Extended JDialog to pop-up in center of parent frame

Question

I have a JDialog extended, and I want it to pop up in the center of the parent frame when A button is pressed in the frame. The button is in the constructor of the main frame, and uses an anonymous inner class to attach the action listener to the button. I am calling the outter class (MainFrame) with the "this" reference, and I get bogus results. MapParameters is extended from JDialog.
when I instantiate the JDialog with this line "mp = new MapParameters(MainFrame.this,true)" It puts the dialog in the upper left corner of the screen, which is the same results as if I were to use "null" where "MainFame.this" is.
What am I doing wrong?

Answer 1

You have to calculate the locations if you want to center the dialog on the frame. Add this code to either your the MainFrame where you create the dialog or in the JDialog extended class. Make sure the size of the dialog is set (ie it has been laid out if you are using a layout manager or set it using setSize if you are laying out components manually) before this code is executed.
//Center the dialog
Dimension frameSize = frame.getSize();
Dimension dialogSize = dialog.getSize();
if (dialogSize.height > frameSize.height) dialogSize.height = frameSize.height;
if (dialogSize.width > frameSize.width) dialogSize.width = frameSize.width;
dialog.setLocation((frameSize.width - dialogSize.width) / 2, (frameSize.height - dialogSize.height) / 2);