Java，Swing - JPanel没有像预期的那样出现在JFrame中

Question

我得到了一个叫做PleaseWait的java类，并且想在任务繁重时调用它。当我的程序执行繁重的任务时，在我的actionListener的第一行中，我设置了这个类别的变量setVisible(true)，然后在actionListener的末尾设置了setVisible(true)。

不知怎的，当我调用它的时候，这个类中的JPanel不会出现，它只是一个窗口，标题为set，空白为空白。这里是我的代码：

public class PleaseWait extends JFrame{ 

public PleaseWait(){ 

    Toolkit toolkit = Toolkit.getDefaultToolkit(); 

    Dimension screenDimensions = toolkit.getScreenSize(); 
    setSize(300,100); //set size based on screen size 
    setTitle("Please wait"); 
    Container container = getContentPane(); 
    setLocation(new Point(screenDimensions.width*1/4+200, screenDimensions.height*1/4+200)); //set location based on screen size 

    JPanel panel = new JPanel(); 
    JLabel wait = new JLabel("Please wait"); 
    Dimension buttonsSize = new Dimension(300,100); 
    panel.setPreferredSize(buttonsSize); 
    wait.setPreferredSize(buttonsSize); 
    panel.setLayout(new BorderLayout()); 
    panel.add(wait, BorderLayout.CENTER); 
    container.add(panel); 

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    setResizable(false); //unresizable 
} 

Answer 1

的关键不是在你发布的代码，但在这一行：

，并希望把它当一个沉重的任务正在进行中

您正在运行一个“繁重”任务，并且在运行它时，Swing不会绘制此GUI，因为您可能在Swing事件线程上运行了该任务，并且这样做会冻结线程和你的GUI。

解决方案：使用后台线程（例如可通过SwingWorker获取）来运行“繁重”任务。

其他方的问题：

• 这似乎是一个“依赖”或“子”的窗口关闭主应用程序的。如果是这样，它不应该是JFrame，因为应用程序应该只有一个主应用程序窗口，而应该是一个JDialog。
• 您正在使用setPreferredSize(...)并对组件大小进行了硬编码，这些问题充满了问题。

例如，

import java.awt.*; 
import java.awt.Dialog.ModalityType; 
import java.awt.event.ActionEvent; 
import java.awt.event.KeyEvent; 

import javax.swing.*; 

public class TestPleaseWait { 
    public static void main(String[] args) { 
     SwingUtilities.invokeLater(() -> { 
      MainPanel mainPanel = new MainPanel(); 
      JFrame frame = new JFrame("Application"); 
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
      frame.add(mainPanel); 
      frame.pack(); 
      frame.setLocationRelativeTo(null); 
      frame.setVisible(true); 
     }); 
    } 
} 

@SuppressWarnings("serial") 
class MainPanel extends JPanel { 
    private static final int PREF_W = 600; 
    private static final int PREF_H = 450; 

    public MainPanel() { 
     add(new JButton(new AbstractAction("Without Background Thread") { 
      { 
       putValue(MNEMONIC_KEY, KeyEvent.VK_O); 
      } 

      @Override 
      public void actionPerformed(ActionEvent e) { 
       final PleaseWait wait = new PleaseWait(); 
       wait.setVisible(true); 
       try { 
        Thread.sleep(4000); 
       } catch (InterruptedException e1) { 
       } 
       wait.setVisible(false); 
      } 
     })); 
     add(new JButton(new AbstractAction("With Background Thread") { 
      private JDialog waitDialog = null; 
      private MyWaitPanel myWaitPanel = new MyWaitPanel(); 

      { 
       putValue(MNEMONIC_KEY, KeyEvent.VK_W); 
      } 

      @Override 
      public void actionPerformed(ActionEvent e) { 
       if (waitDialog == null) { 
        Component component = MainPanel.this; 
        Window win = SwingUtilities.getWindowAncestor(component); 
        waitDialog = new JDialog(win, "Please Wait", ModalityType.APPLICATION_MODAL); 
        waitDialog.add(myWaitPanel); 
        waitDialog.pack(); 
        waitDialog.setLocationRelativeTo(win); 
       } 

       new Thread(() -> { 
        try { 
         Thread.sleep(4000); 
        } catch (InterruptedException e1) { 
        } 
        SwingUtilities.invokeLater(() -> { 
         waitDialog.setVisible(false); 
        }); 

       }).start(); 
       waitDialog.setVisible(true); 
      } 
     })); 
    } 

    @Override 
    public Dimension getPreferredSize() { 
     if (isPreferredSizeSet()) { 
      return super.getPreferredSize(); 
     } 
     return new Dimension(PREF_W, PREF_H); 
    } 
} 

@SuppressWarnings("serial") 
class MyWaitPanel extends JPanel { 
    private JProgressBar progressBar = new JProgressBar(); 

    public MyWaitPanel() { 
     progressBar.setIndeterminate(true); 

     JLabel waitLabel = new JLabel("Please Wait", SwingConstants.CENTER); 
     waitLabel.setFont(waitLabel.getFont().deriveFont(Font.BOLD, 40)); 

     int ebGap = 10; 
     setBorder(BorderFactory.createEmptyBorder(ebGap, ebGap, ebGap, ebGap)); 
     setLayout(new BorderLayout(ebGap, ebGap)); 
     add(waitLabel, BorderLayout.PAGE_START); 
     add(progressBar); 
    } 
} 

@SuppressWarnings("serial") 
class PleaseWait extends JFrame { 

    public PleaseWait() { 

     Toolkit toolkit = Toolkit.getDefaultToolkit(); 

     Dimension screenDimensions = toolkit.getScreenSize(); 
     setSize(300, 100); // set size based on screen size 
     setTitle("Please wait"); 
     Container container = getContentPane(); 
     setLocation(new Point(screenDimensions.width * 1/4 + 200, 
       screenDimensions.height * 1/4 + 200)); 

     JPanel panel = new JPanel(); 
     JLabel wait = new JLabel("Please wait"); 
     Dimension buttonsSize = new Dimension(300, 100); 
     panel.setPreferredSize(buttonsSize); 
     wait.setPreferredSize(buttonsSize); 
     panel.setLayout(new BorderLayout()); 
     panel.add(wait, BorderLayout.CENTER); 
     container.add(panel); 

     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     setResizable(false); // unresizable 
    } 
}