java - 滚动或调整框架大小时，JPanel 中的绘图消失

Question

我有一个无法解决的大问题，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)，它可以工作，但是当我滚动面板或调整框架大小时，绘图就会消失!

我该如何保留该图画？

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

您永远不应该在提供的 swing 函数之外进行绘制，例如 paintComponent(Graphics g)。调整大小或滚动时，组件将被重新绘制。在此过程中，每个涉及的组件的 paintComponent 方法都会被调用。由于您的绘图发生在面板之外，因此面板不会按预期重新绘制。重写 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 ... */
    }
}