java - 为什么JDialog无法正常显示

Question

我创建了一种在对话框中显示消息的方法，但每次运行 java swing 应用程序时对话框的大小都会发生变化，下面是 dailog 屏幕截图的链接:

Improrer Message Box Display
Proper Message Box Display

下面是我为 JDialog Display 创建的方法(SetMSGDialog)

public class DemoClass
{
    private static JDialog MSGDialog;
    private static JPanel MSGPanel;
    private static JLabel MSGLabel;
    private static JButton MSGButton;

    DemoClass()
    {
        MSGDialog = new JDialog(MSGDialog,"Message",JDialog.ModalityType.APPLICATION_MODAL);
        MSGPanel = new JPanel(null);
        MSGLabel = new JLabel();
        MSGButton = new JButton("Close");
    }

    public static void SetMSGDialog(String MSG)
    {
        MSGDialog.setModal(true);
        MSGDialog.setSize(400,125);
        MSGDialog.setResizable(false);
        MSGDialog.setLocationRelativeTo(null);
        MSGLabel.setText(MSG);
        MSGButton.setText("Close");
        MSGLabel.setBounds(25, 25, 375, 30);
        MSGButton.setBounds(160,70,80,30);
        MSGPanel.add(MSGLabel);
        MSGPanel.add(MSGButton);
        MSGDialog.add(MSGPanel);
        MSGDialog.setVisible(true);
    }

    public static void main(String[] args)
    {
        DemoClass MsgBox = new DemoClass();
        MsgBox.SetMSGDialog("Please Login First");
    }
}

请告诉我我做错了什么。我必须做什么才能正确显示 Jdialog。

Answer 1

您问为什么您的 JDialog 无法正常显示，主要原因是您的代码忽略了组件已经使用的布局管理器。一种快速而糟糕的解决方案是使用绝对布局或 null 布局，但不建议将其用于组件放置，因为这会导致 GUI 非常不灵活，尽管它们在单一平台和屏幕分辨率上可能看起来不错，它们在大多数其他平台或屏幕分辨率上看起来很糟糕，并且很难更新和维护。

建议:

• 摆脱 setSize(...)、setBounds(...) 等。
• 使用布局管理器来帮助调整组件的大小和位置。
• 在显示对话框之前打包。
• 不要在程序中过度使用 static 修饰符。
• 您可以执行类似于下面代码的操作，但在显示此代码后，JOptionPane 将是显示此类消息的最简单方法。

---

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Font;
import java.awt.GridBagLayout;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.*;

@SuppressWarnings("serial")
public class DemoClass2 extends JPanel {
   // constants
   private static final String TITLE = "Message";
   private static final float LABEL_POINTS = 24f;
   private static final int L_GAP = 15;
   private static final int B_GAP = 25;

   // static poor man's singlton instance
   private static DemoClass2 demoClass2;
   private JDialog dialog = new JDialog();
   private JLabel label = new JLabel("", SwingConstants.CENTER);

   public DemoClass2() {
      dialog.setModal(true);
      dialog.setTitle(TITLE);

      label.setFont(label.getFont().deriveFont(Font.BOLD, LABEL_POINTS));
      label.setBorder(BorderFactory.createEmptyBorder(L_GAP, L_GAP, L_GAP, L_GAP));

      JPanel btnPanel = new JPanel(new GridBagLayout());
      btnPanel.setBorder(BorderFactory.createEmptyBorder(B_GAP, B_GAP, B_GAP, B_GAP));
      btnPanel.add(new JButton(new DisposeAction("Close", KeyEvent.VK_C)));

      setLayout(new BorderLayout());
      //setBorder(border);
      add(label, BorderLayout.PAGE_START);
      add(btnPanel, BorderLayout.CENTER);

      dialog.getContentPane().add(this);
   }

   private void setMessage(String message) {
      label.setText(message);
   }

   private void display() {
      dialog.setResizable(false);
      dialog.pack();
      dialog.setLocationRelativeTo(null);
      dialog.setVisible(true);
   }

   public void setMessageAndDisplay(String message) {
      setMessage(message);
      display();
   }

   public static void displayMessage(String message) {
      if (demoClass2 == null) {
         demoClass2 = new DemoClass2();
      }
      demoClass2.setMessageAndDisplay(message);
   }

   private class DisposeAction extends AbstractAction {
      public DisposeAction(String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         Component c = (Component) e.getSource();
         if (c == null) {
            return;
         }
         Window win = SwingUtilities.getWindowAncestor(c);
         if (win == null) {
            return;
         }
         win.dispose();         
      }
   }

   private static void createAndShowGui() {
      DemoClass2.displayMessage("Fubars Rule!!!");

      DemoClass2.displayMessage("This is a bit of a longer message. The dialog should get bigger.");
   }

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