设置为NSTextField的值被忽略

Question

I have a class RandomGenerator:

// RandomGenerator.h
#import <Foundation/Foundation.h>
@interface RandomGenerator : NSObject 
{
    @private
    IBOutlet NSTextField* textField;
    unsigned int number;
}
@end

//RandomGenerator.m
#import "RandomGenerator.h"
@implementation RandomGenerator

- (id)init
{
    self = [super init];
    if (self) 
    {
        textField=[[NSTextField alloc]init];
        [textField setStringValue:@"Insert a number between 1 and 100"];
        srand((unsigned int)time(NULL));
    }
    return self;
}
- (void)dealloc
{
    [super dealloc];
}
@end

That when constructed it sets automatically the value of the NSTextField. I allocate a RandomGenerator object from the file GuessTheNumberAppDelegate.m :

#import "GuessTheNumberAppDelegate.h"
#import "RandomGenerator.h"
@implementation GuessTheNumberAppDelegate
@synthesize window;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    NSAutoreleasePool* pool=[[NSAutoreleasePool alloc]init];
    RandomGenerator* random=[[RandomGenerator alloc]init];
    [pool drain];
}
@end

And I have made connections in interface builder:

But the content of the NSTextField is not changed, it appears the same, why this?

Answer 1

In -[RandomGenerator init] , you're creating a new text field object that has no relation to the text field that's already in your xib file, and pointing the outlet at that new object. The objects in the xib are real, actual objects that are allocated for you by the loading mechanism. You don't need textField = [[NSTextField alloc] init]; ,* nor do you need RandomGenerator* random=[[RandomGenerator alloc]init]; . Both of those objects already exist in your xib.

You do need to change a few things, however. First, if you want your application delegate to be able to access the RandomGenerator , you'll need to give it an outlet and connect it: IBOutlet RandomGenerator * generator; . Second, you will need to move [textField setStringValue:@"Insert a number between 1 and 100"]; out of -[RandomGenerator init] . Due to the way nib loading works, the generator's init method will be called before the IBOutlet to the text field is hooked up, and possibly before the text field is even created.

I'm pretty sure that if you add:

- (void)awakeFromNib {
    [textField setStringValue:@"Insert a number between 1 and 100"];
}

to RandomGenerator , that will do the trick. Once the nib has been loaded and all the objects in it are recreated, awakeFromNib should be sent to all those objects.

---

*and that's not the correct initializer for an NSTextField anyways

Answer 2

I agree with Josh, especially on the awakeFromNib part. Below are a couple of additional notes/tests, I coded this up just to check it out. Below are the RandomGenerator files but simplified to illustrate what I thought your question was about:

//  RandomGenerator.h
#import <Foundation/Foundation.h>
@interface RandomGenerator : NSObject {
    IBOutlet NSTextField *textField;
}
@end
--------------
//  RandomGenerator.m
#import "RandomGenerator.h"
@implementation RandomGenerator
- (void)awakeFromNib {
    [textField setStringValue:@"Insert a number between 1 and 100"];
}
@end

And then the AppDelegate files:

//  GuessTheNumberAppDelegate.h
#import <Cocoa/Cocoa.h>
@interface GuessTheNumberAppDelegate : NSObject <NSApplicationDelegate> 
@property (assign) IBOutlet NSWindow *window;
@end
--------------
//  GuessTheNumberAppDelegate.m
#import "GuessTheNumberAppDelegate.h"
#import "RandomGenerator.h"
@implementation GuessTheNumberAppDelegate
@synthesize window = _window;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    RandomGenerator *random = [[RandomGenerator alloc] init];
    NSLog(@"%@",random);
}
@end

Building and running the project I get what you might expect:

with

Note that I didn't need to connect the RandomGenerator as an IBOutlet, I simply made sure its header was included in the GuessTheNumberAppDelegate.h file. But keep in mind that Josh may have something more general in mind, so you may still need to do that.

Hope this helps!