How to instantiate a control in code instead of using Interface Builder ?

Question

I really appreciate the combination of the interface builder and Xcode altogether.
However when I am learning QT, I realize I had been pampered by Apple's Design to a certain extend as I only need to create say a NSLabel instance and use Interface Builder to do the linking and never have to worry about instantiating the Object myself.
But I'm curious, what is the way to instantiate a new hmmm say...NSLabel in the code ?
NSLabel* label = new NSLabel();
Then what ?
What you are seeing here is how QT did it, could anyone create an equivalent in ObjC ? No fancy code please, just bare minimum.
#include <QApplication>
#include <QWidget>
#include <QLabel>
int main (int argc, char * argv [ ])
QApplication app(argc, argv); //NSApplication in ObjC
//These two lines merely created a window and set the title bar text.
QWidget* window = new QWidget();
window->setWindowTitle("Hello World");
QLabel* label = new QLabel(window);//Create a label and inform the it belongs to window.
label->setText("Hello World");
window->show();
return app.exec();
Message was edited by: Bracer Jack

Answer 1

Hi Jack -
I think my best answer will be something of a disappointment, because I don't know how to show a one-to-one correspondence between the code you're working with and a Cocoa program. The main function of a Cocoa GUI program for OS X will look something like this:
#import <Cocoa/Cocoa.h>
int main(int argc, char *argv[])
return NSApplicationMain(argc, (const char **) argv);
As you commented, we could draw a correspondence between the first statements, but after that the functionality of the Cocoa program is going to be spread out in a way that makes for a rather tedious comparison. The only way I know to answer your question in less than 5000 words, is to skip ahead to one of several points in the startup sequence where the programmer can intervene with custom code.
For example, a common way to get control would be to program a custom controller class and add an object of that class to the main nib file which is loaded during the startup sequence. By making a connection to the Application object in that nib file, the custom object could be made the delegate of the Application object, and if we then added a method named applicationDidFinishLaunching, our code would run as soon as the application's run loop was started.
Now I finally have enough context to directly answer your question, so here is the code to create a label and add it to the key window at launch time:
// MyAppController.m
#import "AppController.h"
@implementation AppController
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
NSLog(@"applicationDidFinishLaunching");
NSRect frameRect = NSMakeRect(150, 300, 150, 30);
NSTextField *label = [[NSTextField alloc] initWithFrame:frameRect];
[label setEditable:NO];
[label setStringValue:@"Hello World!"];
[label setFont:[NSFont labelFontOfSize:20]];
[label setAlignment:NSCenterTextAlignment];
NSView *contentView = [self.window contentView];
[contentView addSubview:label];
@end
If I needed to develop a worst case scenario for this thread, the next question would be, "Ok sure, but your code still needs a nib to start up. I want to see a Cocoa GUI program that doesn't require any nib".
It turns out that it's quite easy to build a simple iPhone app without any nib, but it's considerably more difficult for an OS X app. If anyone wants to see my nib-less iPhone code, I'll be happy to post it (I think I did post it here once before, and the response was underwhelming). But I've never attempted the much more difficult nib-less OS X app. Just in case you really want to go there, here's a blog that goes into the details: [http://lapcatsoftware.com/blog/2007/07/10/working-without-a-nib-part-5-open-re cent-menu>.
Hope some of the above is helpful!
- Ray