Object-c 内存一些事-优快云博客

本文探讨了Objective-C中不同对象释放方式的影响，通过实例对比了使用self.xxx=nil与[xxx release]的区别，揭示了[super dealloc]调用时机的重要性。

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 1 @interface ClassC : NSObject {
 2 @private
 3     
 4 }
 5 @end
 6 
 7 @implementation ClassC
 8 
 9 -(void) dealloc
10 {
11     [super dealloc];
12      
13 }
14 @end
15 
16 @interface ClassB : NSObject {
17 @private
18     ClassC * class_c;
19 }
20 
21 @property(nonatomic, retain) ClassC * classc;
22 @end
23 
24 @implementation ClassB
25 
26 @synthesize classc = class_c;
27 -(id) init
28 {
29     if (self = [super init]) {
30         class_c = [[ClassC alloc] init];
31     }
32     
33     return self;
34 }
35 
36 -(void) dealloc
37 {
38     [super dealloc];
39     self.classc = Nil;
40 //    [class_c release];
41 }
42 @end

调用如下：

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    
    ClassB * b = [[ClassB alloc] init];
    [b release];
   [pool release];
}

根据调试的结果，在ClassB的dealloc中使用:self.classc = Nil;也可以执行到ClassC的dealloc方法, 说明使用self.classc = Nil & self.classc = nil & [class_c release]的效果都是一样的。

如果在ClassB的init方法不去初始化 class_c 执行[class_c release] 也不会出错，因为ios中向一个空的对象发送消息是没有问题的。

在ClaasB中

-(void) dealloc
{
    [super dealloc];
//    self.classc = nil;
    [class_c release];
//    class_c = nil;
    
    [class_c release];
    class_c = nil;

}

也不会有问题。

但是，在ClassB中如下就出问题了

@interface ClassB : NSObject {
@private
    ClassC * class_c;
    ClassC * class_c1;
    ClassC * class_c2;
}

@property(nonatomic, retain) ClassC * classc;
@property(nonatomic, retain) ClassC * classc1;
@property(nonatomic, retain) ClassC * classc2;

-(void) test;
@end

@implementation ClassB

@synthesize classc = class_c;
@synthesize classc1 = class_c1;
@synthesize classc2 = class_c2;
-(id) init
{
    if (self = [super init]) {
        class_c = [[ClassC alloc] init];
        class_c1 = [[ClassC alloc] init];
        class_c2 = [[ClassC alloc] init];
    }
    
    return self;
}

-(void) test
{
    self.classc = self.classc1;
    self.classc1 = self.classc2;
    self.classc2 = nil;
    
    
}
-(void) dealloc
{
    [super dealloc];
    self.classc = Nil;   // = nil 也是一样的
    self.classc1 = Nil;
    self.classc2 = Nil;
//    [class_c release];
//    class_c = nil;
//    
//    [class_c1 release];
//    class_c1 = nil;
//    
//    [class_c2 release];
//    class_c2 = nil;
    

}
@end

这样在[b release];的时候就报了 EXC_BAD_ACCESS错误，好换种写法：

-(void) dealloc
{
    [super dealloc];
//    self.classc = nil;
//    self.classc1 = nil;
//    self.classc2 = nil;
    [class_c release];
    class_c = nil;
    
    [class_c1 release];
    class_c1 = nil;
    
    [class_c2 release];
    class_c2 = nil;
    

}

这次就正确了，没有任何错误，得到结论1：在释放对象的时候，使用 [xxx release]; 尽量不要使用self.xxxx = nil这种方式。

此时多调用几次

    [b test];
    [b test];
    [b test];
    [b test];

也没有错误，再试下不初始化三个class_c 也是没有问题的。

但是：我们之前也有得到一个结论：说明使用self.classc = Nil & self.classc = nil & [class_c release]的效果都是一样的。

那这两个结论不是矛盾的么？其中的原因到底是为什么？我接着做了如下尝试：

@interface ClassB : NSObject {
@private
    ClassC * class_c;
    ClassC * class_c1;
    ClassC * class_c2;
}

@property(nonatomic, retain) ClassC * classc;
@property(nonatomic, retain) ClassC * classc1;
@property(nonatomic, retain) ClassC * classc2;

-(void) test;
@end

@implementation ClassB

@synthesize classc = class_c;
@synthesize classc1 = class_c1;
@synthesize classc2 = class_c2;
-(id) init
{
    if (self = [super init]) {
        class_c = [[ClassC alloc] init];
        class_c1 = [[ClassC alloc] init];
        class_c2 = [[ClassC alloc] init];
    }
    
    return self;
}

-(void) test
{
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    self.classc = self.classc1;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    self.classc1 = self.classc2;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    
    self.classc2 = nil;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
}

-(void) dealloc
{
    [super dealloc];  
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    self.classc = nil;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    self.classc1 = nil;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);    
    self.classc2 = nil;
    
    
//    [class_c release];
//    class_c = nil;
//    
//    [class_c1 release];
//    class_c1 = nil;
//    
//    [class_c2 release];
//    class_c2 = nil;
    

}

这样结果也是一样的，很崩溃，在ClassB的dealloc方法里面，没关系再试试，我重新尝试了一下

-(void) dealloc
{
     
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    self.classc = nil;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);
    self.classc1 = nil;
    
    NSLog(@"class_c is :%d", class_c.retainCount);
    NSLog(@"class_c1 is :%d", class_c1.retainCount);
    NSLog(@"class_c2 is :%d", class_c2.retainCount);    
    self.classc2 = nil;
    [super dealloc];  
}

这时候竟然神一样的没有问题了，不同的地方就是[ super dealloc ] 这句，放到后面就正确了，再做如下两个实验：

-(void) dealloc
{

    [class_c release];
    class_c = nil;
    
    [class_c1 release];
    class_c1 = nil;
    
    [class_c2 release];
    class_c2 = nil;
    [super dealloc];  

}

-(void) dealloc
{
    
    [super dealloc];  
    
    [class_c release];
    class_c = nil;
    
    [class_c1 release];
    class_c1 = nil;
    
    [class_c2 release];
    class_c2 = nil;
    

}

这两种都是可以正确执行的，没有问题，那么问题的核心就在 [super delloc] 到底对 sekf.xxxx = nil 有什么影响？

转载于:https://www.cnblogs.com/GnagWang/archive/2011/11/14/2248134.html