Objective-C：設置傳遞指針爲零

Question

我有一個問題，設置一個傳遞的指針爲零。當我通過GDB運行下面的代碼時，我發現傳入的變量「string」在被調用的函數中本地設置爲nil，但在調用的範圍內它仍然指向原始的內存地址。我想解決這個問題，將涉及的參考和值訪問運營商的組合，我只是不夠好，在基本面推測這一個:)

#import "AppDelegate.h" 


@interface AppDelegate() 

+(void)releaseAndNullify:(id)input; 

@end 


@implementation AppDelegate 
@synthesize window; 


-(void)applicationDidFinishLaunching:(NSNotification *)aNotification 
{ 
NSString *string = [NSString string]; 
[AppDelegate releaseAndNullify:string]; 
} 


+(void)releaseAndNullify:(id)input 
{ 
if (input) 
{ 
    [input release]; 
    input = nil; 
} 
} 


-(void)dealloc 
{ 
[window release]; 

[super dealloc]; 
} 


@end 

Answer 1

這是我從另一篇文章中的修補程序：

#import "AppDelegate.h" 


@interface AppDelegate() 

+(void)releaseAndNullify:(NSString **)input; 

@end 


@implementation AppDelegate 
@synthesize window; 


-(void)applicationDidFinishLaunching:(NSNotification *)aNotification 
{ 
NSString *string = [NSString string]; 
[AppDelegate releaseAndNullify:&string]; 
} 


+(void)releaseAndNullify:(NSString **)input 
{ 
if (!*input) return; 

[*input release]; 
*input = nil; 
} 


-(void)dealloc 
{ 
[window release]; 

[super dealloc]; 
} 


@end 

Answer 2

Objective-C的參數是按值傳遞，而不是參考。