How to update a single GUI-controller

What is the quickest way to update a single controller in the UI from within the process ?

I want the MIDI-Keyboard to highlight graphical keys in the GUI.

The simplest way is to send an output parameter change from the processor to the controller.

I tried it without success.
#include “pluginterfaces/vst/ivstparameterchanges.h”
but the compiler still complains that the validator does not pass.
Also in the AGain-Example the VuMeter does not seem to be updated.
do I have a chance to update a normal AnimButton? What do I have to prepare for that?

//--- Write outputs parameter changes----------- noch nicht ready
Steinberg::Vst::IParameterChanges* outParamChanges = data.outputParameterChanges;
    // a new value of VuMeter will be send to the host
    // (the host will send it back in sync to our controller for updating our editor)
    //if (outParamChanges)
        int32 index = 0;//test
Steinberg::Vst::IParamValueQueue* paramQueue = outParamChanges->addParameterData (kReg1, index);
        if (paramQueue)
            int32 index2 = 0;
            paramQueue->addPoint (0, 0.3333, index2);//just for test