Question

I’ve been stuck on this all morning, even though it seems like it should be very easy (wondering if I’m missing something fundamental). I have the following code in a class-

 public class myClass
 {
      private Dispatcher m_Dispatcher;

      private void myMethod() { ... }

      private void invokeTheMethod(object sender, PropertyChangedEventArgs e)
      {
           m_Dispatcher.Invoke(myMethod); //XYZ
      }

 }

The dispatcher is attached to the thread that instance of myClass is running on. The invokeTheMethod method is called from another thread, and I’d like to run myMethod on the thread of m_Dispatcher. However, if I try to run this code, I get an exception at XYZ saying “Object reference not an instance of an object”. Is this because I haven’t declared myMethod in the form of a delegate? – I have tried different ways to declare myMethod as a delegate, but I can’t get any of them to compile. Any suggestions are very much appreciated.

Thanks,
Chris

Answer 1

The error you get

Object reference not an instance of an object (NullReferenceException)

refers to the field m_Dispatcher. It is null. That is why you cannot call the Invoke method on it.

Even if there is an instance of Dispatcher “attached to the thread”, there is no way for myClass to get hold of that instance.

What you could do is to supply the instance of Dispatcher to myClass when you create an instance of myClass. Something like this:

public class myClass
{
  // Here is the 'injection' of the instance in the constructor of this class
  public myClass(Dispatcher dispatcher) {
     m_Dispatcher = dispatcher;
  }

  private Dispatcher m_Dispatcher;

  private void myMethod() { ... }

  private void invokeTheMethod(object sender, PropertyChangedEventArgs e)
  {
       m_Dispatcher.Invoke(myMethod); //XYZ
  }
}

As a side note, you should read up some on coding conventions as your casing is considered wrong by the majority of the C# development community. Here is a good start: http://msdn.microsoft.com/en-us/library/vstudio/w2a9a9s3.aspx