多級繼承的客觀C [self init]層次

Question

我有繼承類B的類A，並且想實現類似下面的類。但是由於動態類型轉換，init方法獲得了遞歸調用。 有沒有辦法實現這樣的？任何建議？ （無子類中改變「init的名字？

@interface A : NSObject 
@property NSData * data; 
@end 

---

@implementation A 

- (id) init { 
    self = [super init]; 
    /* want to do some default initialization here 
     for this class and all of its subclasses. */ 
    // ... ... 
    return self; 
} 

/* This [self init] get recursed. 
    But how can I force this class and all of its subclass to call [self init] above, 
    not to call the subclass's init method. */ 

- (id) initWithData:(NSData *)d { 
    self = [self init]; 
    self.data = d; 
    return self; 
} 

@end 

---

@interface B : A 

@end 

---

#import "B.h" 

@implementation B 

- (id) init { 
    self = [super initWithData:nil]; 
    // some subclass specific init code here ... 
    return 
} 
@end 

---

使用B，

- (void) testInit{ 
    B * b = [[B alloc] init]; 
} 

Answer 1

你調用您的實現[self init]這是造成遞歸問題..

實現這種方式：

- (id) init { 
    self = [super init]; 
    //Basic empty init... 
    return self; 
} 

- (id) initWithData:(NSData *)d 
{ 
    self = [super init]; //<---- check this line. 

    if(self) 
    { 
     self.data = d; 
    } 
    return self; 
} 

//如果您正在尋找寫一些初始化代碼只有1次在以下能正常工作.....

-(void)oneTimeWrittenInitCode:(id)mySelf 
{ 
    //your init code which you wish to write one time goes here... 
}  

- (id) init { 
    self = [super init]; 
    if(self) 
    { 
     [self oneTimeWrittenInitCode:self]; 
    } 
    return self; 
} 

- (id) initWithData:(NSData *)d 
{ 
    self = [super init]; 

    if(self) 
    { 
     [self oneTimeWrittenInitCode:self]; 
     self.data = d; 
    } 
    return self; 
} 

Answer 2

它應該是：

- (instancetype) initWithData:(NSData *)d 
{ 
    if(self = [super init]) 
    { 
     _data = d; 
    } 
    return self; 
} 

Answer 3

查找「指定初始化程序」模式。它描述瞭如何在類層次結構中安排初始化方法和便利構造函數（又名工廠方法）。

Answer 4

下面是上述指定initilizer模式的一個例子，

#import 」Person.h」 

@implementation Person 
-(id) initWithAge:(int)theAge AndHeight:(int)theHeight AndName:(NSString *)theName { 
    if (self = [super init]){ 
    _age = theAge; 
    _height = thefleight; 
    _name = theName; 
    } 
    return self; 
} 

-(id) initwithAge:(int)theAge AndHeight:(int)theHeight { 
    return [self initWithAge:theAge AndHeight:theHeight AndName:nil]; 
} 

-(id) initwithAge:(int)theAge { 
    return [self initWithAge:theAge AndHeight:0]; 
} 

- (id)init { 
    return [self initwithAge:0]; 
} 
@end