将组件放在Glass Pane上

Question

我有一个JLabel的子类,它构成了我GUI的一个组件.我已经实现了将组件从一个容器拖放到另一个容器的能力,但没有任何视觉效果.我想让这个JLabel在项目从一个容器拖动到另一个容器期间跟随光标.我想我可以创建一个玻璃窗格并在那里绘制它.但是,即使我将组件添加到玻璃窗格,将组件设置为可见,并将玻璃窗格设置为可见,并将玻璃窗格设置为不透明,我仍然看不到该组件.我知道该组件有效,因为我可以将其添加到内容窗格并显示它.

如何将组件添加到玻璃窗格？

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最后想出了如何让简单的例子工作.谢谢,@ akf.我能够使这个解决方案适应我原来的问题,允许我删除约60行Java2D代码,这些代码手动呈现JLabel的表示.

package test;

import java.awt.Color;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;

public class MainFrame extends JFrame {

    /**
     * @param args
     */
    public static void main(String[] args) {
        MainFrame mf = new MainFrame();
        mf.setSize(400, 400);
        mf.setLocationRelativeTo(null);
        mf.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        mf.setGlassPane(new JPanel());

        JLabel l = new JLabel();
        l.setText("Hello");
        l.setBorder(new LineBorder(Color.BLACK, 1));
        l.setBounds(10, 10, 50, 20);
        l.setBackground(Color.RED);
        l.setOpaque(true);
        l.setPreferredSize(l.getSize());

        //mf.add(l);
        ((JPanel)mf.getGlassPane()).add(l);
        mf.getGlassPane().setVisible(true);

        mf.setVisible(true);
    }
}

Answer 1

下面的示例代码显示了如何在棋盘上拖动棋子.它使用JLayeredPane而不是玻璃窗格,但我确信这些概念是相同的.那是:

a)将玻璃窗格添加到根窗格
b)使玻璃窗格可见
c)将组件添加到玻璃窗格以确保边界有效
d)使用setLocation()为组件的拖动设置动画

编辑:添加代码以修复SSCCE

JLabel l = new JLabel();
l.setText("Hello");
l.setBorder(new LineBorder(Color.BLACK, 1));
// l.setPreferredSize(l.getSize());
// l.setBounds(10, 10, 50, 20);
((JPanel)mf.getGlassPane()).add(l);

mf.setVisible(true);
mf.getGlassPane().setVisible(true);

使用布局管理器时,您永远不会使用setSize()或setBounds()方法.在您的情况下,您只需将首选大小设置为(0,0),因为这是所有组件的默认大小.

将标签添加到框架时,它会起作用,因为框架内容窗格的默认布局管理器是边框布局,因此将忽略标签的首选大小,并使标签成为框架的大小.

但是,默认情况下,JPanel使用的FlowLayout确实尊重组件的首选大小.由于首选大小为0,因此无需绘画.

此外,玻璃板需要可见,以便进行涂漆.

我建议你阅读Swing教程.有关布局管理器如何工作以及玻璃窗格如何工作以及每个部分都有工作示例的部分.

编辑:下面添加的示例代码:

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class ChessBoard extends JFrame implements MouseListener, MouseMotionListener
{
    JLayeredPane layeredPane;
    JPanel chessBoard;
    JLabel chessPiece;
    int xAdjustment;
    int yAdjustment;

    public ChessBoard()
    {
        Dimension boardSize = new Dimension(600, 600);

        //  Use a Layered Pane for this this application

        layeredPane = new JLayeredPane();
        layeredPane.setPreferredSize( boardSize );
        layeredPane.addMouseListener( this );
        layeredPane.addMouseMotionListener( this );
        getContentPane().add(layeredPane);

        //  Add a chess board to the Layered Pane

        chessBoard = new JPanel();
        chessBoard.setLayout( new GridLayout(8, 8) );
        chessBoard.setPreferredSize( boardSize );
        chessBoard.setBounds(0, 0, boardSize.width, boardSize.height);
        layeredPane.add(chessBoard, JLayeredPane.DEFAULT_LAYER);

        //  Build the Chess Board squares

        for (int i = 0; i < 8; i++)
        {
            for (int j = 0; j < 8; j++)
            {
                JPanel square = new JPanel( new BorderLayout() );
                square.setBackground( (i + j) % 2 == 0 ? Color.red : Color.white );
                chessBoard.add( square );
            }
        }

        // Add a few pieces to the board

        ImageIcon duke = new ImageIcon("dukewavered.gif"); // add an image here

        JLabel piece = new JLabel( duke );
        JPanel panel = (JPanel)chessBoard.getComponent( 0 );
        panel.add( piece );
        piece = new JLabel( duke );
        panel = (JPanel)chessBoard.getComponent( 15 );
        panel.add( piece );
    }

    /*
    **  Add the selected chess piece to the dragging layer so it can be moved
    */
    public void mousePressed(MouseEvent e)
    {
        chessPiece = null;
        Component c =  chessBoard.findComponentAt(e.getX(), e.getY());

        if (c instanceof JPanel) return;

        Point parentLocation = c.getParent().getLocation();
        xAdjustment = parentLocation.x - e.getX();
        yAdjustment = parentLocation.y - e.getY();
        chessPiece = (JLabel)c;
        chessPiece.setLocation(e.getX() + xAdjustment, e.getY() + yAdjustment);

        layeredPane.add(chessPiece, JLayeredPane.DRAG_LAYER);
        layeredPane.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
    }

    /*
    **  Move the chess piece around
    */
    public void mouseDragged(MouseEvent me)
    {
        if (chessPiece == null) return;

        //  The drag location should be within the bounds of the chess board

        int x = me.getX() + xAdjustment;
        int xMax = layeredPane.getWidth() - chessPiece.getWidth();
        x = Math.min(x, xMax);
        x = Math.max(x, 0);

        int y = me.getY() + yAdjustment;
        int yMax = layeredPane.getHeight() - chessPiece.getHeight();
        y = Math.min(y, yMax);
        y = Math.max(y, 0);

        chessPiece.setLocation(x, y);
     }

    /*
    **  Drop the chess piece back onto the chess board
    */
    public void mouseReleased(MouseEvent e)
    {
        layeredPane.setCursor(null);

        if (chessPiece == null) return;

        //  Make sure the chess piece is no longer painted on the layered pane

        chessPiece.setVisible(false);
        layeredPane.remove(chessPiece);
        chessPiece.setVisible(true);

        //  The drop location should be within the bounds of the chess board

        int xMax = layeredPane.getWidth() - chessPiece.getWidth();
        int x = Math.min(e.getX(), xMax);
        x = Math.max(x, 0);

        int yMax = layeredPane.getHeight() - chessPiece.getHeight();
        int y = Math.min(e.getY(), yMax);
        y = Math.max(y, 0);

        Component c =  chessBoard.findComponentAt(x, y);

        if (c instanceof JLabel)
        {
            Container parent = c.getParent();
            parent.remove(0);
            parent.add( chessPiece );
            parent.validate();
        }
        else
        {
            Container parent = (Container)c;
            parent.add( chessPiece );
            parent.validate();
        }
    }

    public void mouseClicked(MouseEvent e) {}
    public void mouseMoved(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}

    public static void main(String[] args)
    {
        JFrame frame = new ChessBoard();
        frame.setDefaultCloseOperation( DISPOSE_ON_CLOSE );
        frame.setResizable( false );
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
     }
}

Answer 2

尽管切向的问题,JLayeredPane 例如通过引用@camickr承认以下适配,其中突出的效果mouseReleased()在现有的组件.

public ChessBoard() {
    ...
    // Add a few pieces to the board
    addPiece(3, 0, "?"); 
    addPiece(4, 0, "?");
    addPiece(3, 7, "?");
    addPiece(4, 7, "?");
}

static Font font = new Font("Sans", Font.PLAIN, 72);

private void addPiece(int col, int row, String glyph) {
    JLabel piece = new JLabel(glyph, JLabel.CENTER);
    piece.setFont(font);
    JPanel panel = (JPanel) chessBoard.getComponent(col + row * 8);
    panel.add(piece);
}

Answer 3

除了已经提供的指向 LayerPane 示例的指针之外，原始代码的问题集中在标签的首选大小的设置上。您可以在 JLabel 调整大小之前设置它，因此您的：

l.setPreferredSize(l.getSize());

是无效的。另一方面，如果您在致电 后拨打该电话setBounds，您将看到您想要的结果。考虑到这一点，重新排序：

l.setPreferredSize(l.getSize());
l.setBounds(10, 10, 50, 20);

看起来像这样：

l.setBounds(10, 10, 50, 20);
l.setPreferredSize(l.getSize());