raw::UIConnection

This class offers a bidirectional connection between Data and its UI representation.
In order to use it, just add one of these as Member variable in your interface class:

class MyInterface
{
    MyInterface(hise::MainController* mc):
        s("My Funky Slider"),
        connection(&s, mc, "Sine 1", hise::SineSynth::SaturationAmount)
    {
        addAndMakeVisible(s);
        s.setRange(0.0, 1.0, 0.01);
    }

    juce::Slider s;
    raw::UIConnection::Slider connection;
}

If you just want a more generic, but unidirectional connection (Processor->UI) take a look at the Reference class.