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Getting the application to
quit when the main window closes
The trick here is to create a method that calls
Environment.Exit() to quit the application like any other .NET
The other trick is to notice that Environment.Exit() does not work
when Cocoa objects are alive. But
NSApplication.SharedApplication.Terminate(this) works. I don't know
how to return an error code that way.
Cocoa, and thus MonoMac, uses "delegates" to allow one object to
react when something happens to another object. We will use this
concept to call Terminate() when the main window closes.
A Cocoa object has "outlets", which appear to be pointers to other
objects. I don't know if this is technically the correct
description. It doesn't matter. One of the outlets is the "delegate"
which we will set to the object that contains the method that we
want called when the window is closed. Hence we have to set the main
window's delegate outlet to our object.
We will use the MainWindow class defined in MainWindow.cs as
delegate for the main window. I guess that means we are using an
object as its own delegate or something like that. It will still
To make MainWindow the delegate for the main window and react to the
main window closing follow these steps.
1. Double-click MainWindow.xib to open Xcode.
2. In Xcode, find the main window. It's the big thing that looks
like a window.
Picture 1: The big thing titled "Window" is the main window.
3. Right-click on the title bar of the window to display the
You will see one outlet called "delegate".
Picture 2: One of the "Outlets" is "delegate".
4. Find the "Object Library" and the blue box in it. The blue box is
Picture 3: The blue box is an object.
5. Drag the blue box to the grey thingy with the icons to the left
of the window.
Picture 4: The blue box belongs under the window icon.
6. Make the blue box a "MainWindow" object. Click on the blue box
and change its class to "MainWindow".
Picture 5: Update the class name for the blue box.
7. Press the control key and drag from the window title bar into the
blue box. Then select the "delegate" option in the menu that
Picture 6: The menu that appears when you control-drag.
Our MainWindow object is now the delegate for the main window. This
means it can react to things that happen to the window.
8. Add the following code to MainWindow.cs:
public void WindowWillClose(NSNotification
The [Export ("windowWillClose:")]
statement tells the compiler (presumably the compiler, but maybe
some other utility technically does the being told) that the
following method declaration is the C# equivalent of the Objective-C
method announced. The method can have a different actual name but
should be named similarly enough so that we can identify it easily
enough. I usually just change the first letter to its upper-case
version to conform to C# style.
9. Compile the application, fix all the typos you made, then run it.
Try closing the window. The application will quit.
If not, repeat all the steps told here until it does..
(c) Andrew J. Brehm
Feel free to copy/translate/whatever but keep a pointer to the
original location in case I find one of my many, many mistakes and
update the document.
Zurich, January 22nd 2012