MouseWheelEventpublic class MouseWheelEvent extends MouseEvent | An event which indicates that the mouse wheel was rotated in a component.
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. |
| Fields Summary |
|---|
| private static final sun.awt.DebugHelper | dbg | | public static final int | WHEEL_UNIT_SCROLLConstant representing scrolling by "units" (like scrolling with the
arrow keys) | | public static final int | WHEEL_BLOCK_SCROLLConstant representing scrolling by a "block" (like scrolling
with page-up, page-down keys) | | int | scrollTypeIndicates what sort of scrolling should take place in response to this
event, based on platform settings. Legal values are:
- WHEEL_UNIT_SCROLL
- WHEEL_BLOCK_SCROLL
| | int | scrollAmountOnly valid for scrollType WHEEL_UNIT_SCROLL.
Indicates number of units that should be scrolled per
click of mouse wheel rotation, based on platform settings. | | int | wheelRotationIndicates how far the mouse wheel was rotated. | | private static final long | serialVersionUID |
| Constructors Summary |
|---|
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 id results in
unspecified behavior. This method throws an
IllegalArgumentException if source
is null.
this(source, id, when, modifiers, x, y, 0, 0, clickCount,
popupTrigger, scrollType, scrollAmount, wheelRotation);
| 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 id results in
unspecified behavior. This method throws an
IllegalArgumentException if source
is null.
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.
super(source, id, when, modifiers, x, y, xAbs, yAbs, clickCount,
popupTrigger, MouseEvent.NOBUTTON);
this.scrollType = scrollType;
this.scrollAmount = scrollAmount;
this.wheelRotation = wheelRotation;
if (dbg.on) {
dbg.println("MouseWheelEvent constructor");
}
|
| Methods Summary |
|---|
| 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
return scrollAmount;
| | 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:
- MouseWheelEvent.WHEEL_UNIT_SCROLL
- MouseWheelEvent.WHEEL_BLOCK_SCROLL
return scrollType;
| | 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
getScrollType returns MouseWheelEvent.WHEEL_UNIT_SCROLL.
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);
}
}
return scrollAmount * wheelRotation;
| | public int | getWheelRotation()Returns the number of "clicks" the mouse wheel was rotated.
return wheelRotation;
| | public java.lang.String | paramString()Returns a parameter string identifying this event.
This method is useful for event-logging and for debugging.
String scrollTypeStr = null;
if (getScrollType() == WHEEL_UNIT_SCROLL) {
scrollTypeStr = "WHEEL_UNIT_SCROLL";
}
else if (getScrollType() == WHEEL_BLOCK_SCROLL) {
scrollTypeStr = "WHEEL_BLOCK_SCROLL";
}
else {
scrollTypeStr = "unknown scroll type";
}
return super.paramString()+",scrollType="+scrollTypeStr+
",scrollAmount="+getScrollAmount()+",wheelRotation="+
getWheelRotation();
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