Capture Textfield change from Javafx

Question

Have some event that captures every change that occurs in a Javafx Textfield?

Answer 1

Add a Listener to textProperty of your Textfield:

textField.textProperty().addListener((observable, oldValue, newValue) -> {
    System.out.println("Valor antigo = " + oldValue + ". Valor novo = " + newValue);
});

Answer 2

Ask a little generic because there are several properties of Textfield that can be observed by the programmer. Looking at the documentation we have:

Properties inherited from Textinputcontrol (These are the main):

anchovy, caretPosition, Editable, font, length, promptText, redoable, selectedText, Selection, textFormatter, text, undoable

All these properties have methods with the word Property at the end (ex.: textProperty()). In addition to the above mentioned methods we have 104 properties that can be observed.

I will talk about the properties that are normally treated, what they do and how to capture the changes.

textProperty(): I believe it is the most common. This property involves the inserted/deleted text in the component.

textfield.textProperty().addListener(new ChangeListener<String>() {
    @Override
    public void changed(ObservableValue<? extends String> ov, String oldValue, String newValue) {
        // oldValue = Texto anterior a edição
        // newValue = Texto atual
        System.out.println(newValue);
    }
});

// Código acima usando lambdas
text.textProperty().addListener((ObservableValue<? extends String> ov, String oldValue, String newValue) -> {
    System.out.println(newValue);
});

Obs.: We usually use the Changelistener (as the name indicates it captures changes) but there is the option to use a Invalidationlistener to notify an invalid status.

lengthProperty(): This property involves the size of the component text as the user types/deletes the content.

textfield.lengthProperty().addListener(new ChangeListener<Number>() {
    @Override
    public void changed(ObservableValue<? extends Number> ov, Number oldValue, Number newValue) {
         if(newValue.intValue() > 10)
             System.out.println("Texto muito longo");
    }
});

// Código acima usando lambdas
textfield.lengthProperty().addListener((ObservableValue<? extends Number> ov, Number oldValue, Number newValue) -> {
   if(newValue.intValue() > 10)
       System.out.println("Texto muito longo");
});

As you may have seen, the code for capturing changes is similar across properties. However, Textfield has a particularity in this question that is Textformatter. With it you have the possibility to analyze a change before it is effective (Only for java 8u40+)

textfield.setTextFormatter(new TextFormatter<>(change ->
    {
        if (change.getControlNewText().isEmpty()) {
            return change;
        }

        String text = change.getControlNewText();
        for (int i = 0; i < text.length(); i++){
            if(!Character.isDigit(text.charAt(i))){
                return null;
            }
        }

        return change;
    }));

With the getControlText() and getControlNewText() methods we were able to pick up the current and post-editing text (without the change having been effected yet). The above code cancels (Return null) any change that contains in its text a non-numeric element. I won’t go into details of how to use Textformatter because it is too wide, but you can see examples here.