change the size of JTextField on KeyPress

Question

I have to extend the size of JTextField on KeyPressed event as user enter the text in textfield.please give me some idea how to achieve this?

thanks in advance

Answer 1

Okay, jumping for it :-)

Let's assume the question is

How to adjust a JTextField's width to always fit its content width?

Usual collaborators

• a LayoutManager which sizes its children at their pref size, f.i. FlowLayout
• JTextField reports its pref size fitted to content
• auto-magical resize expected

Quick example:

JTextField field = new JTextField("something");
JComponent parent = new JPanel(); // has FlowLayout by default
parent.add(field);
frame.add(parent);
// just to ensure it's bigger 
frame.setSize(400, 400);

type ... and nothing happens: size remains at initial size. That's surprise: for some reason, the field's auto-validation simply doesnt't happen. In fact, a manual revalidate of the field on receiving a change notification (Note: the only correct listener type here is a DocumentListener) doesn't change the field as well:

final JTextField field = new JTextField("something");
DocumentListener l = new DocumentListener() {

    private void updateField(JTextField field)
        // has no effect
        field.revalidate();
    }


    @Override
    public void removeUpdate(DocumentEvent e) {
        updateField(field);
    }

    @Override
    public void insertUpdate(DocumentEvent e) {
        updateField(field);
    }

    @Override
    public void changedUpdate(DocumentEvent e) {
   }
};

field.getDocument().addDocumentListener(l);
JComponent parent = new JPanel(); // has FlowLayout by default
parent.add(field);
frame.add(parent);
// just to ensure it's bigger 
frame.setSize(400, 400);

@Gagandeep Bali found out that it's the parent that needs to be revalidated:

private void updateField(JTextField field) {
    field.getParent().revalidate();
}

Unexpected, so the next question is the notorious why? Here: why doesn't the invalidate bubble up the container hierarchy until it finds a validateRoot? The answer is in the api doc:

Calls to revalidate that come from within the textfield itself will be handled by validating the textfield, unless the textfield is contained within a JViewport, in which case this returns false.

Or in other words: it's not bubbled up because the field itself is a validateRoot. Which leaves the other option to override and unconditionally return false:

JTextField field = new JTextField("something") {

    @Override
    public boolean isValidateRoot() {
        return false;
    }
};
JComponent parent = new JPanel(); // has FlowLayout by default
parent.add(field);
frame.add(parent);
// just to ensure it's bigger 
frame.setSize(400, 400);

The price to pay for this, is that the scrolling doesn't work - which isn't a big deal in this context, as the text always fits into the field. Or implement slightly more intelligent, and return true if the actual width is less than the pref.