如何使JTextArea的末尾可编辑
问题描述:
有没有办法让JTextArea的末尾可编辑,并使已经打印到它的任何内容都不可编辑?如何使JTextArea的末尾可编辑
我的意思是,如果我已经写了“Hello World”例如一个JTextArea,我怎么能让它使得用户可以在“Hello World”之后键入任何他们想要的内容,但是他们之前不能输入或删除已经打印的文本?
下面是一个小程序,以证明我的烦恼......
public class Test {
public static void main(String[] args) {
//Here I create a simple JFrame with JTextArea
JTextArea textArea = new JTextArea();
JFrame frame = new JFrame();
JFrame.setDefaultLookAndFeelDecorated(true);
frame.setSize(250, 250);
textArea.setEditable(true);
textArea.setVisible(true);
frame.add(textArea);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
/*Here I print "Hello World" onto the text area.. after the ">>" I want the
the user to be able to type whatever they want.. however I don't want them
to be able to edit the "Hello World"*/
textArea.append("Hello World\n>>");
textArea.setCaretPosition(textArea.getDocument().getLength());
}
}
在用户能够进入任何他们想要的文字..的例子就是我想要的。但是他们也能编辑我使用append打印的文本..我不想要..
我该如何解决这个问题?
答
是的,一个DocumentFilter将工作。创建一个只允许在文档结尾添加文本的情况 - 即偏移量等于文档长度。也完全禁用删除方法。事情是这样:
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;
public class MyFilter extends DocumentFilter {
@Override
public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr)
throws BadLocationException {
// only insert text if at the end of the document
// if offset == document length
if (offset == fb.getDocument().getLength()) {
super.insertString(fb, offset, string, attr);
}
}
@Override
public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs)
throws BadLocationException {
// only replace text if at the end of the document
// if offset == document length
if (offset == fb.getDocument().getLength()) {
super.replace(fb, offset, length, text, attrs);
}
}
@Override
public void remove(FilterBypass fb, int offset, int length) throws BadLocationException {
// do nothing. Totally inactivate this
}
}
你可以测试它像这样:
import javax.swing.*;
import javax.swing.text.PlainDocument;
@SuppressWarnings("serial")
public class LimitedTextArea extends JPanel {
private JTextArea textArea = new JTextArea(15, 50);
public LimitedTextArea() {
// get textArea's Document and cast to PlainDocument:
PlainDocument document = (PlainDocument) textArea.getDocument();
// set the document's filter with "MyFilter"
document.setDocumentFilter(new MyFilter());
textArea.setLineWrap(true);
textArea.setWrapStyleWord(true);
JScrollPane scrollPane = new JScrollPane(textArea);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
add(scrollPane);
}
private static void createAndShowGui() {
LimitedTextArea mainPanel = new LimitedTextArea();
JFrame frame = new JFrame("LimitedTextArea");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}
答
你也可以使用一个NavigationFilter
:
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class NavigationFilterPrefix extends NavigationFilter
{
private int prefixLength;
private Action deletePrevious;
public NavigationFilterPrefix(int prefixLength, JTextComponent component)
{
this.prefixLength = prefixLength;
deletePrevious = component.getActionMap().get("delete-previous");
component.getActionMap().put("delete-previous", new BackspaceAction());
component.setCaretPosition(prefixLength);
}
@Override
public void setDot(NavigationFilter.FilterBypass fb, int dot, Position.Bias bias)
{
fb.setDot(Math.max(dot, prefixLength), bias);
}
@Override
public void moveDot(NavigationFilter.FilterBypass fb, int dot, Position.Bias bias)
{
fb.moveDot(Math.max(dot, prefixLength), bias);
}
class BackspaceAction extends AbstractAction
{
@Override
public void actionPerformed(ActionEvent e)
{
JTextComponent component = (JTextComponent)e.getSource();
if (component.getCaretPosition() > prefixLength)
{
deletePrevious.actionPerformed(null);
}
}
}
private static void createAndShowUI()
{
JTextField textField = new JTextField("Prefix_", 20);
textField.setNavigationFilter(new NavigationFilterPrefix(7, textField));
JFrame frame = new JFrame("Navigation Filter Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(textField);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
createAndShowUI();
}
});
}
}
这将允许用户编辑文本,他们添加到文本字段。
这将阻止选择固定文本。
要了解更多高级功能,请查看Protected Document,它允许您保护文档的多个区域不被更改。
DocumentFilter可能工作。我会试验一下。 –
也演示了[这里](https://*.com/questions/15017148/jtextarea-as-io-console/15025085#15025085);) – MadProgrammer