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Java javax.swing Class JLayer<V extends Component>（JDK8）

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Java™ Platform
Standard Ed. 8
javax.swing

Class JLayer<V extends Component>

  • Type Parameters:
    V - the type of JLayer's view component
    All Implemented Interfaces:
    ImageObserver, MenuContainer, PropertyChangeListener, Serializable, EventListener, Accessible, Scrollable 

    public final class JLayer<V extends Component>
extends JComponent
implements Scrollable, PropertyChangeListener, Accessible
    JLayer is a universal decorator for Swing components which enables you to implement various advanced painting effects as well as receive notifications of all AWTEvents generated within its borders.

    JLayer delegates the handling of painting and input events to a LayerUI object, which performs the actual decoration.

    The custom painting implemented in the LayerUI and events notification work for the JLayer itself and all its subcomponents. This combination enables you to enrich existing components by adding new advanced functionality such as temporary locking of a hierarchy, data tips for compound components, enhanced mouse scrolling etc and so on.

    JLayer is a good solution if you only need to do custom painting over compound component or catch input events from its subcomponents.

     import javax.swing.*;
 import javax.swing.plaf.LayerUI;
 import java.awt.*;

 public class JLayerSample {

     private static JLayer<JComponent> createLayer() {
         // This custom layerUI will fill the layer with translucent green
         // and print out all mouseMotion events generated within its borders
         LayerUI<JComponent> layerUI = new LayerUI<JComponent>() {

             public void paint(Graphics g, JComponent c) {
                 // paint the layer as is
                 super.paint(g, c);
                 // fill it with the translucent green
                 g.setColor(new Color(0, 128, 0, 128));
                 g.fillRect(0, 0, c.getWidth(), c.getHeight());
             }

             public void installUI(JComponent c) {
                 super.installUI(c);
                 // enable mouse motion events for the layer's subcomponents
                 ((JLayer) c).setLayerEventMask(AWTEvent.MOUSE_MOTION_EVENT_MASK);
             }

             public void uninstallUI(JComponent c) {
                 super.uninstallUI(c);
                 // reset the layer event mask
                 ((JLayer) c).setLayerEventMask(0);
             }

             // overridden method which catches MouseMotion events
             public void eventDispatched(AWTEvent e, JLayer<? extends JComponent> l) {
                 System.out.println("AWTEvent detected: " + e);
             }
         };
         // create a component to be decorated with the layer
         JPanel panel = new JPanel();
         panel.add(new JButton("JButton"));

         // create the layer for the panel using our custom layerUI
         return new JLayer<JComponent>(panel, layerUI);
     }

     private static void createAndShowGUI() {
         final JFrame frame = new JFrame();
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

         // work with the layer as with any other Swing component
         frame.add(createLayer());

         frame.setSize(200, 200);
         frame.setLocationRelativeTo(null);
         frame.setVisible(true);
     }

     public static void main(String[] args) throws Exception {
         SwingUtilities.invokeAndWait(new Runnable() {
             public void run() {
                 createAndShowGUI();
             }
         });
     }
 }
    Note: JLayer doesn't support the following methods: using any of of them will cause UnsupportedOperationException to be thrown, to add a component to JLayer use setView(Component) or setGlassPane(JPanel).
    Since:
    1.7
    See Also:
    JLayer(Component), setView(Component), getView(), LayerUI, JLayer(Component, LayerUI), setUI(javax.swing.plaf.LayerUI), getUI()

    • Method Detail

      • getView

        public V getView()
        Returns the JLayer's view component or null.
        This is a bound property.
        Returns:
        the JLayer's view component or null if none exists
        See Also:
        setView(Component)

      • setView

        public void setView(V view)
        Sets the JLayer's view component, which can be null.
        This is a bound property.
        Parameters:
        view - the view component for this JLayer
        See Also:
        getView()

      • setUI

        public void setUI(LayerUI<? super V> ui)
        Sets the LayerUI which will perform painting and receive input events for this JLayer.
        Parameters:
        ui - the LayerUI for this JLayer

      • getUI

        public LayerUI<? super V> getUI()
        Returns the LayerUI for this JLayer.
        Returns:
        the LayerUI for this JLayer

      • getGlassPane

        public JPanel getGlassPane()
        Returns the JLayer's glassPane component or null.
        This is a bound property.
        Returns:
        the JLayer's glassPane component or null if none exists
        See Also:
        setGlassPane(JPanel)

      • setGlassPane

        public void setGlassPane(JPanel glassPane)
        Sets the JLayer's glassPane component, which can be null.
        This is a bound property.
        Parameters:
        glassPane - the glassPane component of this JLayer
        See Also:
        getGlassPane()

      • createGlassPane

        public JPanel createGlassPane()
        Called by the constructor methods to create a default glassPane. By default this method creates a new JPanel with visibility set to true and opacity set to false.
        Returns:
        the default glassPane

      • setBorder

        public void setBorder(Border border)
        A non-null border, or non-zero insets, isn't supported, to prevent the geometry of this component from becoming complex enough to inhibit subclassing of LayerUI class. To create a JLayer with a border, add it to a JPanel that has a border.

        Note: If border is non-null, this method will throw an exception as borders are not supported on a JLayer.

        Overrides:
        setBorder in class JComponent
        Parameters:
        border - the Border to set
        Throws:
        IllegalArgumentException - this method is not supported
        See Also:
        Border, CompoundBorder

      • addImpl

        protected void addImpl(Component comp,
                       Object constraints,
                       int index)
        This method is not supported by JLayer and always throws UnsupportedOperationException
        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
        Throws:
        UnsupportedOperationException - this method is not supported
        See Also:
        setView(Component), setGlassPane(JPanel)

      • remove

        public void remove(Component comp)
        Removes the specified component from this container. This method also notifies the layout manager to remove the component from this container's layout via the removeLayoutComponent method.

        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 reflect the changes.

        Overrides:
        remove in class Container
        Parameters:
        comp - the component to be removed
        See Also:
        Container.add(java.awt.Component), Container.invalidate(), Container.validate(), Container.remove(int)

      • removeAll

        public void removeAll()
        Removes all the components from this container. This method also notifies the layout manager to remove the components from this container's layout via the removeLayoutComponent method.

        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 reflect the changes.

        Overrides:
        removeAll in class Container
        See Also:
        Container.add(java.awt.Component), Container.remove(int), Container.invalidate()

      • isOptimizedDrawingEnabled

        public boolean isOptimizedDrawingEnabled()
        The JLayer overrides the default implementation of this method (in JComponent) to return false. This ensures that the drawing machinery will call the JLayer's paint implementation rather than messaging the JLayer's children directly.
        Overrides:
        isOptimizedDrawingEnabled in class JComponent
        Returns:
        false

      • propertyChange

        public void propertyChange(PropertyChangeEvent evt)
        This method gets called when a bound property is changed.
        Specified by:
        propertyChange in interface PropertyChangeListener
        Parameters:
        evt - A PropertyChangeEvent object describing the event source and the property that has changed.

      • setLayerEventMask

        public void setLayerEventMask(long layerEventMask)
        Enables the events from JLayer and all its descendants defined by the specified event mask parameter to be delivered to the LayerUI.eventDispatched(AWTEvent, JLayer) method.

        Events are delivered provided that LayerUI is set for this JLayer and the JLayer is displayable.

        The following example shows how to correctly use this method in the LayerUI implementations:

            public void installUI(JComponent c) {
       super.installUI(c);
       JLayer l = (JLayer) c;
       // this LayerUI will receive only key and focus events
       l.setLayerEventMask(AWTEvent.KEY_EVENT_MASK | AWTEvent.FOCUS_EVENT_MASK);
    }

    public void uninstallUI(JComponent c) {
       super.uninstallUI(c);
       JLayer l = (JLayer) c;
       // JLayer must be returned to its initial state
       l.setLayerEventMask(0);
    }
        By default JLayer receives no events and its event mask is 0.
        Parameters:
        layerEventMask - the bitmask of event types to receive
        See Also:
        getLayerEventMask(), LayerUI.eventDispatched(AWTEvent, JLayer), Component.isDisplayable()

      • getLayerEventMask

        public long getLayerEventMask()
        Returns the bitmap of event mask to receive by this JLayer and its LayerUI.

        It means that LayerUI.eventDispatched(AWTEvent, JLayer) method will only receive events that match the event mask.

        By default JLayer receives no events.

        Returns:
        the bitmask of event types to receive for this JLayer

      • getPreferredScrollableViewportSize

        public Dimension getPreferredScrollableViewportSize()
        Returns the preferred size of the viewport for a view component.

        If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

        Specified by:
        getPreferredScrollableViewportSize in interface Scrollable
        Returns:
        the preferred size of the viewport for a view component
        See Also:
        Scrollable

      • getScrollableBlockIncrement

        public int getScrollableBlockIncrement(Rectangle visibleRect,
                                       int orientation,
                                       int direction)
        Returns a scroll increment, which is required for components that display logical rows or columns in order to completely expose one block of rows or columns, depending on the value of orientation.

        If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

        Specified by:
        getScrollableBlockIncrement in interface Scrollable
        Parameters:
        visibleRect - The view area visible within the viewport
        orientation - Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.
        direction - Less than zero to scroll up/left, greater than zero for down/right.
        Returns:
        the "block" increment for scrolling in the specified direction
        See Also:
        Scrollable

      • getScrollableTracksViewportHeight

        public boolean getScrollableTracksViewportHeight()
        Returns false to indicate that the height of the viewport does not determine the height of the layer, unless the preferred height of the layer is smaller than the height of the viewport.

        If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

        Specified by:
        getScrollableTracksViewportHeight in interface Scrollable
        Returns:
        whether the layer should track the height of the viewport
        See Also:
        Scrollable

      • getScrollableTracksViewportWidth

        public boolean getScrollableTracksViewportWidth()
        Returns false to indicate that the width of the viewport does not determine the width of the layer, unless the preferred width of the layer is smaller than the width of the viewport.

        If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

        Specified by:
        getScrollableTracksViewportWidth in interface Scrollable
        Returns:
        whether the layer should track the width of the viewport
        See Also:
        Scrollable

      • getScrollableUnitIncrement

        public int getScrollableUnitIncrement(Rectangle visibleRect,
                                      int orientation,
                                      int direction)
        Returns a scroll increment, which is required for components that display logical rows or columns in order to completely expose one new row or column, depending on the value of orientation. Ideally, components should handle a partially exposed row or column by returning the distance required to completely expose the item.

        Scrolling containers, like JScrollPane, will use this method each time the user requests a unit scroll.

        If the view component of this layer implements Scrollable, this method delegates its implementation to the view component.

        Specified by:
        getScrollableUnitIncrement in interface Scrollable
        Parameters:
        visibleRect - The view area visible within the viewport
        orientation - Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.
        direction - Less than zero to scroll up/left, greater than zero for down/right.
        Returns:
        The "unit" increment for scrolling in the specified direction. This value should always be positive.
        See Also:
        Scrollable
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Java™ Platform
Standard Ed. 8

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2022, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.

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