EventListener

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Version 1.0 onwards

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Lets You Pick Up Many Events When Building Widgets

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Put your mouse cursor in the box and use the mouse wheel. The amount that the number will change each click will depend on your settings in Control Panel - Mouse - Wheel - Vertical Scrolling.

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Sources

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• Pretty Much Everything

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Notes

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This is something you should only use if you are subclassing a widget - it's not much use otherwise, you can't addEventListener() to anything I'm aware of.

So, as a builder of widgets, you'd use this to pick up events and use them in ways that you can't do with the ordinarily supported event interfaces

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Code

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package com.roughian.examples.client;

import com.google.gwt.user.client.DOM;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.ui.HorizontalPanel;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.MouseWheelVelocity;

class Demo extends Label
{
    // Scroll position
    private int count = 0;
    public Demo()
    {
        setText("Count = " + count);
        /*
         * You need to 'sink' (register for) the events you want
         */
        sinkEvents(Event.ONMOUSEWHEEL);
        DOM.setStyleAttribute(getElement(), "border", "1px dotted red");
        DOM.setStyleAttribute(getElement(), "padding", "20px");
    }
    public void onBrowserEvent(Event event)
    {
        switch (DOM.eventGetType(event))
        {
        case Event.ONMOUSEWHEEL:
            /*
             * Get the mouse wheel information
             */
            MouseWheelVelocity velocity = new MouseWheelVelocity(event);
            count += velocity.getDeltaY();
            setText("Count = " + count);
            /*
             * Stop the event happening where it usually would. If we don't
             * do this, then the panel this widget is in would scroll if it
             * could
             */
            DOM.eventPreventDefault(event);
            break;
        }
    }
}