problems with creating an NSWindow - objective-c

Question

I am new to Cocoa, and I am just experimenting with creating a window programmatically (without using Interface Builder).
I start a new Cocoa Application in Xcode, then I remove the window from the nib file in Interface Builder to replace it with my own one.
In the main function, I add the code:
NSWindow* myWindow;
myWindow = [[NSWindow alloc] initWithContentRect:NSMakeRect(10,100,400,300)
styleMask:NSTitledWindowMask
backing:NSBackingStoreBuffered
defer:NO];
When I try to build and run the application, I receive the following error message:
Error (1002) creating CGSWindow
Why does this happen??? What is a CGSWindow by the way?
Rainer

Answer 1

You probably don't have a connection to the window server yet. That's NSApplication's job, so try creating the shared application first.
If that doesn't help, I'd just go through with my usual application layout: Create an NSObject subclass for a custom controller, instantiate this from your application delegate's applicationWillFinishLaunching: and release it in applicationWillTerminate:, and have your custom controller's init method create the window. The application object will definitely be running by this point (as main does nothing but call NSApplicationMain, which gets/creates the shared application and tells it to run), so you should definitely have your connection to the window server and so be able to create the window.

Answer 2

Move the code you've written into the following method from your App Delegate implementation file -
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Insert code here to initialize your application
NSWindow* myWindow;
myWindow = [[NSWindow alloc] initWithContentRect:NSMakeRect(10,100,400,300)
styleMask:NSTitledWindowMask
backing:NSBackingStoreBuffered
defer:NO];
}
and it should load your window perfectly.
It's worth noting that it's never safe and is not a good practice to create any UI related objects in your main function.

Answer 3

If you want to display a completely empty window from scratch this is all the code you'll need:
//if you used a template this will be already in the file:
int main(int argc, char *argv[])
{
NSAutoreleasePool *pool = [[NSAutoReleasePool alloc] init];
int retval=UIApplicationMain(argc,argv,nil,#"SimpleWindowAppDelegate");
[pool release];
return retVal;
}
#implementation SimpleWindowAppDelegate : NSObject <UIApplicationDelegate>
-(void) applicationDidFinishLaunching:(UIApplication *)application
{
UIWindow *window=[[UIWindow alloc] initWithFrame:[[UIDevice mainScreen] bounds]];
//You could create views and add them here:
//UIView *myView=[[UIView alloc] initWithFrane:CGRectMake(0,0,50,50)];
//[window addSubView:myView];
//[myView release];
[window makeKeyAndVisible];
}
#end

Answer 4

The only code that you will probably ever want to have in your main() function in a Cocoa application is automatically created for you by XCode (if you are using it).
I suggest that you add the code that you want into your applicationDelegate's -applicationDidFinishLaunching: method
- (void) applicationDidFinishLaunching:(NSNotification *)aNotification {
myWindow = [[NSWindow alloc] initWithContentRect:NSMakeRect(10,100,400,300)
styleMask:NSTitledWindowMask
backing:NSBackingStoreBuffered
defer:NO];;
}