如何使组合框中的一个项目不可选择,因为我需要用子主题分隔组合框中项目。
是否可以单独修改特定项目的字体?
jComboBox_btech_course.setFont(new java.awt.Font("Tahoma", 0, 14));
jComboBox_btech_course.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Select Course" }));
jComboBox_btech_course.setName("");
private class theHandler implements ActionListener
{
public void actionPerformed(ActionEvent evt)
{
//BTech courses
if(jComboBox_mtech_dept.getSelectedItem().equals("Civil Engineering"))
{
jComboBox_btech_course.removeAllItems();
jComboBox_btech_course.addItem("Building Construction");
jComboBox_btech_course.addItem("Principle And Practice");
jComboBox_btech_course.addItem("Surveying");
jComboBox_btech_course.addItem("Engineering Geology");
jComboBox_btech_course.addItem("Structural Analysis");
jComboBox_btech_course.addItem("Hydraulic Engineering");
jComboBox_btech_course.addItem("Environmental Engineering");
jComboBox_btech_course.addItem("Structural Design");
jComboBox_btech_course.addItem("Geotechnical Engineering");
/*This item has to be unselectable*/
jComboBox_btech_course.addItem("***Sub-topic***");
jComboBox_btech_course.addItem("Transportation Engineering");
jComboBox_btech_course.addItem("Foundation Engineering");
jComboBox_btech_course.addItem("Estimation & Valuation");
jComboBox_btech_course.addItem("Hydrology & Flood Control");
jComboBox_btech_course.addItem("System Analysis, Project Planning And Construction Management");
jComboBox_btech_course.addItem("Irrigation Engineering");
jComboBox_btech_course.addItem("Computer Application in Civil Engineering");
jComboBox_btech_course.addItem("Planning, Design & Detailing");
}
}
}
前言:在所提出的解决方案中,我假设您希望禁用以"**"
开头的项。您可以根据需要更改此逻辑。在改进版本中,MyComboModel
类(见下文)甚至可以存储哪些项被禁用,从而允许将任意项标记为禁用。
解决您的问题涉及两件事:
1.不允许选择要禁用的项目
为此,您可以使用自定义ComboBoxModel
,并覆盖其setSelectedItem()
方法,如果要选择的项目是禁用的项目,则不执行任何操作:
class MyComboModel extends DefaultComboBoxModel<String> {
public MyComboModel() {}
public MyComboModel(Vector<String> items) {
super(items);
}
@Override
public void setSelectedItem(Object item) {
if (item.toString().startsWith("**"))
return;
super.setSelectedItem(item);
};
}
您可以通过将一个实例传递给JComboBox
构造函数来设置这个新模型:
JComboBox<String> cb = new JComboBox<>(new MyComboModel());
2.用不同字体显示禁用项目
为此,您必须使用自定义ListCellRenderer
,在getListCellRendererComponent()
方法中,您可以为禁用和启用的项目配置不同的视觉外观:
Font f1 = cb.getFont();
Font f2 = new Font("Tahoma", 0, 14);
cb.setRenderer(new DefaultListCellRenderer() {
@Override
public Component getListCellRendererComponent(JList<?> list, Object value,
int index, boolean isSelected, boolean cellHasFocus) {
if (value instanceof JComponent)
return (JComponent) value;
boolean itemEnabled = !value.toString().startsWith("**");
super.getListCellRendererComponent(list, value, index,
isSelected && itemEnabled, cellHasFocus);
// Render item as disabled and with different font:
setEnabled(itemEnabled);
setFont(itemEnabled ? f1 : f2);
return this;
}
});
为了获得所需内容,您需要实现ComboBoxEditor
。
通过这种方式,您可以决定在您的情况下,或者在任何其他情况下
您可以通过添加自定义ItemListener
addItemListener(ItemListener aListener)
并且在该方法中禁用选择或将选择切换到上面的项目左右。