JTextField:如何限制字符数? [英] JTextField: How to limit the number of characters?

问题描述

请查看以下代码.

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();
    }
}

在这里，我试图将字符数限制为5.好，当达到5时，它将停止插入更多字符，但是在这种情况下，它也不允许删除插入的字符，替换或任何事物.如何解决这个问题?

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?

推荐答案

只需更改您当前的删除方法:

simply change your current remove method:

 @Override  
 public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException 
 {  

     fb.insertString(offset, "", null);
 } 

为此:

 @Override  
 public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException 
 {  
     fb.remove(offset, length);
 }

它现在应该可以工作了.

it should now work.

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