滚动或压缩框架时，JPanel中的绘图将消失

Question

我有一个大问题无法解决——我在JFrame中有一个JPanel。在这个面板中，我画了很多东西（比如图表），它是有效的，但当我滚动面板或调整框架大小时，图形就会消失！

我应该如何保留这幅画？

代码：

  private void full_simulation_button(java.awt.event.ActionEvent evt) {
   if (jTextField1.getText().equals("")){
  JOptionPane jop2 = new JOptionPane();
  jop2.showMessageDialog(null, "You should enter you trace file !",         "Attention", JOptionPane.WARNING_MESSAGE);
   }
   else {
  Graphics g = jPanel5.getGraphics();  
g.setColor(Color.RED);
g.drawRect(150,10,100,20);  
g.fillRect(150,10,100,20);
g.drawLine(200,10 , 200, 2000);
g.setColor(Color.BLACK);
g.drawString("UE",190 ,25 );
g.setColor(Color.BLUE); 
g.drawRect(350,10,100,20); 
g.fillRect(350,10,100,20);
g.drawLine(400,10 , 400, 2000);
g.setColor(Color.BLACK);
g.drawString("Node B",380 ,25 );
 g.setColor(Color.GREEN);
g.drawRect(550,10,100,20);    
g.fillRect(550,10,100,20);
g.drawLine(600,10 , 600, 2000);
g.setColor(Color.BLACK);
g.drawString("RNC",590 ,25 );
g.setColor(Color.YELLOW); 
g.drawRect(750,10,100,20);    
g.fillRect(750,10,100,20);
g.drawLine(800,10 , 800, 2000);
g.setColor(Color.BLACK);
g.drawString("CN",790 ,25 );
System.out.println(new java.io.File("").getAbsolutePath());
final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); 
try {
     final DocumentBuilder builder = factory.newDocumentBuilder();      
     final Document document= builder.parse(new File(jTextField1.getText()));
     //Affiche la version de XML
     System.out.println("la version du XML est "+ document.getXmlVersion());
    //Affiche l'encodage
    System.out.println("l'encodage utilisé est"+document.getXmlEncoding()); 
    //Affiche s'il s'agit d'un document standalone      
    System.out.println("le document est standolone:"+document.getXmlStandalone());
    final Element racine = document.getDocumentElement();
    System.out.println("le racime du fichier est :"+racine.getNodeName());
    final NodeList racineNoeuds = racine.getChildNodes();
    final int nbRacineNoeuds = racineNoeuds.getLength();
    for (int i = 0; i<nbRacineNoeuds; i++) {
          if(racineNoeuds.item(i).getNodeType() == Node.ELEMENT_NODE) {
                 final Element nd = (Element) racineNoeuds.item(i);
                 final Node noeud = racineNoeuds.item(i);
                 System.out.println(noeud.getNodeName());

    final NodeList msg = nd.getElementsByTagName("PARA");
    final int nbre = msg.getLength();
    int marge=0;
    int rang =1;
    String type =null;
    String direction=null;
    for(int j = 0; j<nbre ; j++){
        final Element message = (Element) msg.item(j);

        g.setColor(Color.BLACK);
        if ( message.getAttribute("name").equals("Message Type")){ 
        type = message.getAttribute("value");
       // System.out.println(type);
        if (type.startsWith("RRC")){
          g.drawLine(200,50+marge , 600, 50+marge);
          g.drawString(rang+". "+type,220 ,45+marge );
          marge=marge+30;
          rang=rang+1; 
         }
        if (type.startsWith("NBAP")){
          g.drawLine(400,50+marge , 600, 50+marge);
          g.drawString(rang+". "+type,420 ,45+marge );
          marge=marge+30;
          rang=rang+1; 
         }
        if (type.startsWith("RANAP")){
            g.drawLine(600,50+marge , 800, 50+marge);
            g.drawString(rang+". "+type,620 ,45+marge );
            marge=marge+30;
            rang=rang+1; 
         }
        }
        if ( message.getAttribute("name").equals("Message Direction")){ 
        direction = message.getAttribute("value");
        //System.out.println(direction);
        if ((direction.equals("From-UE"))&&(type.startsWith("RRC"))){
          g.drawString(">",595, 50+marge-25 );
          System.out.println(type);
         }
        if ((direction.equals("To-UE"))&&(type.startsWith("RRC"))){
          g.drawString("<",200, 50+marge-25 );
          System.out.println(type);
         }
        if ((direction.equals("From-NodeB"))&&(type.startsWith("NBAP"))){
          g.drawString(">",595, 50+marge-25 );
          System.out.println(type);
         }
        if ((direction.equals("To-NodeB"))&&(type.startsWith("NBAP"))){
          g.drawString("<",400, 50+marge-25 );
          System.out.println(type);
         }
        if ((direction.equals("From-CN"))&&(type.startsWith("RANAP"))){
          g.drawString("<",600, 50+marge-25 );
          System.out.println(type);
         }
        if ((direction.equals("To-CN"))&&(type.startsWith("RANAP"))){
          g.drawString(">",795, 50+marge-25 );
          System.out.println(type);
         }
  }
}
         }   
}
}
        catch (final ParserConfigurationException e) {
         e.printStackTrace();
            }
        catch (final SAXException e) {
          e.printStackTrace();
           }
       catch (final IOException e) {
        e.printStackTrace();
         }
           }
          }                                       

Answer 1

您不应该在所提供的swing函数（如paintComponent(Graphics g)）之外进行绘制。调整大小或滚动时，将重新绘制组件。在这个过程中，调用每个相关组件的paintComponent方法。由于绘图发生在面板外部，因此不会按预期重新绘制面板。覆盖paintComponent方法并将所有绘图代码复制到其中。

class MyPanel extends JPanel
{
    @Override
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.setColor(Color.RED);
        g.drawRect(150,10,100,20);  
        g.fillRect(150,10,100,20);
        g.drawLine(200,10 , 200, 2000);
        g.setColor(Color.BLACK);
        g.drawString("UE",190 ,25 );
        /* ... All drawing code ... */
    }
}

Answer 2

每次调整组件大小或在滚动窗格中移动组件时，都会重新绘制。这就是Swing的工作方式。如果您希望面板能够重新绘制其内容，它必须了解它。在这种情况下，应该创建一个扩展JComponent类并重写paintComponent(Graphics)方法的新类。正是这种方法将负责绘制您的图表。

public class Drawer extends JComponent {
    private File source;
    public void setSource(File source) {
        this.source = source;
        repaint();
    }
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (source == null) {
            return;
        }
        g.setColor(Color.RED);
        g.drawRect(150, 10, 100, 20);
        g.fillRect(150, 10, 100, 20);
        g.drawLine(200, 10, 200, 2000);
        g.setColor(Color.BLACK);
        g.drawString("UE", 190, 25);
        g.setColor(Color.BLUE);
        g.drawRect(350, 10, 100, 20);
        g.fillRect(350, 10, 100, 20);
        g.drawLine(400, 10, 400, 2000);
        g.setColor(Color.BLACK);
        g.drawString("Node B", 380, 25);
        g.setColor(Color.GREEN);
        g.drawRect(550, 10, 100, 20);
        g.fillRect(550, 10, 100, 20);
        g.drawLine(600, 10, 600, 2000);
        g.setColor(Color.BLACK);
        g.drawString("RNC", 590, 25);
        g.setColor(Color.YELLOW);
        g.drawRect(750, 10, 100, 20);
        g.fillRect(750, 10, 100, 20);
        g.drawLine(800, 10, 800, 2000);
        g.setColor(Color.BLACK);
        g.drawString("CN", 790, 25);
        System.out.println(new java.io.File("").getAbsolutePath());
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        try {
            final DocumentBuilder builder = factory.newDocumentBuilder();
            final Document document = builder.parse(source);

        } catch (final ParserConfigurationException e) {
            e.printStackTrace();
        } catch (final SAXException e) {
            e.printStackTrace();
        } catch (final IOException e) {
            e.printStackTrace();
        }
    }
}

用Drawer类的实例替换JPanel，并用替换监听器方法的内容

private void full_simulation_button(java.awt.event.ActionEvent evt) {                                        
    if (jTextField1.getText().isEmpty()) {
        JOptionPane.showMessageDialog(null, "You should enter you trace file !", "Attention", JOptionPane.WARNING_MESSAGE);
    } else {
        drawer.setSource(new File(jTextField1.getText()));
    }
}

当用户单击按钮时，将创建一个文件，并将其作为Drawer的源。Drawer重新绘制自己，paintComponent()方法由Swing的内部机制调用。

现在，您应该尝试通过不在每次调用paintComponent()方法时解析XML文件来改进代码（在setSource()中解析它，然后在paintComponent()中使用数据）。