Java Reference
In-Depth Information
The
buttonPane
object will have a
FlowLayout
manager by default, so this will take care of
positioning the buttons. We add the button pane to the dialog content pane using
BorderLayout.SOUTH
to place it at the bottom of the window. Because creating each button involves
several steps, we are using a helper method
createButton()
that only requires the button label as an
argument. Note that we store each button reference in a variable, so we will need to add these as
members of the
FontDialog
class:
private JButton ok; // OK button
private JButton cancel; // Cancel button
We will use these references in the listeners for the button, as we will see in a moment.
We can code the
createButton()
method as a member of the
FontDialog
class as follows:
JButton createButton(String label) {
JButton button = new JButton(label); // Create the button
button.setPreferredSize(new Dimension(80,20)); // Set the size
button.addActionListener(this); // Listener is the dialog
return button; // Return the button
}
We set the preferred size of the button here to ensure the buttons are all the same size. Without this call,
each button would be sized to fit its label so it would look a bit untidy. The listener is the
FontDialog
class, so the
FontDialog
must implement the
ActionListener
interface, which implies an
actionPerformed()
method:
class FontDialog extends JDialog
implements Constants, ActionListener { // For buttons etc.
// Constructor definition...
// createButton() definition...
public void actionPerformed(ActionEvent e) {
Object source = e.getSource(); // Get the source of the event
if(source == ok) { // Is it the OK button?
((SketchFrame)getOwner()).setCurrentFont(font); // Set the selected font
setVisible(false); // Hide the dialog
}
else if(source == cancel) // If it is the Cancel button
setVisible(false); // just hide the dialog
}
// Plus the rest of the class definition...
}
The
getSource()
member of the
ActionEvent
object,
e
, returns a reference to the object that
originated the event, so we can use this to determine which button the method is being called for. We
just compare the
source
object (which is holding the reference to the object to which the event applies)
to each button object in turn. If it is the
OK
button, we call the
setCurrentFont()
method in the
SketchFrame
object that is the parent for this dialog to set the font. If it is the
Cancel
button we just
hide the dialog so Sketcher can continue. Of course we must add the definition of
setCurrentFont()
to the
SketchFrame
class. The code for this will be:
