如何讓JPanel使用滾動條來適應大J組件？

Question

我有這個問題，JPanel（contentPane）重新調整（testLabel）GUI組件的大小，只要它們太大而不適合面板，就會變得很小。我已經將滾動條添加到JPanel，但組件仍然重新調整大小而不是使用滾動條。這裏是我的課，我使用帶滾動條的JPanel。

package marsPackage; 

import java.awt.*; 
import javax.swing.*; 

public class DashTab{ 

    private JLabel testLabel; //test label 
    private JLabel testLabel2; 
    private JLabel testLabel3; 
    private JLabel testLabel4; 
    private JPanel dashPanel; //Panel that holds the JTabbedPane tab 
    private JPanel contentPane; // Panel that holds all GUI components 
    private JScrollPane scrollPane; // Scrollpane used on contentPane 

    /* 
    * Constructor 
    * All of your GUI components should be added to 
    * contentPane using the gridBagLayout. 
    */ 

    public DashTab(){ 
    //Creating the dashpanel that holds everything 
    dashPanel = new JPanel(); 
    dashPanel.setBackground(Color.WHITE); 

    //Creating the contentPane that holds all GUI components and 
    //uses vertical/horizontal sidebards as needed 
    contentPane = new JPanel(); 
    contentPane.setBackground(Color.WHITE); 

    //Giving the contentPane the GridBagLayout 
    contentPane.setLayout(new GridBagLayout()); 
    GridBagConstraints g = new GridBagConstraints(); 
    contentPane.setPreferredSize(new Dimension(857, 725)); 

    //Adding scrollPane to Content Pane and adding those two to dashPanel 
    scrollPane = new JScrollPane(contentPane); 
    scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS); 
    scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); 
    scrollPane.setBackground(Color.WHITE); 
    dashPanel.add(scrollPane); 

    /* 
    * You may begin adding your GUI components from this point forward. 
    * Remember to only use GridBagLayout with GridBagConstraints using the 
    * g variable. 
    */ 

    testLabel = new JLabel("Testing Here 1"); 
    testLabel.setPreferredSize(new Dimension(500, 500)); 
    testLabel.setBorder(BorderFactory.createMatteBorder(2, 2, 2, 2, Color.gray)); 
    g.gridx = 0; 
    g.gridy = 0; 
    contentPane.add(testLabel, g); 

    testLabel2 = new JLabel("Testing Here 2"); 
    testLabel2.setPreferredSize(new Dimension(250, 200)); 
    testLabel2.setBorder(BorderFactory.createMatteBorder(2, 2, 2, 2, Color.gray)); 
    g.gridx = 1; 
    g.gridy = 0; 
    contentPane.add(testLabel2, g); 

    testLabel3 = new JLabel("Testing Here 3"); 
    testLabel3.setPreferredSize(new Dimension(200, 200)); 
    testLabel3.setBorder(BorderFactory.createMatteBorder(2, 2, 2, 2, Color.gray)); 
    g.gridx = 1; 
    g.gridy = 1; 
    contentPane.add(testLabel3, g); 

    testLabel4 = new JLabel("Testing Here 4"); 
    testLabel4.setPreferredSize(new Dimension(200, 200)); 
    testLabel4.setBorder(BorderFactory.createMatteBorder(2, 2, 2, 2, Color.gray)); 
    g.gridx = 2; 
    g.gridy = 2; 
    contentPane.add(testLabel4, g); 
    } 

    /** 
    * The getDashTab method returns a DashTab object. 
    * @return a DashTab panel object. 
    */ 

    public JPanel getDashTab(){ 
      return dashPanel; 
    } 
} 

這是上面的代碼看起來像：

每當我刪除contentPane.setPreferredSize(new Dimension(857, 725));面板剛剛伸出和完全忽略滾動條使它看起來像：

Answer 1

contentPane.setPreferredSize（new Dimension（857，725））;

請勿使用setPreferredSize（）方法來設置大小。這是佈局管理器的工作，在這種情況下，GridBagLayout可以確定面板的大小。

當面板的首選大小大於滾動窗格的大小時，滾動條會自動出現。

當GUI元件太大而無法放入面板時，它們會變得非常小。

GridBagLayout將嘗試尊重組件的首選大小。如果首選尺寸大於面板尺寸，則將使用「最小尺寸」組件。在JLabel的情況下，最小尺寸是完全顯示文本所需的空間。

再次，不要嘗試使用setPreferedSize（）方法。