文档过滤器在Java中不起作用？

Question

在文本字段中超过10个字符na,它必须显示错误.为此我用过文档过滤器:

JTextField field = (JTextField) txtFld;
AbstractDocument document = (AbstractDocument) field.getDocument();
document.setDocumentFilter(new DocumentSizeAndUppercaseFilter(10));

所以这是我的文档过滤器编码.我通过文档过滤器注册了文本字段.但这里什么也没发生.如何使用文件过滤器？

具有错误消息的DocumentSizeAndUppercaseFilter类.

Answer 1

没有看到代码,DocumentSizeAndUppercaseFilter我会怀疑你没有实现(/覆盖)DocumentFilter的replace方法:

@Override
public void replace(DocumentFilter.FilterBypass fb, int offset,
                    int length, String text, AttributeSet attrs)
        throws BadLocationException {

    ....
}

以下代码的屏幕截图:

示例实现DocumentSizeAndUppercaseFilter:

static class DocumentSizeAndUppercaseFilter extends DocumentFilter {

    private final int max;

    public DocumentSizeAndUppercaseFilter(int max) {
        this.max = max;
    }

    @Override
    public void insertString(DocumentFilter.FilterBypass fb, int offset,
                             String text, AttributeSet attr) 
            throws BadLocationException {
        if (fb.getDocument().getLength() + text.length() < max)
            super.insertString(fb, offset, text.toUpperCase(), attr);
        else 
            showError();
    }

    @Override
    public void replace(DocumentFilter.FilterBypass fb, int offset,
                        int length, String text, AttributeSet attrs)
            throws BadLocationException {
        int documentLength = fb.getDocument().getLength();
        if (documentLength - length + text.length() < max)
            super.replace(fb, offset, length, text.toUpperCase(), attrs);
        else 
            showError();
    }

    private void showError() {
        JOptionPane.showMessageDialog(null, "Too many characters entered");
    }
}

示例main:

public static void main(String[] args) {

    JTextField firstName = new JTextField();
    AbstractDocument d = (AbstractDocument) firstName.getDocument();
    d.setDocumentFilter(new DocumentSizeAndUppercaseFilter(10));

    JFrame frame = new JFrame("Test");
    frame.add(firstName);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(200, 60);
    frame.setVisible(true);
}