Event Handling

MicroUI generates integer-based events that encode the low-level input type and some data. The application can handle these events in the handleEvent method.

The handleEvent Method

  • Every class that extends Widget inherits the handleEvent() method.

  • Add custom event handling by overriding the handleEvent() method of a widget.

  • As an example, here is the event handling of the Button class:

    @Override
    public boolean handleEvent(int event) {
            int type = Event.getType(event);
            if (type == Pointer.EVENT_TYPE) {
                    int action = Pointer.getAction(event);
                    if (action == Pointer.PRESSED) {
                            setPressed(true);
                    } else if (action == Pointer.RELEASED) {
                            setPressed(false);
                            handleClick();
                            return true;
                    }
            } else if (type == DesktopEventGenerator.EVENT_TYPE) {
                    int action = DesktopEventGenerator.getAction(event);
                    if (action == PointerEventDispatcher.EXITED) {
                            setPressed(false);
                    }
            }
            return super.handleEvent(event);
    }
    
  • It’s important to note that only widgets that are “enabled” will receive input events. One can enable a widget by calling setEnabled(true).

  • In the Button class, the click triggers an action defined by the registered OnClickListener. The handleClick method is where the listener is called:

    public void handleClick() {
        OnClickListener listener = this.onClickListener;
        if (listener != null) {
            listener.onClick();
        }
    }
    

Using Events with Buttons

As an example of usage of the Button class we reuse the code created in the previous step, and add a simple action to the button by adding a OnClickListener.

button.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick() {
        System.out.println("Clicked!");
    }
});

When running the modified sample, this is shown in the console:

=============== [ Initialization Stage ] ===============
=============== [ Converting fonts ] ===============
=============== [ Converting images ] ===============
=============== [ Launching on Simulator ] ===============
Clicked!
Clicked!
Clicked!
Clicked!
Clicked!