如何在Java中为JComboBox添加分隔符？

I have a JComboBox and would like to have a separator in the list of elements. How do I do this in Java?

我有一个JComboBox，并希望在元素列表中有一个分隔符。我如何用Java做到这一点？

A sample scenario where this would come in handy is when making a combobox for font-family-selection; similar to the font-family-selection-control in Word and Excel. In this case I would like to show the most-used-fonts at the top, then a separator and finally all font-families below the separator in alphabetical order.

这个方便派对的示例场景是为字体系列选择制作组合框时;类似于Word和Excel中的font-family-selection-control。在这种情况下，我想在顶部显示最常用的字体，然后是分隔符，最后按字母顺序显示分隔符下面的所有字体系列。

Can anyone help me with how to do this or is this not possible in Java?

任何人都可以帮助我如何做到这一点，或者这在Java中是不可能的？

3 个解决方案

#1

There is a pretty short tutorial with an example that shows how to use a custom ListCellRenderer on java2s http://www.java2s.com/Code/Java/Swing-Components/BlockComboBoxExample.htm

有一个很简短的教程，其中有一个示例，展示了如何在java2上使用自定义ListCellRenderer http://www.java2s.com/Code/Java/Swing-Components/BlockComboBoxExample.htm

Basically it involves inserting a known placeholder in your list model and when you detect the placeholder in the ListCellRenderer you return an instance of 'new JSeparator(JSeparator.HORIZONTAL)'

基本上它涉及在列表模型中插入已知占位符，当您在​​ListCellRenderer中检测到占位符时，您将返回“new JSeparator（JSeparator.HORIZONTAL）”的实例

#2

By the time I wrote and tested the code below, you probably got lot of better answers...
I don't mind as I enjoyed the experiment/learning (still a bit green on the Swing front).

当我编写并测试下面的代码时，你可能会得到很多更好的答案......我不介意，因为我喜欢实验/学习（在Swing前面仍然有点绿色）。

[EDIT] Three years later, I am a bit less green, and I took in account the valid remarks of bobndrew. I have no problem with the key navigation that just works (perhaps it was a JVM version issue?). I improved the renderer to show highlight, though. And I use a better demo code. The accepted answer is probably better (more standard), mine is probably more flexible if you want a custom separator...

[编辑]三年后，我有点不那么绿了，我考虑到了bobndrew的有效评论。我对正常工作的密钥导航没有任何问题（可能是JVM版本问题？）。不过，我改进了渲染器以显示高光。我使用了更好的演示代码。接受的答案可能更好（更标准），如果你想要一个自定义分隔符，我的可能更灵活...

The base idea is to use a renderer for the items of the combo box. For most items, it is a simple JLabel with the text of the item. For the last recent/most used item, I decorate the JLabel with a custom border drawing a line on its bottom.

基本思想是为组合框的项目使用渲染器。对于大多数项目，它是一个带有项目文本的简单JLabel。对于上一个最近/最常用的项目，我用自定义边框装饰JLabel，在其底部画一条线。

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


@SuppressWarnings("serial")
public class TwoPartsComboBox extends JComboBox
{
  private int m_lastFirstPartIndex;

  public TwoPartsComboBox(String[] itemsFirstPart, String[] itemsSecondPart)
  {
    super(itemsFirstPart);
    m_lastFirstPartIndex = itemsFirstPart.length - 1;
    for (int i = 0; i < itemsSecondPart.length; i++)
    {
      insertItemAt(itemsSecondPart[i], i);
    }

    setRenderer(new JLRenderer());
  }

  protected class JLRenderer extends JLabel implements ListCellRenderer
  {
    private JLabel m_lastFirstPart;

    public JLRenderer()
    {
      m_lastFirstPart = new JLabel();
      m_lastFirstPart.setBorder(new BottomLineBorder());
//      m_lastFirstPart.setBorder(new BottomLineBorder(10, Color.BLUE));
    }

    @Override
    public Component getListCellRendererComponent(
        JList list,
        Object value,
        int index,
        boolean isSelected,
        boolean cellHasFocus)
    {
      if (value == null)
      {
        value = "Select an option";
      }
      JLabel label = this;
      if (index == m_lastFirstPartIndex)
      {
        label = m_lastFirstPart;
      }
      label.setText(value.toString());
      label.setBackground(isSelected ? list.getSelectionBackground() : list.getBackground());
      label.setForeground(isSelected ? list.getSelectionForeground() : list.getForeground());
      label.setOpaque(true);

      return label;
    }
  }
}

Separator class, can be thick, with custom color, etc.

分隔类，可以厚，有自定义颜色等。

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

/**
 * Draws a line at the bottom only.
 * Useful for making a separator in combo box, for example.
 */
@SuppressWarnings("serial")
class BottomLineBorder extends AbstractBorder
{
  private int m_thickness;
  private Color m_color;

  BottomLineBorder()
  {
    this(1, Color.BLACK);
  }

  BottomLineBorder(Color color)
  {
    this(1, color);
  }

  BottomLineBorder(int thickness, Color color)
  {
    m_thickness = thickness;
    m_color = color;
  }

  @Override
  public void paintBorder(Component c, Graphics g,
      int x, int y, int width, int height)
  {
    Graphics copy = g.create();
    if (copy != null)
    {
      try
      {
        copy.translate(x, y);
        copy.setColor(m_color);
        copy.fillRect(0, height - m_thickness, width - 1, height - 1);
      }
      finally
      {
        copy.dispose();
      }
    }
  }

  @Override
  public boolean isBorderOpaque()
  {
    return true;
  }
  @Override
  public Insets getBorderInsets(Component c)
  {
    return new Insets(0, 0, m_thickness, 0);
  }
  @Override
  public Insets getBorderInsets(Component c, Insets i)
  {
    i.left = i.top = i.right = 0;
    i.bottom = m_thickness;
    return i;
  }
}

Test class:

测试类：

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


@SuppressWarnings("serial")
public class TwoPartsComboBoxDemo extends JFrame
{
  private TwoPartsComboBox m_combo;

  public TwoPartsComboBoxDemo()
  {
    Container cont = getContentPane();
    cont.setLayout(new FlowLayout());

    cont.add(new JLabel("Data: ")) ;

    String[] itemsRecent = new String[] { "ichi", "ni", "san" };
    String[] itemsOther = new String[] { "one", "two", "three" };
    m_combo = new TwoPartsComboBox(itemsRecent, itemsOther);

    m_combo.setSelectedIndex(-1);
    cont.add(m_combo);
    m_combo.addActionListener(new ActionListener()
    {
      public void actionPerformed(ActionEvent ae)
      {
        String si = (String) m_combo.getSelectedItem();
        System.out.println(si == null ? "No item selected" : si.toString());
      }
    });

    // Reference, to check we have similar behavior to standard combo
    JComboBox combo = new JComboBox(itemsRecent);
    cont.add(combo);
  }

  /**
   * Start the demo.
   *
   * @param args   the command line arguments
   */
  public static void main(String[] args)
  {
    // turn bold fonts off in metal
    UIManager.put("swing.boldMetal", Boolean.FALSE);

    SwingUtilities.invokeLater(new Runnable()
    {
      public void run()
      {
        JFrame demoFrame = new TwoPartsComboBoxDemo();
        demoFrame.setTitle("Test GUI");
        demoFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        demoFrame.setSize(400, 100);
        demoFrame.setVisible(true);
      }
    });
  }
}

#3

You can use a custom ListCellRenderer which would draw the separator items differently. See docs and a small tutorial.

您可以使用自定义ListCellRenderer，它将以不同方式绘制分隔符项。查看文档和一个小教程。