问题
class RuleComboBox extends JComboBox {
public RuleComboBox() {
super();
this.setModel(new javax.swing.DefaultComboBoxModel(new String[]{"abc", "defg"}));
((JLabel) this.getRenderer()).setHorizontalAlignment(SwingConstants.CENTER);
}
}
The getRenderer() line aligns the text to centre.
When I useruleComboBox1.setEnabled(false) and ruleComboBox1.setEditable(true), the text aligns back to the left which I don't want. How can I stop this?
I should explain that I'm using setEditable(true) to keep the appearance of the text within the ComboBox when I disable it.
回答1:
The editor for a JComboBox must implement the ComboBoxEditor interface. The default implementation extends from BasicComboBoxEditor which returns a JTextField as the editor. A JTextField doesn't support the concept of displaying text centered.
So you can implement your own ComboBoxEditor. I would suggest you can just use the BasicComboBoxEditor and change the code to create a JTextPane instead of a JTextField. Then when you create the text pane you can use:
SimpleAttributeSet center = new SimpleAttributeSet();
StyleConstants.setAlignment(center, StyleConstants.ALIGN_CENTER);
StyledDocument doc = textPane.getStyledDocument();
doc.setParagraphAttributes(0, doc.getLength(), center, false);
which will cause the code to be centered.
Note: this will not be a straight forward conversion. A JTextField invokes an ActionListener when the Enter key is pressed. A JTextPane doesn't support this functionality (the default is to insert a new line) so you will need to replicate this functionality for the JTextPane. That is you will need to use Key Bindings to handle the Enter key. So you will need to wrap the ActionListener in a custom Action and then bind the Enter key to the text pane.
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.border.Border;
import java.awt.Component;
import java.awt.event.*;
import java.lang.reflect.Method;
//import sun.reflect.misc.MethodUtil;
/**
* A custom editor for editable combo boxes. The editor is implemented as a JTextPane.
*
*/
public class TextPaneComboBoxEditor implements ComboBoxEditor {
protected JTextPane editor;
private Object oldValue;
public TextPaneComboBoxEditor() {
editor = createEditorComponent();
}
public Component getEditorComponent() {
return editor;
}
/**
* Creates the internal editor component. Override this to provide
* a custom implementation.
*
* @return a new editor component
* @since 1.6
*/
protected JTextPane createEditorComponent() {
JTextPane editor = new BorderlessTextPane("",9);
editor.setBorder(null);
SimpleAttributeSet center = new SimpleAttributeSet();
StyleConstants.setAlignment(center, StyleConstants.ALIGN_CENTER);
StyledDocument doc = editor.getStyledDocument();
doc.setParagraphAttributes(0, doc.getLength(), center, false);
return editor;
}
/**
* Sets the item that should be edited.
*
* @param anObject the displayed value of the editor
*/
public void setItem(Object anObject) {
String text;
if ( anObject != null ) {
text = anObject.toString();
if (text == null) {
text = "";
}
oldValue = anObject;
} else {
text = "";
}
// workaround for 4530952
if (! text.equals(editor.getText())) {
editor.setText(text);
}
}
public Object getItem() {
Object newValue = editor.getText();
// This code only works for Strings. The default implementation would
// use reflection to create Object of whatever class was stored in the
// ComboBoxModel. You will need to fix the reflection code if you want
// to support other types of data in the model
/*
if (oldValue != null && !(oldValue instanceof String)) {
// The original value is not a string. Should return the value in it's
// original type.
if (newValue.equals(oldValue.toString())) {
return oldValue;
} else {
// Must take the value from the editor and get the value and cast it to the new type.
Class<?> cls = oldValue.getClass();
try {
Method method = MethodUtil.getMethod(cls, "valueOf", new Class[]{String.class});
newValue = MethodUtil.invoke(method, oldValue, new Object[] { editor.getText()});
} catch (Exception ex) {
// Fail silently and return the newValue (a String object)
}
}
}
*/
return newValue;
}
public void selectAll() {
editor.selectAll();
editor.requestFocus();
}
public void addActionListener(ActionListener l) {
// editor.addActionListener(l);
Action enter = new WrappedActionListener(l);
editor.getActionMap().put("insert-break", enter);
}
public void removeActionListener(ActionListener l) {
// editor.removeActionListener(l);
}
static class BorderlessTextPane extends JTextPane {
public BorderlessTextPane(String value,int n) {
// super(value,n);
setText(value);
}
// workaround for 4530952
public void setText(String s) {
if (getText().equals(s)) {
return;
}
super.setText(s);
}
public void setBorder(Border b) {
if (!(b instanceof UIResource)) {
super.setBorder(b);
}
}
}
/**
* A subclass of TextPaneComboBoxEditor that implements UIResource.
* TextPaneComboBoxEditor doesn't implement UIResource
* directly so that applications can safely override the
* cellRenderer property with TextPaneListCellRenderer subclasses.
* <p>
* <strong>Warning:</strong>
* Serialized objects of this class will not be compatible with
* future Swing releases. The current serialization support is
* appropriate for short term storage or RMI between applications running
* the same version of Swing. As of 1.4, support for long term storage
* of all JavaBeans™
* has been added to the <code>java.beans</code> package.
* Please see {@link java.beans.XMLEncoder}.
*/
public static class UIResource extends TextPaneComboBoxEditor
implements javax.swing.plaf.UIResource {
}
static class WrappedActionListener extends AbstractAction
{
private ActionListener listener;
public WrappedActionListener(ActionListener listener)
{
this.listener = listener;
}
@Override
public void actionPerformed(ActionEvent e)
{
listener.actionPerformed(e);
}
}
}
All you need in your current code is:
comboBox.setEditor( new TextPaneComboBoxEditor() );
来源：https://stackoverflow.com/questions/31786422/alignment-resets-when-using-seteditable-for-a-jcombobox