JLayeredPane
adds depth to a JFC/Swing container,
allowing components to overlap each other when needed.
An
Integer
object specifies each component's depth in the
container, where higher-numbered components sit "on top" of other
components.
For task-oriented documentation and examples of using layered panes see
How to Use a Layered Pane,
a section in
The Java Tutorial.
For convenience,
JLayeredPane
divides the depth-range
into several different layers. Putting a component into one of those
layers makes it easy to ensure that components overlap properly,
without having to worry about specifying numbers for specific depths:
- DEFAULT_LAYER
- The standard layer, where most components go. This the bottommost
layer.
- PALETTE_LAYER
- The palette layer sits over the default layer. Useful for floating
toolbars and palettes, so they can be positioned above other components.
- MODAL_LAYER
- The layer used for modal dialogs. They will appear on top of any
toolbars, palettes, or standard components in the container.
- POPUP_LAYER
- The popup layer displays above dialogs. That way, the popup windows
associated with combo boxes, tooltips, and other help text will appear
above the component, palette, or dialog that generated them.
- DRAG_LAYER
- When dragging a component, reassigning it to the drag layer ensures
that it is positioned over every other component in the container. When
finished dragging, it can be reassigned to its normal layer.
The
JLayeredPane
methods
moveToFront(Component)
,
moveToBack(Component)
and
setPosition
can be used
to reposition a component within its layer. The
setLayer
method
can also be used to change the component's current layer.
Details
JLayeredPane
manages its list of children like
Container
, but allows for the definition of a several
layers within itself. Children in the same layer are managed exactly
like the normal
Container
object,
with the added feature that when children components overlap, children
in higher layers display above the children in lower layers.
Each layer is a distinct integer number. The layer attribute can be set
on a Component
by passing an Integer
object during the add call.
For example:
layeredPane.add(child, JLayeredPane.DEFAULT_LAYER);
or
layeredPane.add(child, new Integer(10));
The layer attribute can also be set on a Component by calling
layeredPaneParent.setLayer(child, 10)
on the
JLayeredPane
that is the parent of component. The layer
should be set
before adding the child to the parent.
Higher number layers display above lower number layers. So, using
numbers for the layers and letters for individual components, a
representative list order would look like this:
5a, 5b, 5c, 2a, 2b, 2c, 1a
where the leftmost components are closest to the top of the display.
A component can be moved to the top or bottom position within its
layer by calling moveToFront
or moveToBack
.
The position of a component within a layer can also be specified directly.
Valid positions range from 0 up to one less than the number of
components in that layer. A value of -1 indicates the bottommost
position. A value of 0 indicates the topmost position. Unlike layer
numbers, higher position values are lower in the display.
Note: This sequence (defined by java.awt.Container) is the reverse
of the layer numbering sequence. Usually though, you will use moveToFront
,
moveToBack
, and setLayer
.
Here are some examples using the method add(Component, layer, position):
Calling add(5x, 5, -1) results in:
5a, 5b, 5c, 5x, 2a, 2b, 2c, 1a
Calling add(5z, 5, 2) results in:
5a, 5b, 5z, 5c, 5x, 2a, 2b, 2c, 1a
Calling add(3a, 3, 7) results in:
5a, 5b, 5z, 5c, 5x, 3a, 2a, 2b, 2c, 1a
Using normal paint/event mechanics results in 1a appearing at the bottom
and 5a being above all other components.
Note: that these layers are simply a logical construct and LayoutManagers
will affect all child components of this container without regard for
layer settings.
Warning: Swing is not thread safe. For more
information see Swing's Threading
Policy.
Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing. As of 1.4, support for long term storage
of all JavaBeansTM
has been added to the java.beans
package.
Please see XMLEncoder
.