如何在 Java 中向 JComboBox 添加分隔符？
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How do I add a separator to a JComboBox in Java?
提问by Alfred B. Thordarson
I have a JComboBoxand 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。我如何在 Java 中做到这一点？
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.
一个可以派上用场的示例场景是为字体系列选择制作组合框；类似于 Word 和 Excel 中的字体系列选择控件。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方的所有字体系列。
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 中是不可能的吗？
采纳答案by pfranza
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
有一个非常简短的教程，其中显示了如何在 java2s http://www.java2s.com/Code/Java/Swing-Components/BlockComboBoxExample.htm上使用自定义 ListCellRenderer
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)'
基本上它涉及在您的列表模型中插入一个已知的占位符，当您在 ListCellRenderer 中检测到占位符时，您将返回一个“new JSeparator(JSeparator.HORIZONTAL)”的实例
回答by PhiLho
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，您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 前端仍然有点绿色）。
[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。我对可以正常工作的键导航没有任何问题（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），如果您想要自定义分隔符，我的答案可能更灵活......
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，它是带有项目文本的简单 JLabel。对于最近/最常用的项目，我用自定义边框装饰 JLabel，在其底部绘制一条线。
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.
分隔符类，可以加厚，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);
}
});
}
}
