JScrollPane中不设置它的滚动条的位置属性立即

Question

我有一个JScrollPane显示JPanel，已添加到它（在BoxLayout.Y_AXIS布局，即垂直向下）小包含一些文字与标题和边框JPanel秒。

当这个被创建，如果JScrollPane较大JPanel使用起来比可视，从而出现垂直滚动更多的空间，我JScrollPane不一定它的滚动设置为最高。

修复此问题包括设置JScrollPanel的value属性，该属性是存储滚动距离的属性。但是，将元素添加到JScrollPane，然后将此JScrollPane添加到它所属的帧中后，其位置属性（如值，最大值，最小值）尚未设置，因此我无法将value设置为零因为它已经是零，在此之前意识到它不是零。

下面是我为创建问题而创建的一个小型评论程序。

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.Font; 

import javax.swing.BorderFactory; 
import javax.swing.BoxLayout; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.JScrollBar; 
import javax.swing.JScrollPane; 
import javax.swing.JTextArea; 
import javax.swing.SwingUtilities; 
import javax.swing.border.CompoundBorder; 
import javax.swing.border.EmptyBorder; 
import javax.swing.border.EtchedBorder; 
import javax.swing.border.TitledBorder; 

public class App 
{ 
    public static void main (String[] args) 
    { 
     SwingUtilities.invokeLater(new Runnable() 
     { 
      @Override 
      public void run() 
      { 
       new App(); 
      } 
     }); 
    } 

    public App() 
    { 
     // Making the main window. 
     JFrame window = new JFrame(); 
     window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     window.setSize(200, 200); 
     window.setLayout(
       new BoxLayout(window.getContentPane(), BoxLayout.Y_AXIS)); 

     // Making the JPanel that the scrollbox will be on. 
     JPanel scrollBoxPanel = new JPanel(); 
     scrollBoxPanel 
       .setLayout(new BoxLayout(scrollBoxPanel, BoxLayout.Y_AXIS)); 
     scrollBoxPanel.setMaximumSize(new Dimension(300, 500)); 

     // Making the JScrollPane. 
     JScrollPane listScroller = new JScrollPane(scrollBoxPanel); 

     // Making some panels of text. 
     JPanel smallPanel; 
     JTextArea textArea; 

     for (int i = 0; i < 3; i++) 
     { 
      smallPanel = new JPanel(); 
      smallPanel.setLayout(new BorderLayout()); 

      textArea = new JTextArea(
        "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum fringilla, augue vitae venenatis venenatis, dui sapien suscipit libero, et malesuada quam odio vel sapien.\n"); 
      textArea.setLineWrap(true); 

      TitledBorder criticalPanelBorder = BorderFactory.createTitledBorder(
        BorderFactory.createEtchedBorder(EtchedBorder.RAISED), 
        "Box " + i, TitledBorder.LEFT, TitledBorder.TOP, 
        new Font(null, Font.BOLD, 14)); 
      smallPanel.setBorder(new CompoundBorder(criticalPanelBorder, 
        new EmptyBorder(5, 5, 5, 5))); 

      smallPanel.add(textArea); 
      scrollBoxPanel.add(smallPanel); 
     } 

     // Adding the JScrollPane to the window and displaying. 
     listScroller.validate(); 
     window.add(listScroller); 
     window.setVisible(true); 

     // Printing the attributes of the JScrollBar. Note that the value prints 
     // as 0, but is not zero in the program. 
     JScrollBar scrollBar = listScroller.getVerticalScrollBar(); 
     System.out.println("Value: " + scrollBar.getValue() + ", Max: " 
       + scrollBar.getMaximum() + ", Min: " + scrollBar.getMinimum()); 

    } 
} 

如何将滚动条的值设置为零？

Answer 1

如何将滚动条的值设置为零？

将代码包装在第二个SwingUtilities.invokeLater（）中。这将确保代码在GUI构建完成后执行。