java JTextField：如何限制字符数？
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JTextField: How to limit the number of characters?
提问by Lemon Juice
Please have a look at the following code.
请看下面的代码。
import java.awt.FlowLayout;
import java.awt.GridLayout;
import javax.swing.*;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;
public class Bean extends JFrame
{
private JTextField field1, field2, field3, field4;
private JLabel text;
private JButton ok, cancel;
private JPanel centerPanel,southPanel, textPanel;
private GridLayout grid;
private FlowLayout flow1, flow2;
public Bean()
{
//Declaring instance Variables
field1 = new JTextField(10);
field2 = new JTextField(5);
field3 = new JTextField(5);
field4 = new JTextField(5);
text = new JLabel("Insert Your Numbers Here");
AbstractDocument d = (AbstractDocument) field1.getDocument();
d.setDocumentFilter(new Bean.Field1Listener());
ok = new JButton("OK");
cancel = new JButton("Cancel");
/***********************Creating the main view*************************/
centerPanel = new JPanel();
grid = new GridLayout(2,1,1,1);
//Adding TextFields
textPanel = new JPanel();
flow1 = new FlowLayout(FlowLayout.CENTER);
textPanel.setLayout(flow1);
textPanel.add(field1);
//Adding Buttons
southPanel = new JPanel();
southPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
southPanel.add(ok);
southPanel.add(cancel);
//Creating Center View
centerPanel.setLayout(grid);
centerPanel.add(text);
centerPanel.add(textPanel);
//Gathering everything together
getContentPane().add(centerPanel,"Center");
getContentPane().add(southPanel,"South");
this.setSize(500,200);
this.validate();
this.setVisible(true);
this.setLocationRelativeTo(null);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private class Field1Listener extends DocumentFilter
{
@Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException
{
if(fb.getDocument().getLength()+string.length()>5)
{
return;
}
fb.insertString(offset, string, attr);
}
@Override
public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException
{
fb.insertString(offset, "", null);
}
@Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs)throws BadLocationException
{
if(fb.getDocument().getLength()+text.length()>5)
{
System.out.println("OK");
return;
}
fb.insertString(offset, text, attrs);
}
}
public static void main(String[]args)
{
new Bean();
}
}
In here, I am trying to limit the number of character to 5. OK, it stops inserting anymore characters when it reaches 5, but the case is, it also doesn't allow to delete the inserted characters, replace, or anything. How to correct this issue?
在这里，我试图将字符数限制为 5。好吧，当它达到 5 时它会停止插入更多字符，但情况是，它也不允许删除插入的字符、替换或任何东西。如何纠正这个问题？
回答by Basilio German
simply change your current remove method:
只需更改您当前的删除方法：
@Override
public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException
{
fb.insertString(offset, "", null);
}
for this one:
对于这个：
@Override
public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException
{
fb.remove(offset, length);
}
it should now work.
它现在应该可以工作了。
回答by Hidde
You should make your own class that checks whether you gave more input than the maximum allowed length: See an example on http://www.java2s.com/Tutorial/Java/0240__Swing/LimitJTextFieldinputtoamaximumlength.htm.
您应该创建自己的类来检查是否提供了超过最大允许长度的输入：参见http://www.java2s.com/Tutorial/Java/0240__Swing/LimitJTextFieldinputtoamaximumlength.htm上的示例。
