我只是无法通过JLayeredPanes的方方面面 . (请参阅我的original question of yesterday . 我一直在研究JLayeredPane教程和API . 这些教程与我最终尝试制作的内容有些不同 .
回到第一个方面,我使用了Oracle的JFrame示例并将其修改为包含分层窗格 .
这是代码:
package components;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/* FrameDemo.java requires no other files. */
public class FrameDemo {
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("FrameDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel mainLayer = new JPanel(new BorderLayout());
mainLayer.setPreferredSize(new Dimension(640, 480));
frame.setContentPane(mainLayer);
frame.getLayeredPane().add(mainLayer, JLayeredPane.DEFAULT_LAYER, 0);
JLabel emptyLabel = new JLabel("LABEL");
emptyLabel.setPreferredSize(new Dimension(320, 240));
mainLayer.add(emptyLabel, BorderLayout.NORTH);
JPanel subLayer = new JPanel(new BorderLayout());
JLabel subLabel = new JLabel("SUBLABEL");
subLabel.setPreferredSize(new Dimension( 200, 100));
subLabel.setBackground(Color.YELLOW);
subLayer.add(subLabel, BorderLayout.SOUTH);
subLayer.setVisible(true);
subLabel.setVisible(true);
frame.getLayeredPane().add(subLayer, JLayeredPane.PALETTE_LAYER, 0);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
为什么不起作用? IOW,为什么子标签不显示?它比主层更高 .
一个想法是为什么我将mainLayer添加到内容窗格和分层窗格?如果我不这样做,什么都不会出现 . 即,通过评论这一行,我只得到一个空白框架 .
// frame.setContentPane(mainLayer);
显然,我不理解某些事情 . 但它是什么?
我应该补充一点,显然,这个简单的演示可以在没有分层窗格的情况下完成 . 但我的最终目标是拥有一个可以以编程方式打开和关闭的图层 . 但我甚至无法让这个简单的案例工作 . 如果我能克服这个驼峰,我认为剩下的会更容易 .
附录:
下面的代码说明了我想要实现的内容,它与下面的TrashGod设置非常相似,并且可以正常运行 . 有一个带有常量层的JLayeredPane(在Integer(0)处分层)和一个最初在Integer(-1)处分层的浮动层,但可以通过Integer(-1)层和Integer(1)之间的F7和F8键击来切换层,从而允许它漂浮在恒定层之上或之下 .
package components;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/* MyLayeredPaneDemo.java requires no other files. */
public class MyLayeredPaneDemo {
private JFrame frame;
private JLayeredPane mainPanel;
private JPanel constantLayer;
private JPanel floatingLayer;
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private MyLayeredPaneDemo() {}
private void createAndShowGUI() {
//Create and set up the window.
this.frame = new JFrame("MyLayeredPaneDemo");
this.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.frame.setPreferredSize(new Dimension(640, 480));
mainPanel = new JLayeredPane();
constantLayer = new JPanel(new BorderLayout(0,0));
floatingLayer = new JPanel(new BorderLayout(0,0));
// constantLayer.setPreferredSize();
constantLayer.setOpaque(true);
constantLayer.setBackground(Color.BLUE);
JLabel constantLabel = new JLabel("MAIN LAYER");
constantLayer.setPreferredSize(new Dimension(640, 480));
constantLayer.add(constantLabel, BorderLayout.CENTER);
JLabel subLabel = new JLabel("SUB LAYER");
floatingLayer.setBackground(Color.YELLOW);
floatingLayer.add(subLabel, BorderLayout.SOUTH);
floatingLayer.setOpaque(true);
floatingLayer.setVisible(true);
floatingLayer.setVisible(true);
subLabel.setBackground(Color.YELLOW);
mainPanel.add(constantLayer, new Integer(0), 0);
constantLayer.setBounds(0,0,640,480);
mainPanel.add(floatingLayer, new Integer(-1), 0);
floatingLayer.setBounds(100, 360, 300, 90 );
frame.add(mainPanel, BorderLayout.CENTER);
//Display the window.
mapKeyToAction(frame.getRootPane(),
JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT,
KeyStroke.getKeyStroke(KeyEvent.VK_F7, 0),
"Hide Layer",
new AbstractAction() {
@Override
public void actionPerformed(ActionEvent e) {
System.out.println("F7 pressed");
mainPanel.setLayer(floatingLayer, new Integer(-1));
}
});
mapKeyToAction(frame.getRootPane(),
JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT,
KeyStroke.getKeyStroke(KeyEvent.VK_F8, 0),
"Show Layer",
new AbstractAction() {
@Override
public void actionPerformed(ActionEvent e) {
System.out.println("F8 pressed");
mainPanel.setLayer(floatingLayer, new Integer(1));
}
});
frame.pack();
frame.setVisible(true);
frame.getRootPane().setFocusable(true);
boolean ok = frame.getRootPane().requestFocusInWindow();
System.out.println("focus ok: " + ok);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
new MyLayeredPaneDemo().createAndShowGUI();
}
});
}
private static void mapKeyToAction(JComponent component,
int whichMap, KeyStroke keystroke,String key, Action action) {
component.getInputMap(whichMap).put(keystroke, key);
component.getActionMap().put(key, action);
}
}
但是,在我的实际案例中,我无法使其工作 . 两者之间的区别在于,在这里,我的JLayeredPane由Frame拥有,而在我的实际应用程序中,我希望JaayeredPane由JPanel拥有,是在Frame的包含层次结构中的某些级别,其大小是由其父节点中的GridBagLoyout设置,因此在调用其构造函数时大小是不可知的,这使得我很难调用我需要对JLayeredPane的子节点执行的setBounds() .
进一步补充 . 我知道Oracle Tutorials提到了case where Layouts rather than absolute positioning is used with a JLayeredPane . 这种情况与我的区别在于,在我的情况下,层在不同层上占据相同的水平空间,而在这种情况下,不同层上的组件占据不同的水平空间 . 这几乎就像我们需要一个3D布局管理器!
2 回答
"By default, a layered pane has no layout manager." - How to Use Layered Panes
附录:我需要避免使用
Frame
的分层窗格,而是在窗口中添加分层窗格 .是的,The Root Pane是
JRootPane
的一个实例,其中包含JLayeredPane
. 特别是"The layered pane contains the menu bar and content pane, and enables Z-ordering of other components."我提出的解决方案,感谢trashgod,我期望这也是一个好建议,就是实现ComponentListener并捕获组件resize事件 . 此时,您可以获取容器的实际边界,并使用它来设置JPanels层的实际边界,这些边界始终与包含它们的组件的边界有某种固定的关系 . 有用 .
Trashgod的解决方案也可行,我相信但我没有尝试过 .