Re: File's Owner

Sun, 25 May 2008 03:21:18 -0700 


On May 25, 2008, at 12:15 AM, Johnny Lundy wrote:


And, if I don't understand something, I will ask why.


Here are some suggestions as to how you might pose your questions:
        <http://www.catb.org/~esr/faqs/smart-questions.html>
This is not magic - there is actual computer code behind that File's Owner concept, and it is deterministic, not vague, not abstract, not a philosophical enigma, not random, not ambiguous. If I had the source code I could see what it does.
But that's where you're leading yourself astray -- there isn't any source code to see. The nib file is an object graph with a hole in it. The File's Owner is the hole -- the one thing that *isn't* created in the nib. 



This is a *very rough* approximation:


@interface MyNibManager : NSObject
{
}
- (void)createNibForWindowWithButton:(NSString *)fileName;
- (void)loadNibForWindowWithButton:(NSString *fileName) withOwner: (id)filesOwner; 

@end


@implementation MyNibManager


- (void)createNibForWindowWithButton:(NSString *)fileName {

        NSRect contentRect = NSMakeRect(100, 200, 400, 300);
NSWindow *aWindow = [[NSWindow alloc] initWithContentRect:contentRect styleMask:NSTitledWindowMask backing:NSBackingStoreBuffered defer:NO]; 

        NSRect buttonFrame = NSMakeRect(10, 20, 80, 20);
        NSButton *aButton = [[NSButton alloc] initWithFrame:buttonFrame];
        [aButton setButtonType:NSMomentaryLightButton];
        [aButton setTitle:@"Push Me"];
        [aButton setAction:@selector(myAction:)];
        [aButton setTarget:(id)-1]; // pretend kludge to represent File's Owner
        // Notice that there's no code for File's Owner itself

        [[aWindow contentView] addSubview:aButton];


        NSArray *tloArray = [NSArray arrayWithObject:aWindow];

        NSDictionary *nib = [NSDictionary dictionaryWithObject:tloArray
                                forKey:@"TopLevelObjects"];

        [NSKeyedArchiver archiveRootObject:nib toFile:fileName]
}
- (void)loadNibForWindowWithButton:(NSString *fileName) withOwner: (id)filesOwner {
NSDictionary *nib = [NSKeyedUnarchiver unarchiveObjectWithFile:fileName]; 

        NSArray *tloArray = [nib objectForKey:@"TopLevelObjects"];

        [filesOwner setWindow:[tloArray objectAtIndex:0]];
NSTextField *aButton = [[[window contentView] subViews] objectAtIndex: 0]; 
        [filesOwner setButton:aButton];

        if ([button target] == (id)-1) {
                [button setTarget:filesOwner];
        }
}

                        
@end





@interface MyFilesOwner : NSObject
{
        IBOutlet NSWindow *window;
        IBOutlet NSButton *button;
}

@property NSWindow *window;
@property NSButton *button;

- (IBAction)myAction:sender;

@end



@implementation MyFilesOwner

@synthesize window, button;


- (IBAction)myAction:sender {
        NSLog(@"Button pressed");
}

- (void)dealloc {
        [window release];
        [button release];
        [super dealloc];
}

@end





int main(int argc, char *argv[])
{
NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:@"MyInterface.mnib"]; 

        MyNibManager *myNibManager = [[MyNibManager alloc] init];
        [myNibManager createNibForWindowWithButton:fileName];
        
        MyFilesOwner *filesOwner = [[MyFilesOwner alloc] init];
        [myNibManager loadNibForWindowWithButton:fileName ithOwner:filesOwner];

        // ...
}
Despite teaching OB/GYN for 17 years, this is why computer science is always my main interest.
Perhaps it's your background that's causing you the problem. My father was Dr. J. Selwyn Crawford. I persuaded him to buy a Mac in 1986. He somehow failed to understand (a rarity) that when you use a word processor you don't have to put Returns at the end of the line...
I've written firmware before we called it firmware. I have never NOT been able to grasp something until this and bindings. Aaron says lots of people have trouble understanding File's Owner, so I can only conclude that it's the documentation, or lack thereof.
I think this is a fallacious conclusion. There are numerous descriptions of File's Owner, and people typically read many of them. My perspective, after teaching this for some time, is that some people simply have difficulty understanding that it's as easy as it is. It's got to be more complicated... 
It isn't.

Interface Builder is a WYSIWYG object graph editor.
A nib file is an archived object graph.
File's Owner is a place-holder for an object created outside of the nib that is made the "owner" of the object graph when the object graph is unarchived (i.e. when the nib file is loaded). When the nib file is loaded, any connections you made between objects in the object graph and the File's Owner are reestablished using the object set to be the owner (typically in -loadNibNamed:owner:). 


mmalc

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