文档过滤器在Java中不起作用？

问题描述

在文本字段中超过10个字符na，它必须显示错误。对于我使用的文档过滤器：

In text field more than 10 characters na, it has to show an error. For that i used document filter:

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。如何使用文档过滤器？

So this is my document filter coding. I registered the textfield through document filter. But nothing has happening here. How to use document filter?

DocumentSizeAndUppercaseFilter类，其中包含错误消息。

DocumentSizeAndUppercaseFilter class which has the error msg.

推荐答案

没有看到 DocumentSizeAndUppercaseFilter 的代码，我怀疑你没有实现（/覆盖） 方法：

Without seeing the code for DocumentSizeAndUppercaseFilter I would suspect that you havn't implemented (/override) the DocumentFilter's replace method:

@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：

---

Screenshot from the code below:

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 ：

Example 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);
}

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