Java: Prevent opening duplicate dialogs

[iczman]

I'm working on a java project that it has a menu where you can click File > Login to pop out a dialog for user to enter their login info.

My problem is, when the login dialog is present, user and focus back to the main JFrame and select File > Login to pop out another dialog. I'm searching for a way to prevent this from happening. So far I thought about two solutions but I don't know which is the best way to go about solving this kind of issue:

Solution 1: In my customzied JFrame class, declare a boolean that holds the visibility of the login dialog. Whenever the user goes File > Login, it will first check to see if it's already visible or not, then open the dialog if it's not already opened.

Solution 2: Prevent user to set focus back to the main JFrame when the dialog box is opened.

If you were me, how would you approach this problem? And which one is more effective or a common practice?

[kjordan2001]

Sounds like you're creating it multiple times. Only create it once and use setVisible to toggle the visibility.

You can make it modal as well if you're requiring that they need to fill that in before doing anything in the other frame.

[Menge]

erm... make the dialog modal. that should fix it.

if you don't want a modal dialog, you can have a private static bool isOpened=false;

that when it's opened it sets that to true and sets back to false when its closed. and on the creator of that dialog it just fails if the isOpened is true :p

i'd _really_ recommend the modal approach :p

[kjordan2001]

  Menge said:

erm... make the dialog modal. that should fix it.

if you don't want a modal dialog, you can have a private static bool isOpened=false;

that when it's opened it sets that to true and sets back to false when its closed. and on the creator of that dialog it just fails if the isOpened is true :p

i'd _really_ recommend the modal approach :p

That's not necessary. Create just one instance of it (global in your class that you're showing it in) and just have it so it hides when it closes:

myDialog.setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE);

which is the default action.

And to make it visible:

myDialog.setVisible(true);

And if you're having to do some custom listener stuff for buttons and stuff and want to hide it after the user clicks it, put:

myDialog.setVisible(false);

in your action listener.

Edited February 19, 2006 by kjordan2001

[Winston]

  kjordan2001 said:

That's not necessary. Create just one instance of it (global in your class that you're showing it in) and just have it so it hides when it closes:

myDialog.setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE);

which is the default action.

And to make it visible:

myDialog.setVisible(true);

And if you're having to do some custom listener stuff for buttons and stuff and want to hide it after the user clicks it, put:

myDialog.setVisible(false);

in your action listener.

But if you do that, if people type info in the fields. You'll have to manually reset the fields, otherwise the next time the dialog shows, the info from the previous time the dialog was shown, will still be present.

[kjordan2001]

  Winston said:

But if you do that, if people type info in the fields. You'll have to manually reset the fields, otherwise the next time the dialog shows, the info from the previous time the dialog was shown, will still be present.

Just have it reset them in the submit action listener. Either way you'll have to do some work, question is which kind. Resetting or setting a variable.

[_kane81]

The best solution is to make the dialog a singleton ... ie only one instance can ever be created. Its called the singleton pattern. Its design pattern, google it

heres a quick example

public class MyFrame extends JFrame {

   public static MyFrame instance;

   private MyFrame() {
	 super(); 
   }

   public static MyFrame getInstance() {
	  if (instance = null)
		  instance = new MyFrame();
	  return instance;
   }

   main() {

	 MyFrame.getInstance().setVisbile(true);
	 ... or
	 MyFrame frame = MyFrame.getInstance();
	 frame.setVisible(true);
   }

   public void cleanup() {
	 instance = null;
  }
}

you will only ever get this one dialog only one instance can every be created. Note: you will need to free the instance yourself as the JVM will not clean it up.

[iczman]

Thanks guys. I decided to make the JDialog modal, as it's the easiest way for me to solve this problem.

[_kane81]

^

dont forget to think of the singleton pattern, if you create a dialog that is more complex than what the JDialog can offer