java - jpanel不显示内容

Question

我正在尝试创建一个通用的“确定/取消”对话框，它可以接受添加两个抽象方法(void ok() 和 void cancel())的子类 JPanel；

这个想法是，当按下“确定”按钮或“取消”按钮时，将调用子类面板上的相应方法。但是，我无法让主框架显示 JPanel。

这是 OkCancelFrame 代码。如果运行，它应该显示一个确定/取消表单，其中包含文本“现在你看到我了”。

import javax.swing.JLabel;

public class OkCancelForm extends javax.swing.JFrame {

    private OkCancelPanel okCancelPanel;

    public OkCancelForm(OkCancelPanel okCancelPanel) {
        this.okCancelPanel = okCancelPanel;
        initComponents();
        mainPanel.add(okCancelPanel);
        mainPanel.revalidate();
        mainPanel.repaint();
        pack();
    }

    private void initComponents() {
        java.awt.GridBagConstraints gridBagConstraints;

        mainPanel = new javax.swing.JPanel();
        javax.swing.JPanel buttonPanel = new javax.swing.JPanel();
        javax.swing.JButton ok = new javax.swing.JButton();
        javax.swing.JButton cancel = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(new java.awt.GridBagLayout());

        mainPanel.setLayout(null);
        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.fill = java.awt.GridBagConstraints.BOTH;
        gridBagConstraints.weightx = 1.0;
        gridBagConstraints.weighty = 1.0;
        gridBagConstraints.insets = new java.awt.Insets(2, 2, 2, 2);
        getContentPane().add(mainPanel, gridBagConstraints);

        buttonPanel.setLayout(new java.awt.GridBagLayout());

        ok.setText("Ok");
        ok.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                okActionPerformed(evt);
            }
        });
        buttonPanel.add(ok, new java.awt.GridBagConstraints());

        cancel.setText("Cancel");
        cancel.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                cancelActionPerformed(evt);
            }
        });
        buttonPanel.add(cancel, new java.awt.GridBagConstraints());

        gridBagConstraints = new java.awt.GridBagConstraints();
        gridBagConstraints.gridx = 0;
        gridBagConstraints.gridy = 1;
        gridBagConstraints.anchor = java.awt.GridBagConstraints.LINE_END;
        gridBagConstraints.insets = new java.awt.Insets(2, 2, 2, 2);
        getContentPane().add(buttonPanel, gridBagConstraints);

        pack();
    }

    private void cancelActionPerformed(java.awt.event.ActionEvent evt) {                                       
        okCancelPanel.cancel();
        this.dispose();
    }                                      

    private void okActionPerformed(java.awt.event.ActionEvent evt) {                                   
        okCancelPanel.ok();
        this.dispose();
    }                                  

    public static void main(String args[]) {
        OkCancelPanel panel = new OkCancelPanel() {
            public void ok() { }
            public void cancel() { }
        };

        panel.add(new JLabel("Now you see me"));

        new OkCancelForm(panel).setVisible(true);
    }

    private javax.swing.JPanel mainPanel;
}

Answer 1

不要使用空布局，因为它会在后面咬你。严重地。您正在使用容器将组件添加到空布局，并且在执行此操作时，如果您不设置组件的大小和位置，它将默认为 0,0 位置和 0, 0 大小。一种解决方案是通过 setBounds(...) 设置组件的边界，但您仍然使用非常不灵活的布局管理器，它基本上将您的 GUI 逼到了角落。只是不要使用它。

<小时/>

编辑
David Postill做了一个很好的评论，您似乎正在尝试重新创建自己的 JOptionPane，为什么不简单地使用已经可用的 JOptionPane 类。您可能不知道可以将自己的 JPanel(或任何 JComponent)填充到 JOptionPane 中。例如下面的代码:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.RenderingHints;

import javax.swing.*;

@SuppressWarnings("serial")
public class OkCancelForm2 extends JPanel {
   private static final int PREF_W = 300;
   private static final int PREF_H = PREF_W;

   public OkCancelForm2() {
      JLabel label = new JLabel("What the Heck?", JLabel.CENTER);
      label.setFont(label.getFont().deriveFont(32f));
      label.setForeground(Color.yellow);

      setLayout(new GridBagLayout());
      add(label);
   }

   // just for fun
   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setPaint(new GradientPaint(0, 0, Color.red, 20, 20, Color.blue, true));
      g2.fillOval(0, 0, 2 * getWidth(), 2 * getHeight());
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      OkCancelForm2 mainPanel = new OkCancelForm2();

      int selection = JOptionPane.showConfirmDialog(null, mainPanel,
            "My OK/Cancel Pane", JOptionPane.OK_CANCEL_OPTION,
            JOptionPane.PLAIN_MESSAGE);

      if (selection == JOptionPane.OK_OPTION) {
         System.out.println("OK selected");
      } else if (selection == JOptionPane.CANCEL_OPTION) {
         System.out.println("Cancel selected");
      } else {
         System.out.println("JOptionPane closed with no button selected");
      }
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

<小时/>

有这些行:

  OkCancelForm2 mainPanel = new OkCancelForm2();

  int selection = JOptionPane.showConfirmDialog(null, mainPanel,
        "My OK/Cancel Pane", JOptionPane.OK_CANCEL_OPTION,
        JOptionPane.PLAIN_MESSAGE);

这会将 JPanel 派生对象 mainPanel 填充到 JOptionPane 中，并生成此 JOptinPane: