problem with a11y listeners for sun buttons

[pixelzoom]

a11y has introduced a general problem with sun buttons. In button listeners, we need to know whether a button fired due to an event involving accessible input (e.g. keyboard) or pointer. And button listeners are currently provided with no information to make that decisions.

E.g. in ComboBox, here's what we currently had to do:

      // Clicking on the button toggles visibility of the list box
      this.button.addListener( () => {
        if ( !this.listBox.visible ) {
          this.showListBox();
        }
        else {
          this.hideListBox();
        }
      } );

      // Handle button clicks, for a11y
      this.button.addInputListener( {
        click: () => {

          //TODO sun#314 order dependency, requires that button's listener has called showList
          if ( this.listBox.visible ) {
            this.listBox.focus();
          }
        }
      } );

This requires a completely different listener for the button to handle button clicks for a11y, outside of sun/buttons/ listener API. And a11y is not at all integrated (or integratabtle) into a standard button listener.

We need a solution that allows us to write button listeners that handle all forms of input.

[pixelzoom]

In ComboBox, something better might look like:

      // Clicking on the button toggles visibility of the list box
      this.button.addListener( event => {
        if ( !this.listBox.visible ) {
          this.showListBox();
          if ( event.pointer.type === 'a11y' ) {
            this.listBox.focus();
          }
        }
        else {
          this.hideListBox();
          if ( event.pointer.type === 'a11y' ) {
            this.button.focus();
          }
        }
      } );

[pixelzoom]

But see also the problem with if ( event.pointer.type === 'a11y' ), phetsims/scenery#932.

[zepumph]

Looks like this is already solved, @jessegreenberg offered to just clean it up.

[zepumph]

This is not duplicated anymore:

sun/js/ComboBox.ts

Lines 364 to 368 in ee93abe

	// Clicking on the button toggles visibility of the list box
	this.button.addListener( () => {
	this.listBox.visibleProperty.value = !this.listBox.visibleProperty.value;
	this.listBox.visibleProperty.value && this.listBox.focusListItemNode( property.value );
	} );

Also noting that sun buttons use a PressListener now, thus supporting keyboard in addition to mouse touch input.

[jessegreenberg]

OK thanks, you were right @zepumph - I don't see anything else for this issue. There is also SceneryEvent.isFromPDOM if there is a need for code like #463 (comment).