

 Public Class ClassA

     Private Function MethodA(prm AS Boolean) As Boolean
       Return False
     End Function

     Private Function MethodB() As Boolean
       Return False
     End Function

 End Class

 Public Class ClassB

     Private Function MethodC() As Boolean
       Return True
     End Function

     Private Function InvokeA() As Boolean
        Dim methodObj As MethodInfo
        'null pointer except below here
        methodObj = Type.GetType("mySpace.ClassA").GetMethod("MethodA") 
        Dim params As Boolean() = {False}
        Return CBool(methodObj.Invoke(New ClassA(), params)) 
     End Function

 End Class

End Namespace

What I am trying here is to invoke a method from a different class with parameters using its method. But this returns a null pointer exception. Why? Where I went wrong?

score 1 · Accepted Answer · 2013-07-31 11:26:28Z

1

You are doing various things wrong. The following code should work without any problem:

Dim objA As ClassA = New ClassA()
methodObj = objA.GetType().GetMethod("MethodA", BindingFlags.Instance Or BindingFlags.NonPublic)
Dim params As Object() = {False}
methodObj.Invoke(objA, params)

You have various errors which shouldn't allow your code to run at all, namely:

You are retrieving a private method without the adequate BindingFlags.
You are not passing the arguments as Object type.

Additionally, you are not using GetMethod with an instantiated object of ClassA (e.g., objA above) and instance.GetType(); I am not 100% sure that you need to do that (perhaps you can accomplish it as you intend), but performing this step is a pretty quick process and would allow the code above to work without any problem.

edited Jul 31, 2013 at 11:26

answered Jul 31, 2013 at 9:46

user2480047

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12 Comments

sloth Over a year ago

-1 for suggesting to create a new instance to get the type of an instance if the type is already well known (why not just GetType(ClassA)?). Also, you're using the wrong BindingFlags, too. It should be BindingFlags.Instance instead of BindingFlags.CreateInstance

user2480047 Over a year ago

@DominicKexel the bindingFlag was a typo. And I haven't suggested to instantiate a new ClassA, I have said that I wasn't sure. Could you please write a code as you suggest?

user2480047 Over a year ago

@DominicKexel instead critising, you should contribute towards solving the problems, don't you think (haven't either see your solution in the other critic you made). I look forward to your solution.

sloth Over a year ago

Type.GetType("mySpace.ClassA") works fine, or you could just use GetType(ClassA) to get the Type (as I said in my comment).

user2480047 Over a year ago

@DominicKexel I am trying it and it does not work. Could you please, write a code confim that it works as you suggest, otherwise remove your -1?

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