Question

When using Swig to wrap C++ code, it is possible to add methods to the native C++ type using %extend. It is possible to add methods to the C# wrapper class using %typemap(cscode).

Where a method already exists in the wrapper class, is there a way to add additional lines of code?

For example, my C# wrapper method looks like this:

  public void ItemChanged(CollectionObject collectionObject, string propertyName) {
    mynamespacePINVOKE.mynamespace_DataObjectCollection_ItemChanged(swigCPtr, CollectionObject.getCPtr(collectionObject), propertyName);
    if (mynamespacePINVOKE.SWIGPendingException.Pending) throw mynamespacePINVOKE.SWIGPendingException.Retrieve();
  }

I’d like to add a line of code:

  public void ItemChanged(CollectionObject collectionObject, string propertyName) {
    mynamespacePINVOKE.mynamespace_DataObjectCollection_ItemChanged(swigCPtr, CollectionObject.getCPtr(collectionObject), propertyName);
    if (mynamespacePINVOKE.SWIGPendingException.Pending) throw mynamespacePINVOKE.SWIGPendingException.Retrieve();
    **insert my line of code here**
  }

Answer 1

In order to write your own version you’re going to need to make sure it doesn’t clash with the default one. I think the easiest way to do this would be to make ItemChanged private/protected using %csmethodmodifiers and %rename to hide the default wrapped version that gets generated. Once it’s hidden.

You can then safely write your own version of ItemChanged using a cscode typemap that firstly calls the private version and then calls your additional code as you desire.

This is by far the cleanest way of solving the problem – the only way you’re able to inject code directly into the generated code is as part of the argument/return value marshalling – setting up the arguments that get passed in, cleaning up after or handling the return value. Messing with one of those typemaps to inject some code would be fairly messy.