NSString works with one method but not the other - objective-c

Question

I have two different methods of trying to grab a variable from another class. The first one, which I would prefer using doesn't work - The second one, which I don't prefer does. Could someone please explain why?
AppDelegate.h
#import <Cocoa/Cocoa.h>
#interface AppDelegate : NSObject <NSApplicationDelegate> {
NSString *someString;
}
#property (assign) IBOutlet NSWindow *window;
#property (retain, nonatomic) NSString *someString;
- (void)manualSetVariable;
#end
AppDelegate.m
#import "AppDelegate.h"
#import "GrabFromAppDelegate.h"
#implementation AppDelegate
#synthesize someString;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
someString = #"The Variable";
NSLog(#"In AppDelegate (1): %#",someString);
GrabFromAppDelegate *getThis = [[GrabFromAppDelegate alloc] init];
getThis.varSet = someString;
}
- (void)manualSetVariable { // THIS METHOD WORKS (2)
someString = #"The Variable";
NSLog(#"In AppDelegate(2): %#",someString);
}
#end
GrabFromAppDelegate.h
#import <Foundation/Foundation.h>
#interface GrabFromAppDelegate : NSObject {
NSString *varSet;
IBOutlet NSTextField *variable;
}
#property(retain, nonatomic) NSString *varSet;
- (IBAction)showVariable:(id)sender;
- (IBAction)manuallyGrabVariable:(id)sender;
#end
GrabFromAppDelegate.m
#import "GrabFromAppDelegate.h"
#import "AppDelegate.h"
#implementation GrabFromAppDelegate
#synthesize varSet;
- (IBAction)showVariable:(id)sender {
if (varSet != NULL) {
[variable setStringValue:[NSString stringWithString:varSet]];
NSLog(#"Got String Using (1): %#",varSet);
}
}
- (IBAction)manuallyGrabVariable:(id)sender { // THIS METHOD WORKS (2)
AppDelegate *getString = [[AppDelegate alloc] init];
[getString manualSetVariable];
if ([getString someString] != NULL) {
[variable setStringValue:[NSString stringWithString:[getString someString]]];
NSLog(#"Got String Using (2): %#",[getString someString]);
}
}
#end

Answer 1

This is horribly wrong:
AppDelegate *getString = [[AppDelegate alloc] init];
That allocates an AppDelegate instance, but it's not [[NSApplication sharedApplication] delegate], so the getString instance will never execute the applicationDidFinishLaunching method and your someString iVar will never get set. If you'd set someString within an init function, [[AppDelegate alloc] init] would, of course, call init. But since getString isn't attached to an NSApplication instance, there's nothing delegating the applicationDidFinishLaunching method to it.
If you want to get a pointer to the application delegate, you can do:
AppDelegate *getString = [[NSApplication sharedApplication] delegate];
or, for brevity's sake:
AppDelegate *getString = [NSApp delegate];

Answer 2

In second method you are calling method from app delegate and value is set at that time in someString variable and you get response. However if you are setting value for a varibale in appDelegate using an instance the set value will passed to that particular instance of controller class not to all instances. Hence either you create a shared instance of that variable or call that particular instance
to get the value somestring by showVariable method.