simpleinternalframe.java

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    public void setContent(Component newContent) {
        Component oldContent = getContent();
        if (hasContent()) {
            remove(oldContent);
        }
        add(newContent, BorderLayout.CENTER);
        firePropertyChange("content", oldContent, newContent);
    }

    /**
     * Answers if the panel is currently selected (or in other words active) or not. In the selected state,
     * the header background will be rendered differently.
     * 
     * @return boolean a boolean, where true means the frame is selected (currently active) and false means it
     *         is not
     */
    public boolean isSelected() {
        return isSelected;
    }

    /**
     * This panel draws its title bar differently if it is selected, which may be used to indicate to the user
     * that this panel has the focus, or should get more attention than other simple internal frames.
     * 
     * @param newValue a boolean, where true means the frame is selected (currently active) and false means it
     *            is not
     */
    public void setSelected(boolean newValue) {
        boolean oldValue = isSelected();
        isSelected = newValue;
        updateHeader();
        firePropertyChange("selected", oldValue, newValue);
    }

    public void addHeaderListener(MouseListener listener) {
        gradientPanel.addMouseListener(listener);
    }
        
    // Building *************************************************************

    /**
     * Creates and answers the header panel, that consists of: an icon, a title label, a tool bar, and a
     * gradient background.
     * 
     * @param label the label to paint the icon and text
     * @param bar the panel's tool bar
     * @return the panel's built header area
     */
    private JPanel buildHeader(JLabel label, JToolBar bar) {
        gradientPanel = new GradientPanel(new BorderLayout(), getHeaderBackground());
        label.setOpaque(false);

        gradientPanel.add(label, BorderLayout.WEST);
        gradientPanel.setBorder(BorderFactory.createEmptyBorder(3, 4, 3, 1));

        headerPanel = new JPanel(new BorderLayout());
        headerPanel.add(gradientPanel, BorderLayout.CENTER);
        setToolBar(bar);
        headerPanel.setBorder(new RaisedHeaderBorder());
        headerPanel.setOpaque(false);
        return headerPanel;
    }

    /**
     * Updates the header.
     */
    private void updateHeader() {
        gradientPanel.setBackground(getHeaderBackground());
        gradientPanel.setOpaque(isSelected());
        titleLabel.setForeground(getTextForeground(isSelected()));
        headerPanel.repaint();
        
        Dimension minSize = new Dimension(headerPanel.getMinimumSize());
        minSize.height += 3; // border
        setMinimumSize(minSize);
    }

    /**
     * Updates the UI. In addition to the superclass behavior, we need to update the header component.
     */
    public void updateUI() {
        super.updateUI();
        if (titleLabel != null) {
            updateHeader();
        }
    }

    // Helper Code **********************************************************

    /**
     * Checks and answers if the panel has a content component set.
     * 
     * @return true if the panel has a content, false if it's empty
     */
    private boolean hasContent() {
        return getComponentCount() > 1;
    }

    /**
     * Determines and answers the header's text foreground color. Tries to lookup a special color from the
     * L&F. In case it is absent, it uses the standard internal frame forground.
     * 
     * @param selected true to lookup the active color, false for the inactive
     * @return the color of the foreground text
     */
    protected Color getTextForeground(boolean selected) {
        Color c = UIManager.getColor(selected ? "SimpleInternalFrame.activeTitleForeground"
            : "SimpleInternalFrame.inactiveTitleForeground");
        if (c != null) {
            return c;
        }
        return UIManager.getColor(selected ? "InternalFrame.activeTitleForeground" : "Label.foreground");

    }

    /**
     * Determines and answers the header's background color. Tries to lookup a special color from the L&F.
     * In case it is absent, it uses the standard internal frame background.
     * 
     * @return the color of the header's background
     */
    protected Color getHeaderBackground() {
        Color c = UIManager.getColor("SimpleInternalFrame.activeTitleBackground");
        if (c != null)
            return c;
        if (LookUtils.IS_LAF_WINDOWS_XP_ENABLED)
            c = UIManager.getColor("InternalFrame.activeTitleGradient");
        return c != null ? c : UIManager.getColor("InternalFrame.activeTitleBackground");
    }

    public Component getDragHandle() {
        return gradientPanel;
    }
    
    // Helper Classes *******************************************************

    // A custom border for the raised header pseudo 3D effect.
    private static class RaisedHeaderBorder extends AbstractBorder {

        private static final Insets INSETS = new Insets(1, 1, 1, 0);

        public Insets getBorderInsets(Component c) {
            return INSETS;
        }

        public void paintBorder(Component c, Graphics g, int x, int y, int w, int h) {

            g.translate(x, y);
            g.setColor(UIManager.getColor("controlLtHighlight"));
            g.fillRect(0, 0, w, 1);
            g.fillRect(0, 1, 1, h - 1);
            g.setColor(UIManager.getColor("controlShadow"));
            g.fillRect(0, h - 1, w, 1);
            g.translate(-x, -y);
        }
    }

    // A panel with a horizontal gradient background.
    private static class GradientPanel extends JPanel {

        private GradientPanel(LayoutManager lm, Color background) {
            super(lm);
            setBackground(background);
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (!isOpaque()) {
                return;
            }
            Color control = UIManager.getColor("control");
            int width = getWidth();
            int height = getHeight();

            Graphics2D g2 = (Graphics2D) g;
            Paint storedPaint = g2.getPaint();
            g2.setPaint(new GradientPaint(0, 0, getBackground(), width, 0, control));
            g2.fillRect(0, 0, width, height);
            g2.setPaint(storedPaint);
        }
    }

    private static class ShadowBorder extends AbstractBorder {
        private static final Insets INSETS = new Insets(1, 1, 3, 3);

        public Insets getBorderInsets(Component c) {
            return INSETS;
        }

        public void paintBorder(Component c, Graphics g, int x, int y, int w, int h) {

            Color shadow = UIManager.getColor("controlShadow");
            if (shadow == null) {
                shadow = Color.GRAY;
            }
            Color lightShadow = new Color(shadow.getRed(), shadow.getGreen(), shadow.getBlue(), 170);
            Color lighterShadow = new Color(shadow.getRed(), shadow.getGreen(), shadow.getBlue(), 70);
            g.translate(x, y);

            g.setColor(shadow);
            g.fillRect(0, 0, w - 3, 1);
            g.fillRect(0, 0, 1, h - 3);
            g.fillRect(w - 3, 1, 1, h - 3);
            g.fillRect(1, h - 3, w - 3, 1);
            // Shadow line 1
            g.setColor(lightShadow);
            g.fillRect(w - 3, 0, 1, 1);
            g.fillRect(0, h - 3, 1, 1);
            g.fillRect(w - 2, 1, 1, h - 3);
            g.fillRect(1, h - 2, w - 3, 1);
            // Shadow line2
            g.setColor(lighterShadow);
            g.fillRect(w - 2, 0, 1, 1);
            g.fillRect(0, h - 2, 1, 1);
            g.fillRect(w - 2, h - 2, 1, 1);
            g.fillRect(w - 1, 1, 1, h - 2);
            g.fillRect(1, h - 1, w - 2, 1);
            g.translate(-x, -y);
        }

    }
    
    
}