Re: How to implement HasValue for ListBox?

Not sure I am following "wraps a ListBox rather than extends ListBox really means. Would appreciate if you can provide some explanation. 

But here is what I came up with. 

public class WatchedListBoxesWrap extends ListBox implements HasValue<String> {

    

    /**

     * Flag indicating if the handler have been already initialized or not

     */

    private boolean valueChangeHandlerInitialized;

    /*

     * (non-Javadoc)

     * 

     * @see com.google.gwt.user.client.ui.HasValue#getValue()

     */

    @Override

    public String getValue() {

            return getItemText(getSelectedIndex());

    }

    /*

     * (non-Javadoc)

     * 

     * @see com.google.gwt.user.client.ui.HasValue#setValue(java.lang.Object)

     */

    @Override

    public void setValue(String value) {

            for (int i = 0; i < getItemCount(); i++) {

                    if (getItemText(i).equals(value)) {

                            setSelectedIndex(i);

                            break;

                    }

            }

    }

    /*

     * (non-Javadoc)

     * 

     * @see com.google.gwt.user.client.ui.HasValue#setValue(java.lang.Object,

     * boolean)

     */

    @Override

    public void setValue(String value, boolean arg1) {

            setValue(value);

            if (arg1)

                    ValueChangeEvent.fire(this, value);

    }

    /*

     * (non-Javadoc)

     * 

     * @seecom.google.gwt.event.logical.shared.HasValueChangeHandlers#

     * addValueChangeHandler

     * (com.google.gwt.event.logical.shared.ValueChangeHandler)

     */

    @Override

    public HandlerRegistration addValueChangeHandler(

                    ValueChangeHandler<String> handler) {

            // Initialization code

            if (!valueChangeHandlerInitialized) {

                    valueChangeHandlerInitialized = true;

                    addChangeHandler(new ChangeHandler() {

                            public void onChange(ChangeEvent event) {

                                    ValueChangeEvent.fire(WatchedListBoxesWrap.this, getValue());

                            }

                    });

            }

            return addHandler(handler, ValueChangeEvent.getType());

    }

}

What do you think?

On Friday, February 1, 2013 5:31:57 PM UTC-6, Thomas Broyer wrote:

On Friday, February 1, 2013 11:11:49 PM UTC+1, BM wrote:

Thanks Jens and Thomas! Appreciate your quick response. Always learning new in GWT! 

I am not sure the exact difference between ListBox and ValueListbox.

ValueListBox produces the same DOM as ListBox but is "data oriented", a bit more high-level.

 

I can make a custom ListBox called WrappedListBox which extends ListBox and implements HasValue<String>. I think that is what you are referring here right?

I was more referring to a class that implements HasValue and wraps a ListBox (rather than extends ListBox).

 

But I sometimes get confused that I have to inherit bunch of methods for getValue, SetValue and 

addValueChangeHandler. So do I keep the implementation of getvalue, SetValue and addValueChangeHandler  all blank? and just do implementation of addValueChangeHandler and copy the method implementation of ValueListBox. addValueChangeHandler in that?

http://turbomanage.wordpress.com/2010/04/01/selectonelistbox-for-use-with-gwtmvp/ has an example. 

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