限制 jtextfield 或区域中的字符输入

Question

我正在尝试限制多个 jtextfield 上的字符输入。这两个字段有不同的字符限制，同时它们不能接受空白作为他们的第一个字符......例如，第一个字段只有 5 个字符限制，然后第二个字段有 10 个字符限制..我被困在这个问题上这是我正在使用的代码：

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

 public class Restriction {

    public Restriction() {
        initComponents();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Restriction();
            }
        });
    }

    private void initComponents() {
        GridBagConstraints Cons = new GridBagConstraints();
        JFrame frame = new JFrame();
        JPanel panel = new JPanel(new GridBagLayout());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JTextField jtf = new JTextField(20);
        JTextField jtf2 = new JTextField(20);
        //add filter to document
        ((AbstractDocument) jtf.getDocument()).setDocumentFilter(new MyDocumentFilter());
        MyDocumentFilter.charLimit(5);
        ((AbstractDocument) jtf2.getDocument()).setDocumentFilter(new MyDocumentFilter());
        MyDocumentFilter.charLimit(10);
        Cons.gridy = 0;
        panel.add(jtf, Cons);
        Cons.gridy = 1;
        panel.add(jtf2,Cons);  
        frame.add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}

class MyDocumentFilter extends DocumentFilter {

    static int Limit;

    public static void charLimit(int Limitation){
        Limit = Limitation;
    }

    @Override
    public void replace(FilterBypass fb, int i, int i1, String string, AttributeSet as) throws BadLocationException {
        //we want standard behavior if we are not placing space at start of JTextField
        //or if we are placing text at start of JTextField but first character is not whitespace
        if ( i!=0 && i< Limit || ( i==0 && !Character.isWhitespace(string.charAt(0)) ) ){
            super.replace(fb, i, i1, string, as);
        }else{
            System.out.println("no spaces allowed");
        }
    }

    @Override
    public void remove(FilterBypass fb, int i, int i1) throws BadLocationException {
        super.remove(fb, i, i1);
    }

    @Override
    public void insertString(FilterBypass fb, int i, String string, AttributeSet as) throws BadLocationException {
        super.insertString(fb, i, string, as);

    }
}

Answer 1

我会使用javax.swing.text.Document

您可以像这样启动它：

 public static Document createTextDocument(int maxLength){
        return new TextDocument(maxLength);
    }

...

Document document = createTextDocument(5); // limit to 5 chars
textField1.setDocument(document);

document = createTextDocument(10); // limit to 10 chars
textField2.setDocument(document);

这里是自定义TextDocument 类：

public class TextDocument extends PlainDocument{


    private static final long serialVersionUID = 1L;
    private int maxLength = Integer.MAX_VALUE;

    TextDocument(){}
    TextDocument(int maxlength){this.maxLength=maxlength;}

     public void setMaxLength(int maxLength) {
            if (maxLength < 0)
                throw new IllegalArgumentException("maxLength<0");
            this.maxLength = maxLength;
        }

     public void insertString(int offset, String str, AttributeSet attr)
     throws BadLocationException {
         if (validateLength(offset, str) == false)
                return;

            super.insertString(offset, str, attr);
     }

     private boolean validateLength(int offset, String toAdd) {
            String str_temp;
            //String str_text = "";
            String str1 = "";
            String str2 = "";
            try {
                str1 = getText(0, offset);
                str2 = getText(offset, getLength() - offset);
            } catch (Exception e) {
                e.printStackTrace();
            }

            str_temp = str1 + toAdd + str2;
            if (maxLength < str_temp.length()) {
                beep();
                return false;
            } else
                return true;

        }

        private void beep() {
            java.awt.Toolkit.getDefaultToolkit().beep();
        }
}

希望对你有帮助

Answer 2

您可以通过覆盖每个 JTextField 的 keyTyped 事件来避免使用 Document 的复杂性：

txtGuess = new JTextField();
txtGuess.addKeyListener(new KeyAdapter() {
    public void keyTyped(KeyEvent e) { 
        if (txtGuess.getText().length() >= 3 ) // limit textfield to 3 characters
            e.consume(); 
    }  
});

这会将猜谜游戏文本字段中的字符数限制为 3 个字符，方法是覆盖 keyTyped 事件并检查文本字段是否已经有 3 个字符 - 如果是，您正在“消耗”键事件（e ) 这样它就不会像平常一样被处理。

希望对你有帮助。