我自定義組件上的JScrollpane沒有更新

Question

我試圖在自定義彈出菜單中上下自動更新滾動窗格上的滾動條。但它不起作用。看看下面我完全可運行的示例，我已經添加了基於自定義JPopupMenu的組件和一個JComboBox進行比較。如您所見，在JComboBox中，滾動窗格會更新其位置，以便當前選定的項目始終可見。但是，這不適用於我的組件，我不知道如何設置。

我SSCCE：

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.FlowLayout; 
import java.awt.GridLayout; 
import java.awt.ScrollPane; 
import java.awt.event.FocusEvent; 
import java.awt.event.FocusListener; 
import java.awt.event.KeyAdapter; 
import java.awt.event.KeyEvent; 
import java.awt.event.KeyListener; 
import java.util.Vector; 

import javax.swing.JComboBox; 
import javax.swing.JFrame; 
import javax.swing.JList; 
import javax.swing.JPopupMenu; 
import javax.swing.JScrollPane; 
import javax.swing.JTextField; 
import javax.swing.SwingUtilities; 


public class ScrollFocus extends JFrame { 

    public static void main(String[] args) { 
     SwingUtilities.invokeLater(new Runnable() { 

      @Override 
      public void run() { 
       new ScrollFocus(); 

      } 
     }); 
    } 

    public ScrollFocus() { 
     this.setLayout(new BorderLayout()); 
     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     Vector<String> values = new Vector<>(); 
     values.add("a"); 
     values.add("b"); 
     values.add("c"); 
     values.add("d"); 
     values.add("e"); 
     values.add("f"); 
     values.add("g"); 
     values.add("h"); 
     values.add("i"); 
     values.add("j"); 
     JComboBox<String> comboBox = new JComboBox<>(values); 
     JScrollPane scrollPane = new JScrollPane(comboBox); 
     this.add(scrollPane, BorderLayout.NORTH); 

     CustomTextField customTextField = new CustomTextField(); 
     this.add(customTextField, BorderLayout.CENTER); 
     pack(); 
     setVisible(true); 
    } 

    class CustomTextField extends JTextField implements FocusListener { 

     private CustomPopup customPopup = new CustomPopup(); 

     public CustomTextField() { 
      this.addFocusListener(this); 
      this.addKeyListener(new KeyAdapter() { 
       @Override 
       public void keyPressed(KeyEvent e) { 
        System.out.println("printing..."); 
        setPopupSize(); 
        setPosition(); 
        customPopup.setVisible(true); 

        if(e.getKeyCode() == KeyEvent.VK_UP) { 
         if(customPopup.index < customPopup.getListSize()) 
          customPopup.setSelectedIndex(customPopup.index--); 
        } 
        else if(e.getKeyCode() == KeyEvent.VK_DOWN){ 
         if(customPopup.index >= 0) 
          customPopup.setSelectedIndex(customPopup.index++); 
        } 
       } 
      }); 
     } 

     public void setPopupSize() { 
      customPopup.setPopupSize(new Dimension(this.getWidth(), 110)); 
     } 

     public void setPosition() { 
      customPopup.setLocation(this.getLocation().x, this.getLocation().y); 
     } 

     @Override 
     public void focusGained(FocusEvent e) { 

     } 

     @Override 
     public void focusLost(FocusEvent e) { 
      customPopup.setVisible(false); 
     } 


     class CustomPopup extends JPopupMenu { 
      String[] values = new String[]{"Value1", "Value2", "Value3", "Value4", "Value5", "Value6", "Value7", 
        "Value8","Value9", "Value10", "Value11", "Value12", "Value13", "Value14", "Value15", "Value16",}; 
      JList<String> list = new JList<>(values); 
      JScrollPane scrollPane = new JScrollPane(list); 
      public int index = 0; 

      public CustomPopup() { 
       this.setLayout(new GridLayout(0,1)); 
       this.add(scrollPane); 
       pack(); 
      } 

      public void setSelectedIndex(int index) { 
       list.setSelectedIndex(index); 
      } 

      public int getListSize() { 
       return values.length; 
      } 
     } 
    } 
} 

Answer 1

在JComboBox中滾動面板更新其位置，所以當前選擇的項目始終是可見的。但是，這不適用於我的組件，我不知道如何設置。

list.setSelectedIndex(index); 
list.ensureIndexIsVisible(index); // added 

此外，不使用的KeyListener。 Swing被設計爲與鍵綁定一起使用。請閱讀有關How to Use Key Bindings的Swing教程的thw部分以獲取更多信息。