The control that we created in this chapter can be easily customized by modifying its class code directly. A better approach might be leveraging on UIKit Appearance, adding more flexibility in the way you (or other developers) can adapt the style of this control without modifying the existent class code. We already discussed this feature in Chapter 2, UI Components Overview – UIKit, while discussing UIKit controls. Let's take a look at how to use this with your custom control now.

Track colors are the elements that we will customize to obtain a better integration of ThermostatSlider with different user interfaces.

The only step to make these properties accessible to UI Appearance is to set them as dynamic, as follows:

dynamic var hotTrackColor = UIColor(red:1.0, green:0.4, blue:0.4, alpha: 1.0)

dynamic var coldTrackColor = UIColor(red:0.4, green:0.6, blue:1.0, alpha: 1.0)

Now, from the view controller implementation, you can override the values using...