GWT ValueChangeHandler and getting before value

Question

I want to get values of my textBox before change its value and after changed its value.

String beforeValue = "";
TextBox textBox = new TextBox();
    textBox.addFocusHandler(new FocusHandler() {

        public void onFocus(final FocusEvent event) {
            beforeValue = textBox.getText();

        }
    });
    textBox.addValueChangeHandler(new ValueChangeHandler<String>() {

        public void onValueChange(final ValueChangeEvent<String> event) {
            System.out.println("Before value is " + beforeValue);
            System.out.println("After value is " + textBox.getText());
        }
    });

As above codes , I need two handlers (FocusHandler and ValueChangeHadler) to get before value and after value . My question is how can I get it by one Handler or another simple and easy way ? I don't want to use two handlers to get it. Any suggestions would be appreciated. Thanks in advance !

Answer 1

Your idea(using 2 handlers) is fair enough but its buggy. I don't think it can be done in a better way. If you want to use a single handler, create a custom class wrapper using the two handlers.

Here is the code for you.

public abstract class MyValueChangeHandler<T> implements ValueChangeHandler<T> {

T prevValue = null;
T value = null;

public MyValueChangeHandler(final ValueBoxBase<T> widget) {
    widget.addFocusHandler(new FocusHandler() {
        public void onFocus(FocusEvent event) {
            prevValue = widget.getValue();
        }
    });
}

@Override
public void onValueChange(ValueChangeEvent<T> event) {
    value = event.getValue();
    onValueChange(value, prevValue);

    // or
    // onValueChange(event, prevValue);

    prevValue = value;
}

public abstract void onValueChange(T value, T prevValue);

// or
// public abstract void onValueChange(ValueChangeEvent<T> event, T prevValue);

}

And you can use it as,

TextBox box = new TextBox();
    box.addValueChangeHandler(new MyValueChangeHandler<String>(box) {
        @Override
        public void onValueChange(String value, String prevValue) {
            Window.alert("Prev Value : " + prevValue + " CurrnetValue: "
                    + value);
        }
    });