MouseWheelListener

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Version 1.4 onwards

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Tells You When The Mouse Wheel Is Scrolled

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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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• FocusPanel
• HTML
• Image
• Label

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This is a listener is fired when the mouse wheel is scrolled. Within the MouseWheelVelocity information, there is getDeltaY which is a signed int indicating how far the wheel moves.

Note that you need DOM.eventPreventDefault(DOM.eventGetCurrentEvent()); or else the event will fall through to the widget underneath and the whole damn screen will scroll at the same time.

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Code

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class Demo extends Label implements MouseWheelListener
{
    // Scroll position
    private int count = 0;
    public Demo()
    {
        setText("Count = " + count);
        addMouseWheelListener(this);
        DOM.setStyleAttribute(getElement(), "border", "1px dotted red");
        DOM.setStyleAttribute(getElement(), "padding", "20px");
    }
    public void onMouseWheel(Widget sender, MouseWheelVelocity velocity)
    {
        count += velocity.getDeltaY();
        setText("Count = " + count);
        DOM.eventPreventDefault(DOM.eventGetCurrentEvent());
    }
}