Correctly Checking KeyEvents

by Richard Bair | Oct 14, 2011 | Tips n' Tricks

I was just writing a quick little application and I wanted to do something special whenever the user released the enter key inside a TextArea. You might be tempted to do it like this:

final TextArea editor = new TextArea();
editor.setOnKeyReleased(new EventHandler<KeyEvent>() {
    public void handle(KeyEvent t) {
        if (t.getCode() == KeyCode.ENTER) {
            System.out.println(editor.getText());
        }
    }
});

Can anybody spot the problem in this code? It correctly gets the key event, and it only prints out the text if the code of the key event is ENTER. The problem is that it also executes this code if you typed ALT+ENTER, or CTRL+ENTER, or any other combination of modifiers with the key code! JavaFX 2.0 contains a handy little class called KeyCombination which will handle all the annoying checking of key modifiers + key code to see if a specific key event matches. Here is the more correct version:

final TextArea editor = new TextArea();
editor.setOnKeyReleased(new EventHandler<KeyEvent>() {
    final KeyCombination combo = new KeyCodeCombination(KeyCode.ENTER);
    public void handle(KeyEvent t) {
        if (combo.match(t)) {
            System.out.println(editor.getText());
        }
    }
});

One extra line of code, and you get correct matching of the key events. Sweet!