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!

Next step: Fonts