java - 用 JLayer 装饰滚动工具栏按钮绘制其边框

Question

我正在尝试用 JLayer 包装一个 JButton 以向其添加一些效果/功能。当我用工具栏中的包装器替换按钮时，它会出于某种原因绘制按钮边框。工具栏已将翻转设置为 true。

为什么会发生这种情况，我该如何预防？

import java.awt.AWTEvent;
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLayer;
import javax.swing.JToolBar;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.plaf.LayerUI;

public class JLayerButton extends JFrame {

    private JToolBar toolbar;
    private JButton button1;
    private JButton button2;
    private JButton button3;

    public JLayerButton() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setTitle("JLayer Button");
        setLayout(new BorderLayout());

        toolbar = new JToolBar();
        toolbar.setFloatable(false);
        toolbar.setRollover(true);
        getContentPane().add(toolbar, BorderLayout.NORTH);

        button1 = new JButton("One");
        button1.setFocusable(false);
        toolbar.add(button1);
        button2 = new JButton("Two");
        button2.setFocusable(false);
        toolbar.add(button2);
        button3 = new JButton("Three");
        button3.setFocusable(false);
        toolbar.add(button3);

        // wrap button2 in JLayer
        int componentIndex = toolbar.getComponentIndex(button2);
        JButtonLayerUI layerUI = new JButtonLayerUI();
        JLayer<JButton> layer = new JLayer<JButton>(button2, layerUI);
        layer.setLayerEventMask(AWTEvent.MOUSE_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK);
        layer.setFocusable(false);
        toolbar.add(layer, componentIndex);

        setSize(300, 200);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) 
            throws ClassNotFoundException, InstantiationException, 
            IllegalAccessException, UnsupportedLookAndFeelException {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new JLayerButton().setVisible(true);
            }
        });
    }

    private static class JButtonLayerUI extends LayerUI<JButton> {

        public JButtonLayerUI() {
        }

        @Override
        public void paint(Graphics g, JComponent c) {
            super.paint(g, c);
        }

        @Override
        protected void processMouseEvent(MouseEvent e, JLayer<? extends JButton> l) {
            onMouseEvent(l, e);
        }

        @Override
        protected void processMouseMotionEvent(MouseEvent e, JLayer<? extends JButton> l) {
            onMouseEvent(l, e);
        }

        private void onMouseEvent(JLayer<? extends JButton> l, MouseEvent e) {
            System.out.println(e);
        }        

    }
}

Answer 1

使用 JLayer 似乎无法实现您想要实现的目标，因为:

从BasicToolBarUI的代码中，我们可以看到那些调用

installRolloverBorders 被调用以在 JToolBar 上安装边框:

public void setRolloverBorders( boolean rollover ) {
        rolloverBorders = rollover;

        if ( rolloverBorders )  {
            installRolloverBorders( toolBar );
        } else  {
            installNonRolloverBorders( toolBar );
        }
    }

installRolloverBorders 在工具栏的每个直接 JComponent 子项(非递归)上调用setBorderToRollover

protected void installRolloverBorders ( JComponent c )  {
        // Put rollover borders on buttons
        Component[] components = c.getComponents();

        for (Component component : components) {
            if (component instanceof JComponent) {
                ((JComponent) component).updateUI();
                setBorderToRollover(component);
            }
        }
    }

最后，setBorderToRollover 仅适用于 AbstractButton 的实例，而您的 JLayer 不是。因此，您的 JLayer 按钮的原始边框根本不受影响。

protected void setBorderToRollover(Component c) {
        if (c instanceof AbstractButton) {
            AbstractButton b = (AbstractButton)c;

            Border border = borderTable.get(b);
            if (border == null || border instanceof UIResource) {
                borderTable.put(b, b.getBorder());
            }

            // Only set the border if its the default border
            if (b.getBorder() instanceof UIResource) {
                b.setBorder(getRolloverBorder(b));
            }

            rolloverTable.put(b, b.isRolloverEnabled()?
                              Boolean.TRUE: Boolean.FALSE);
            b.setRolloverEnabled(true);
        }
    }

总而言之，翻转 效果仅适用于满足这两个条件的组件:

1. 是 JToolBar 的直接子级
2. 是AbstractButton的一个实例

您可能可以推出自己的 BasicToolBarUI 版本并覆盖一些方法以添加递归性，例如，看看是否值得花时间。