使用可编辑组合框时，DefaultListCellRenderer 无法正确呈现空字符串

Posted 2023-02-22

【中文标题】使用可编辑组合框时，DefaultListCellRenderer 无法正确呈现空字符串

【英文标题】：DefaultListCellRenderer does not render empty String correctly when using an editable combo box

【发布时间】：2015-08-25 15:06:44

【问题描述】：

我已将自定义渲染器安装到可编辑的 JCombobox，但渲染空字符串时遇到问题。 您知道如何以正确/相似的高度显示空项目吗？或者这是一个 Java 错误？

请参阅以下示例和屏幕截图以了解区别：

package combo;

import java.awt.Component;
import java.awt.GridLayout;
import java.util.Vector;

import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.SwingUtilities;

public class MyComboBox 

  private final class CustomCellRenderer extends DefaultListCellRenderer 


    private static final long serialVersionUID = 1L;

    @Override
    public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) 
      super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
      return this;
    
  

  private Vector<String> listSomeString = new Vector<String>();
  private JComboBox someComboBox = new JComboBox(listSomeString);
  private JComboBox editableComboBox = new JComboBox(listSomeString);
  private JComboBox non_EditableComboBox = new JComboBox(listSomeString);
  private JFrame frame;

  public MyComboBox() 
    listSomeString.add("");
    listSomeString.add("-");
    listSomeString.add("Snowboarding");
    listSomeString.add("Rowing");
    listSomeString.add("Knitting");
    listSomeString.add("Speed reading");
    someComboBox.setPrototypeDisplayValue("Speed reading");
    someComboBox.setEditable(true);
    editableComboBox.setPrototypeDisplayValue("Speed reading");
    editableComboBox.setEditable(true);
    editableComboBox.setRenderer(new CustomCellRenderer());
    frame = new JFrame();
    frame.setLayout(new GridLayout(0, 1, 10, 10));
    frame.add(someComboBox);
    frame.add(editableComboBox);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocation(100, 100);
    frame.pack();
    frame.setVisible(true);
  

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

      @Override
      public void run() 
        MyComboBox aCTF = new MyComboBox();
      
    );
  

【参考方案1】：

JComboBox 不使用DefaultListCellRenderer。如果你打电话

System.out.println(editableComboBox.getRenderer());

您会注意到，JComboBox 使用了 BasicComboBoxRenderer。

你只需要把它改成

private final class CustomCellRenderer extends BasicComboBoxRenderer
  private static final long serialVersionUID = 1L;

  @Override
  public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) 
    super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
    return this;