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Java™ Platform
Standard Ed. 8
javax.swing

Class JLayeredPane

  • All Implemented Interfaces:
    ImageObserver, MenuContainer, Serializable, Accessible
    Direct Known Subclasses:
    JDesktopPane 

    public class JLayeredPane
extends JComponent
implements Accessible
    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.

    [画像:The following text describes this image.]

    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 JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

    • Field Detail

      • DEFAULT_LAYER

        public static final Integer DEFAULT_LAYER
        Convenience object defining the Default layer. Equivalent to new Integer(0).

      • PALETTE_LAYER

        public static final Integer PALETTE_LAYER
        Convenience object defining the Palette layer. Equivalent to new Integer(100).

      • MODAL_LAYER

        public static final Integer MODAL_LAYER
        Convenience object defining the Modal layer. Equivalent to new Integer(200).

      • POPUP_LAYER

        public static final Integer POPUP_LAYER
        Convenience object defining the Popup layer. Equivalent to new Integer(300).

      • DRAG_LAYER

        public static final Integer DRAG_LAYER
        Convenience object defining the Drag layer. Equivalent to new Integer(400).

      • FRAME_CONTENT_LAYER

        public static final Integer FRAME_CONTENT_LAYER
        Convenience object defining the Frame Content layer. This layer is normally only use to position the contentPane and menuBar components of JFrame. Equivalent to new Integer(-30000).
        See Also:
        JFrame

    • Constructor Detail

      • JLayeredPane

        public JLayeredPane()
        Create a new JLayeredPane

    • Method Detail

      • addImpl

        protected void addImpl(Component comp,
 Object constraints,
 int index)
        Description copied from class: Container
        Adds the specified component to this container at the specified index. This method also notifies the layout manager to add the component to this container's layout using the specified constraints object via the addLayoutComponent method.

        The constraints are defined by the particular layout manager being used. For example, the BorderLayout class defines five constraints: BorderLayout.NORTH, BorderLayout.SOUTH, BorderLayout.EAST, BorderLayout.WEST, and BorderLayout.CENTER.

        The GridBagLayout class requires a GridBagConstraints object. Failure to pass the correct type of constraints object results in an IllegalArgumentException.

        If the current layout manager implements LayoutManager2, then LayoutManager2.addLayoutComponent(Component,Object) is invoked on it. If the current layout manager does not implement LayoutManager2, and constraints is a String, then LayoutManager.addLayoutComponent(String,Component) is invoked on it.

        If the component is not an ancestor of this container and has a non-null parent, it is removed from its current parent before it is added to this container.

        This is the method to override if a program needs to track every add request to a container as all other add methods defer to this one. An overriding method should usually include a call to the superclass's version of the method:

        super.addImpl(comp, constraints, index)

        This method changes layout-related information, and therefore, invalidates the component hierarchy. If the container has already been displayed, the hierarchy must be validated thereafter in order to display the added component.

        Overrides:
        addImpl in class Container
        Parameters:
        comp - the component to be added
        constraints - an object expressing layout constraints for this component
        index - the position in the container's list at which to insert the component, where -1 means append to the end
        See Also:
        Container.add(Component), Container.add(Component, int), Container.add(Component, java.lang.Object), Container.invalidate(), LayoutManager, LayoutManager2

      • remove

        public void remove(int index)
        Remove the indexed component from this pane. This is the absolute index, ignoring layers.
        Overrides:
        remove in class Container
        Parameters:
        index - an int specifying the component to remove
        See Also:
        getIndexOf(java.awt.Component)

      • putLayer

        public static void putLayer(JComponent c,
 int layer)
        Sets the layer property on a JComponent. This method does not cause any side effects like setLayer() (painting, add/remove, etc). Normally you should use the instance method setLayer(), in order to get the desired side-effects (like repainting).
        Parameters:
        c - the JComponent to move
        layer - an int specifying the layer to move it to
        See Also:
        setLayer(java.awt.Component, int)

      • getLayer

        public static int getLayer(JComponent c)
        Gets the layer property for a JComponent, it does not cause any side effects like setLayer(). (painting, add/remove, etc) Normally you should use the instance method getLayer().
        Parameters:
        c - the JComponent to check
        Returns:
        an int specifying the component's layer

      • getLayeredPaneAbove

        public static JLayeredPane getLayeredPaneAbove(Component c)
        Convenience method that returns the first JLayeredPane which contains the specified component. Note that all JFrames have a JLayeredPane at their root, so any component in a JFrame will have a JLayeredPane parent.
        Parameters:
        c - the Component to check
        Returns:
        the JLayeredPane that contains the component, or null if no JLayeredPane is found in the component hierarchy
        See Also:
        JFrame, JRootPane

      • setLayer

        public void setLayer(Component c,
 int layer)
        Sets the layer attribute on the specified component, making it the bottommost component in that layer. Should be called before adding to parent.
        Parameters:
        c - the Component to set the layer for
        layer - an int specifying the layer to set, where lower numbers are closer to the bottom

      • setLayer

        public void setLayer(Component c,
 int layer,
 int position)
        Sets the layer attribute for the specified component and also sets its position within that layer.
        Parameters:
        c - the Component to set the layer for
        layer - an int specifying the layer to set, where lower numbers are closer to the bottom
        position - an int specifying the position within the layer, where 0 is the topmost position and -1 is the bottommost position

      • getLayer

        public int getLayer(Component c)
        Returns the layer attribute for the specified Component.
        Parameters:
        c - the Component to check
        Returns:
        an int specifying the component's current layer

      • getIndexOf

        public int getIndexOf(Component c)
        Returns the index of the specified Component. This is the absolute index, ignoring layers. Index numbers, like position numbers, have the topmost component at index zero. Larger numbers are closer to the bottom.
        Parameters:
        c - the Component to check
        Returns:
        an int specifying the component's index

      • moveToFront

        public void moveToFront(Component c)
        Moves the component to the top of the components in its current layer (position 0).
        Parameters:
        c - the Component to move
        See Also:
        setPosition(Component, int)

      • moveToBack

        public void moveToBack(Component c)
        Moves the component to the bottom of the components in its current layer (position -1).
        Parameters:
        c - the Component to move
        See Also:
        setPosition(Component, int)

      • setPosition

        public void setPosition(Component c,
 int position)
        Moves the component to position within its current layer, where 0 is the topmost position within the layer and -1 is the bottommost position.

        Note: Position numbering is defined by java.awt.Container, and is the opposite of layer numbering. Lower position numbers are closer to the top (0 is topmost), and higher position numbers are closer to the bottom.

        Parameters:
        c - the Component to move
        position - an int in the range -1..N-1, where N is the number of components in the component's current layer

      • getPosition

        public int getPosition(Component c)
        Get the relative position of the component within its layer.
        Parameters:
        c - the Component to check
        Returns:
        an int giving the component's position, where 0 is the topmost position and the highest index value = the count count of components at that layer, minus 1
        See Also:
        getComponentCountInLayer(int)

      • highestLayer

        public int highestLayer()
        Returns the highest layer value from all current children. Returns 0 if there are no children.
        Returns:
        an int indicating the layer of the topmost component in the pane, or zero if there are no children

      • lowestLayer

        public int lowestLayer()
        Returns the lowest layer value from all current children. Returns 0 if there are no children.
        Returns:
        an int indicating the layer of the bottommost component in the pane, or zero if there are no children

      • getComponentCountInLayer

        public int getComponentCountInLayer(int layer)
        Returns the number of children currently in the specified layer.
        Parameters:
        layer - an int specifying the layer to check
        Returns:
        an int specifying the number of components in that layer

      • getComponentsInLayer

        public Component[] getComponentsInLayer(int layer)
        Returns an array of the components in the specified layer.
        Parameters:
        layer - an int specifying the layer to check
        Returns:
        an array of Components contained in that layer

      • getComponentToLayer

        protected Hashtable<Component,Integer> getComponentToLayer()
        Returns the hashtable that maps components to layers.
        Returns:
        the Hashtable used to map components to their layers

      • getObjectForLayer

        protected Integer getObjectForLayer(int layer)
        Returns the Integer object associated with a specified layer.
        Parameters:
        layer - an int specifying the layer
        Returns:
        an Integer object for that layer

      • insertIndexForLayer

        protected int insertIndexForLayer(int layer,
 int position)
        Primitive method that determines the proper location to insert a new child based on layer and position requests.
        Parameters:
        layer - an int specifying the layer
        position - an int specifying the position within the layer
        Returns:
        an int giving the (absolute) insertion-index
        See Also:
        getIndexOf(java.awt.Component)

      • paramString

        protected String paramString()
        Returns a string representation of this JLayeredPane. This method is intended to be used only for debugging purposes, and the content and format of the returned string may vary between implementations. The returned string may be empty but may not be null.
        Overrides:
        paramString in class JComponent
        Returns:
        a string representation of this JLayeredPane.

      • getAccessibleContext

        public AccessibleContext getAccessibleContext()
        Gets the AccessibleContext associated with this JLayeredPane. For layered panes, the AccessibleContext takes the form of an AccessibleJLayeredPane. A new AccessibleJLayeredPane instance is created if necessary.
        Specified by:
        getAccessibleContext in interface Accessible
        Overrides:
        getAccessibleContext in class Component
        Returns:
        an AccessibleJLayeredPane that serves as the AccessibleContext of this JLayeredPane
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Java™ Platform
Standard Ed. 8

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