带有 invokelater 的 documentlistener 进入无限循环

Question

我有一个带有文本字段的 Jpanel。我正在使用 documentListener 将更改保存为用户在文本字段中键入的内容。用户可以在 1-1000 之间输入，如果他输入任何其他内容，将会弹出错误消息。现在，我正在使用 invokeLater，但如果用户输入 >1000，则会导致无限循环。我该如何解决这个问题。

mMaxLabelLength = new JTextField();
mMaxLabelLength.getDocument().addDocumentListener(this);
@Override
public void changedUpdate(DocumentEvent arg0)
{
}

@Override
public void insertUpdate(DocumentEvent arg0)
{
    saveActions();
    mMaxLabelLength.requestFocus();

}

@Override
public void removeUpdate(DocumentEvent arg0)
{
    saveActions();
    mMaxLabelLength.requestFocus();
}
private boolean saveActions()
{
    // get text
    String strValue = mMaxLabelLength.getText();

    // validate: must be positive integer between 1-1000;
    boolean bSaveIt = true;
    try
    {
        int nValue = Integer.parseInt(strValue);
        if (nValue < 1 || nValue > 1000)
            bSaveIt = false;
    }
    catch (NumberFormatException ne)
    {
        bSaveIt = false;
    }

    // save data to properties if valid
    if (bSaveIt)
    {
        //do something
    }
    else
    {
        // error message
        JOptionPane.showMessageDialog(this, "Please enter an integer value between 1 and 1000.", "Invalid Entry", JOptionPane.INFORMATION_MESSAGE);
                SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                                    int nMaxLabel = getMaxPieLabel();
                mMaxLabelLength.setText(new Integer(nMaxLabel).toString());
            }
        });
        return false;
    }
    setVisible(true);
    return true;
}

Answer 1

修改 Document 的状态或与 UI 交互并不是 DocumentListener 的真正职责范围。

相反，您可能应该使用 DocumentFilter，这将允许您在无效状态提交到 Document 之前捕获无效状态，并使用自定义事件通知来提醒相关方违规行为已经发生，例如...

import java.awt.EventQueue;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class Example {

    public static void main(String[] args) {
        new Example();
    }

    public Example() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            setBorder(new EmptyBorder(20, 20, 20, 20));
            JTextField field = new JTextField(10);
            LimitedRangeDocumentFilter filter = new LimitedRangeDocumentFilter(1, 1000);
            filter.setLimitedRangeDocumentFilterListener(new LimitedRangeDocumentFilterListener() {
                @Override
                public void updateWouldBeInvalid(LimitedRangeDocumentFilter filter, String text) {
                    JOptionPane.showMessageDialog(TestPane.this, 
                            text + " is not within " + filter.getMin() + "-" + filter.getMax() + " range",
                            "Error",
                            JOptionPane.ERROR_MESSAGE);
                }
            });
            ((AbstractDocument)field.getDocument()).setDocumentFilter(filter);
            add(field);
        }

    }

    public interface LimitedRangeDocumentFilterListener {
        public void updateWouldBeInvalid(LimitedRangeDocumentFilter filter, String text);
    }

    public class LimitedRangeDocumentFilter extends DocumentFilter {

        private int min;
        private int max;

        private LimitedRangeDocumentFilterListener listener;

        public LimitedRangeDocumentFilter(int min, int max) {
            this.min = min;
            this.max = max;
        }

        public int getMin() {
            return min;
        }

        public int getMax() {
            return max;
        }

        public void setLimitedRangeDocumentFilterListener(LimitedRangeDocumentFilterListener listener) {
            this.listener = listener;
        }

        @Override
        public void insertString(DocumentFilter.FilterBypass fb, int offset,
                String string, AttributeSet attr)
                throws BadLocationException {

            StringBuilder sb = new StringBuilder(string);
            for (int i = sb.length() - 1; i >= 0; i--) {
                char ch = sb.charAt(i);
                if (!Character.isDigit(ch)) {
                    sb.deleteCharAt(i);
                }
            }

            StringBuilder master = new StringBuilder(fb.getDocument().getText(0, fb.getDocument().getLength()));
            master.insert(offset, sb.toString());
            if (wouldBeValid(master.toString())) {
                super.insertString(fb, offset, sb.toString(), attr);
            } else if (listener != null) {
                listener.updateWouldBeInvalid(this, master.toString());
            }
        }

        @Override
        public void replace(DocumentFilter.FilterBypass fb,
                int offset, int length, String string, AttributeSet attr) throws BadLocationException {
            if (length > 0) {
                fb.remove(offset, length);
            }
            insertString(fb, offset, string, attr);
        }

        protected boolean wouldBeValid(String text) {
            boolean wouldBeValid = false;
            try {
                int value = Integer.parseInt(text);
                if (value >= min && value <= max) {
                    wouldBeValid = true;
                }
            } catch (NumberFormatException exp) {
            }
            return wouldBeValid;
        }
    }

}

有关详细信息，请参阅 Implementing a Document Filter and DocumentFilter Examples

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