Question

Consider a JFormattedTextField (or any JTextComponent, really) wherein there is a prefix and a suffix displayed around what is the actual “text” of the field.

For instance, the double 3.5 would be the String (via formatting) “3.50” around which would be the prefix “$ ” and the suffix “”, for a display text of “$ 3.50”.

Clearly, this is simple to do. However, the user is still allowed to select text within the prefix/suffix, so they could conceivably delete part or all of the prefix/suffix. I would prefer the user be restricted such that the prefix/suffix cannot be selected at all (while still part of the text field, so no JLabels). I can almost accomplish this with a CaretListener (or by overriding setCaretPosition/moveCaretPosition), which prevents a C-a from selecting the entire field, and it prevents using the arrow keys to move into the prefix/suffix. However, mouse dragging and shift-arrow keys still allows the selection to move into these restricted areas.

Any ideas?

Answer 1

You can use a NavigationFilter for this.

Here is an example to get you started:

import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;

public class NavigationFilterPrefixWithBackspace extends NavigationFilter
{
    private int prefixLength;
    private Action deletePrevious;

    public NavigationFilterPrefixWithBackspace(int prefixLength, JTextComponent component)
    {
        this.prefixLength = prefixLength;
        deletePrevious = component.getActionMap().get("delete-previous");
        component.getActionMap().put("delete-previous", new BackspaceAction());
        component.setCaretPosition(prefixLength);
    }

    public void setDot(NavigationFilter.FilterBypass fb, int dot, Position.Bias bias)
    {
        fb.setDot(Math.max(dot, prefixLength), bias);
    }

    public void moveDot(NavigationFilter.FilterBypass fb, int dot, Position.Bias bias)
    {
        fb.moveDot(Math.max(dot, prefixLength), bias);
    }

    class BackspaceAction extends AbstractAction
    {
        public void actionPerformed(ActionEvent e)
        {
            JTextComponent component = (JTextComponent)e.getSource();

            if (component.getCaretPosition() > prefixLength)
            {
                deletePrevious.actionPerformed( null );
            }
        }
    }

    public static void main(String args[]) throws Exception {

        JTextField textField = new JTextField("Prefix_", 20);
        textField.setNavigationFilter( new NavigationFilterPrefixWithBackspace(7, textField) );

        JFrame frame = new JFrame("Navigation Filter Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(textField);
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
    }
}

I believe this is a how a JFormattedTextField works. So I’m not sure if you can use this with a formatted text field as is may replace the default behaviour.