Adding Extra State to Buttons
Recipe 2-1 creates a two-state button, providing visuals for on and off states. At times, you may want to implement buttons with further easy-to-distinguish states. Games provide the most common example of this. Many developers implement buttons that typically showcase four states: locked levels, unlocked-but-not-played, unlocked-and-partially-played, and unlocked-and-mastered.
Recipe 2-1 uses a simple Boolean toggle (the isOn instance variable) to store the on/off state and to select the art used (in the toggleButton: method) based on that state. You can easily expand this example for a wider range of art and button states by storing the state as an integer and providing a switch statement for art selection.
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