An elegant (IMHO) solution to link between parameters and components for JUCE (using AudioProcessorValueTree).

AudioParameterUtilities.cpp

/*
  ==============================================================================

    AudioParameterUtilities.cpp
    Created: 16 Jan 2018 10:34:07am
    Author:  Tal Aviram

  ==============================================================================
*/

#include "AudioParameterUtilities.h"

const char* AudioParameterUtilities::ASSIGNED_PARAMETER_ID = "assigned_param_id";

AudioProcessorValueTreeState::ButtonAttachment* AudioParameterUtilities::createComponentAttachment(AudioProcessorValueTreeState& state, const juce::String& paramId, juce::Button& component) {
    component.getProperties().set(ASSIGNED_PARAMETER_ID, paramId);
    return new AudioProcessorValueTreeState::ButtonAttachment(state, paramId, component);
}

AudioProcessorValueTreeState::SliderAttachment* AudioParameterUtilities::createComponentAttachment(AudioProcessorValueTreeState& state, const juce::String& paramId, juce::Slider& component) {
    component.getProperties().set(ASSIGNED_PARAMETER_ID, paramId);
    return new AudioProcessorValueTreeState::SliderAttachment(state, paramId, component);
}

AudioProcessorValueTreeState::ComboBoxAttachment* AudioParameterUtilities::createComponentAttachment(juce::AudioProcessorValueTreeState& state, const juce::String& paramId, juce::ComboBox& component) {
    component.getProperties().set(ASSIGNED_PARAMETER_ID, paramId);
    return new AudioProcessorValueTreeState::ComboBoxAttachment(state, paramId, component);
}

int AudioParameterUtilities::getControlParameterIndexForComponent(juce::AudioProcessorValueTreeState &state, juce::Component *component) { 
    juce::String paramId = component->getProperties().getWithDefault(ASSIGNED_PARAMETER_ID, "");
    
    // fallback for components that got components inside them (we walk only one parent back, seems sufficient).
    if (paramId.isEmpty())
    {
        auto parent = component->getParentComponent();
        if (parent != nullptr) paramId = parent->getProperties().getWithDefault(ASSIGNED_PARAMETER_ID, "");
    }

    auto param = state.getParameter(paramId);
    return (param != nullptr && paramId.isNotEmpty()) ? state.getParameter(paramId)->getParameterIndex() : -1;
}

AudioParameterUtilities.h

/*
  ==============================================================================

    AudioParameterUtilities.h
    Additional utilities useful for parameters.

    Created: 16 Jan 2018 10:34:07am
    Author:  Tal Aviram

  ==============================================================================
*/

#pragma once

#include "JuceHeader.h"

class AudioParameterUtilities {
public:
    static const char* ASSIGNED_PARAMETER_ID;
    
    static juce::AudioProcessorValueTreeState::ButtonAttachment* createComponentAttachment(AudioProcessorValueTreeState& state, const juce::String& paramId, juce::Button& component);
    static juce::AudioProcessorValueTreeState::SliderAttachment* createComponentAttachment(AudioProcessorValueTreeState& state, const juce::String& paramId, juce::Slider& component);
    static juce::AudioProcessorValueTreeState::ComboBoxAttachment* createComponentAttachment(AudioProcessorValueTreeState& state, const juce::String& paramId, juce::ComboBox& component);

    /**
     Simplifies the use of AudioProcessorEditor::getControlParameterIndexForComponent when using the utility class.
     */
    static int getControlParameterIndexForComponent(juce::AudioProcessorValueTreeState& state, juce::Component* component);
    
};