Take input from other field

I have the following scenario. I have two fields to select, first a field with a java class via a pedefined scope selectable. Now the problem is the second field, it should take the information of the class and should allow a scope of informationen from this class selectable, method names, method parameters etc.

I tried the approach from the Shapes tutorial:

new ListScope(node/Color/.staticFields()) {
  public string getName(node<> child) {
    child : StaticFieldDeclaration.name;
  }
};

and used it for my purpose like:

new ListScope(node/<my_Class>/.methods()) {
  public string getName(node<> child) {
    child : InstanceMethodDeclaration.name;
  }
};

and it works, but the problem the <my_Class> changes depending on what is used on the first field.

I tried this approach:

new ListScope(enclosingNode.ancestor<concept = TestClassRef>.testClass.methods()) {
  public string getName(node<> child) {
    child : InstanceMethodDeclaration.name;
  }
};

But this does return an empty sequence, because the scope initializes instantly when it is created. Just for clarification, "TestClassRef" holds the "testClass" as reference which is a "InstanceMethodDeclaration". Is there anything I'm doing completetly wrong here? I can't find anything in any tutorial or in the documentation.

I appreciate all you help!