Question using slider values from GUI component

So I was wondering, how do you guys typically extract the slider values from a GUI component in order to affect changes in audio processing in a audio plugin? I get that the slidervaluechanged function will set the variables to the slider values but how do you pass that information on to the PluginProcessor? Would you have to make those member variables public in order to pass them to the PluginProcessor or is there a more acceptable way of going about it? Also, is it best to implement a slidervaluechanged function in the actual GUI component itself or the parent PluginEditor object?

Maybe have a look at the tutorials:

My favourite approach is the AudioProcessorValueTreeState

But there are also the old method described in the Adding Plugin Parameters tutorial