MouseWheelEvent
Java SE 6
| public class java.awt.event MouseWheelEvent
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Java SE 6 |
A wheel mouse is a mouse which has a wheel in place of the middle button. This wheel can be rotated towards or away from the user. Mouse wheels are most often used for scrolling, though other uses are possible.
A MouseWheelEvent object is passed to every MouseWheelListener
object which registered to receive the "interesting" mouse events using the
component's addMouseWheelListener method. Each such listener
object gets a MouseEvent containing the mouse event.
Due to the mouse wheel's special relationship to scrolling Components, MouseWheelEvents are delivered somewhat differently than other MouseEvents. This is because while other MouseEvents usually affect a change on the Component directly under the mouse cursor (for instance, when clicking a button), MouseWheelEvents often have an effect away from the mouse cursor (moving the wheel while over a Component inside a ScrollPane should scroll one of the Scrollbars on the ScrollPane).
MouseWheelEvents start delivery from the Component underneath the mouse cursor. If MouseWheelEvents are not enabled on the Component, the event is delivered to the first ancestor Container with MouseWheelEvents enabled. This will usually be a ScrollPane with wheel scrolling enabled. The source Component and x,y coordinates will be relative to the event's final destination (the ScrollPane). This allows a complex GUI to be installed without modification into a ScrollPane, and for all MouseWheelEvents to be delivered to the ScrollPane for scrolling.
Some AWT Components are implemented using native widgets which display their own scrollbars and handle their own scrolling. The particular Components for which this is true will vary from platform to platform. When the mouse wheel is moved over one of these Components, the event is delivered straight to the native widget, and not propagated to ancestors.
Platforms offer customization of the amount of scrolling that should take place when the mouse wheel is moved. The two most common settings are to scroll a certain number of "units" (commonly lines of text in a text-based component) or an entire "block" (similar to page-up/page-down). The MouseWheelEvent offers methods for conforming to the underlying platform settings. These platform settings can be changed at any time by the user. MouseWheelEvents reflect the most recent settings.
| version | 1.14 04/07/06 |
| since | 1.4 |
| See also | java.awt.event.MouseWheelListener, java.awt.ScrollPane, setWheelScrollingEnabled(boolean), javax.swing.JScrollPane, setWheelScrollingEnabled(boolean) |
| Fields | |||
|---|---|---|---|
| final public static int | WHEEL_UNIT_SCROLL Constant representing scrolling by "units" (like scrolling with the arrow keys)
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| final public static int | WHEEL_BLOCK_SCROLL Constant representing scrolling by a "block" (like scrolling with page-up, page-down keys)
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| Constructors | |||||||||||||||||||||||||||||||||
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| public | MouseWheelEvent(Component source, int id, long when, int modifiers, int x, int y, int clickCount, boolean popupTrigger, int scrollType, int scrollAmount, int wheelRotation) Constructs a MouseWheelEvent object with the
specified source component, type, modifiers, coordinates,
scroll type, scroll amount, and wheel rotation.
Absolute coordinates xAbs and yAbs are set to source's location on screen plus relative coordinates x and y. xAbs and yAbs are set to zero if the source is not showing. Note that passing in an invalid
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| public | MouseWheelEvent(Component source, int id, long when, int modifiers, int x, int y, int xAbs, int yAbs, int clickCount, boolean popupTrigger, int scrollType, int scrollAmount, int wheelRotation) Constructs a MouseWheelEvent object with the
specified source component, type, modifiers, coordinates,
absolute coordinates, scroll type, scroll amount, and wheel rotation.
Note that passing in an invalid Even if inconsistent values for relative and absolute coordinates are passed to the constructor, the MouseWheelEvent instance is still created and no exception is thrown.
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| Methods | |||
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| public String | paramString() Returns a parameter string identifying this event. This method is useful for event-logging and for debugging.
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| Properties | |||||
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| public int | getScrollAmount() Returns the number of units that should be scrolled per click of mouse wheel rotation. Only valid if getScrollType returns
MouseWheelEvent.WHEEL_UNIT_SCROLL
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| public int | getScrollType() Returns the type of scrolling that should take place in response to this event. This is determined by the native platform. Legal values are:
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| public int | getUnitsToScroll() This is a convenience method to aid in the implementation of the common-case MouseWheelListener - to scroll a ScrollPane or JScrollPane by an amount which conforms to the platform settings. (Note, however, that ScrollPane and
JScrollPane already have this functionality built in.)
This method returns the number of units to scroll when scroll type is
MouseWheelEvent.WHEEL_UNIT_SCROLL, and should only be called if
Direction of scroll, amount of wheel movement, and platform settings for wheel scrolling are all accounted for. This method does not and cannot take into account value of the Adjustable/Scrollable unit increment, as this will vary among scrolling components. A simplified example of how this method might be used in a listener:
mouseWheelMoved(MouseWheelEvent event) {
ScrollPane sp = getScrollPaneFromSomewhere();
Adjustable adj = sp.getVAdjustable()
if (MouseWheelEvent.getScrollType() == WHEEL_UNIT_SCROLL) {
int totalScrollAmount =
event.getUnitsToScroll() *
adj.getUnitIncrement();
adj.setValue(adj.getValue() + totalScrollAmount);
}
}
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| public int | getWheelRotation() Returns the number of "clicks" the mouse wheel was rotated.
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