OC基础-内存管理（二）MyArray解释addObject原理
一、看MutableArray中的addObject之后的retainCount
Dog.h
#import <Foundation/Foundation.h>
@interface Dog : NSObject
{
int _ID;
}
@property (assign) int ID;
@endDog.m
#import "Dog.h"
@implementation Dog
@synthesize ID = _ID;
//重写该方法，该方法自动会调用
-(void)dealloc{
NSLog(@"dog id %d is dealloc", _ID);
[super dealloc];
}
@end
main.m
#import <Foundation/Foundation.h>
#import "Dog.h"
int main(int argc, const char * argv[]) {
@autoreleasepool {
NSMutableArray * array = [[NSMutableArray alloc] init];
for(int x = 0; x <5; x++){
Dog * d = [[Dog alloc] init];
[d setID: x];
NSLog(@"dog retainCount is %ld", [d retainCount]);
[array addObject:d];
NSLog(@"dog retainCount2 is %ld", [d retainCount]);
[d release];
}
[array release];
}
return 0;
}输出结果：
2015-10-02 19:11:18.605 内存管理-MyArray[1770:59076] dog retainCount is 1 2015-10-02 19:11:18.606 内存管理-MyArray[1770:59076] dog retainCount2 is 2 2015-10-02 19:11:18.606 内存管理-MyArray[1770:59076] dog retainCount is 1 2015-10-02 19:11:18.606 内存管理-MyArray[1770:59076] dog retainCount2 is 2 2015-10-02 19:11:18.607 内存管理-MyArray[1770:59076] dog retainCount is 1 2015-10-02 19:11:18.607 内存管理-MyArray[1770:59076] dog retainCount2 is 2 2015-10-02 19:11:18.607 内存管理-MyArray[1770:59076] dog retainCount is 1 2015-10-02 19:11:18.607 内存管理-MyArray[1770:59076] dog retainCount2 is 2 2015-10-02 19:11:18.608 内存管理-MyArray[1770:59076] dog retainCount is 1 2015-10-02 19:11:18.608 内存管理-MyArray[1770:59076] dog retainCount2 is 2 2015-10-02 19:11:18.608 内存管理-MyArray[1770:59076] dog id 0 is dealloc 2015-10-02 19:11:18.608 内存管理-MyArray[1770:59076] dog id 1 is dealloc 2015-10-02 19:11:18.608 内存管理-MyArray[1770:59076] dog id 2 is dealloc 2015-10-02 19:11:18.608 内存管理-MyArray[1770:59076] dog id 3 is dealloc 2015-10-02 19:11:18.609 内存管理-MyArray[1770:59076] dog id 4 is dealloc Program ended with exit code: 0分析：
for循环四次，每次都进行相同的操作，目的是在数组中添加一个dog对象。
每次创建一个dog对象，retainCount=1，对象被引用次数为1，也就是自身保留，不被释放；
然后使用addObject方法，将对象添加到数组中，该对象的引用次数为2，除了自身之外，还被数组保留；
然后[d release]，使得retainCount=1, 自身保留引用被删除，该对象只被数组拥有。
[array release]，先释放数组中的dog对象，数组然后才被释放。
二、使用自定义数组分析addObject函数到底进行了操作
在上面的例子中，调用addObject方法后，retainCount就会+1，那其中到底进行了什么操作呢?
下面自己创建一个简单的数组类，来模拟其中的操作
MyArray.h
#import <Foundation/Foundation.h>
//创建一个简易版的数组来分析addObject内部的操作。
@interface MyArray : NSObject
{
NSUInteger _count; //数组元素个数
id _objs[512]; //创建一个512个元素的数组，大小4x512字节
}
@property (assign, readonly)NSUInteger count;
-(void)addObject: (id)object;
-(id)objectAtIndex: (NSUInteger)index;
-(void)removeObjectAtIndex: (NSUInteger)index;
-(void)removeAll;
@endMyArray.m
#import "MyArray.h"
@implementation MyArray
@synthesize count = _count;
-(id) init{
self = [super init];
if(self){
_count = 0;
}
return self;
}
-(void)addObject:(id)object{
if(_count > 512){
return;
}
_objs[_count] = [object retain];
_count++;
//这里必须retain一次。因为如果外部调用了该方法，然后又调用了release，那么这里存的就是一个野指针。
}
-(id)objectAtIndex:(NSUInteger)index{
return _objs[index];
}
-(void)removeObjectAtIndex:(NSUInteger)index{
id obj = _objs[index];
[obj release];
//因为添加元素的时候有retain一次，这里必须release
_objs[index] = nil;
}
-(void)removeAll{
for(int i = 0; i<_count; i++){
[self removeObjectAtIndex: i];
}
}
-(void)dealloc{
NSLog(@"before remove all");
[self removeAll];
NSLog(@"after remove all");
[super dealloc];
}
@end
main.m
#import <Foundation/Foundation.h>
#import "Dog.h"
#import "MyArray.h"
int main(int argc, const char * argv[]) {
@autoreleasepool {
#if 0
NSMutableArray * array = [[NSMutableArray alloc] init];
for(int x = 0; x <5; x++){
Dog * d = [[Dog alloc] init];
[d setID: x];
NSLog(@"dog retainCount is %ld", [d retainCount]);
[array addObject:d];
NSLog(@"dog retainCount2 is %ld", [d retainCount]);
[d release];
}
[array release];
#endif
MyArray * array = [[MyArray alloc] init];
for(int x = 0 ; x< 5; x++){
Dog * d = [[Dog alloc] init];
[d setID:x];
NSLog(@"dog retainCount is %ld", [d retainCount]);
[array addObject:d];
NSLog(@"dog retainCount2 is %ld", [d retainCount]);
[d release];
}
[array release];
}
return 0;
}
对比自定义数组的代码和OC提供的数组代码，操作很相似。
查看输出结果：
2015-10-02 19:43:03.291 内存管理-MyArray[2297:69892] dog retainCount is 1 2015-10-02 19:43:03.293 内存管理-MyArray[2297:69892] dog retainCount2 is 2 2015-10-02 19:43:03.293 内存管理-MyArray[2297:69892] dog retainCount is 1 2015-10-02 19:43:03.293 内存管理-MyArray[2297:69892] dog retainCount2 is 2 2015-10-02 19:43:03.293 内存管理-MyArray[2297:69892] dog retainCount is 1 2015-10-02 19:43:03.293 内存管理-MyArray[2297:69892] dog retainCount2 is 2 2015-10-02 19:43:03.294 内存管理-MyArray[2297:69892] dog retainCount is 1 2015-10-02 19:43:03.294 内存管理-MyArray[2297:69892] dog retainCount2 is 2 2015-10-02 19:43:03.294 内存管理-MyArray[2297:69892] dog retainCount is 1 2015-10-02 19:43:03.294 内存管理-MyArray[2297:69892] dog retainCount2 is 2 2015-10-02 19:43:03.295 内存管理-MyArray[2297:69892] before remove all 2015-10-02 19:43:03.295 内存管理-MyArray[2297:69892] dog id 0 is dealloc 2015-10-02 19:43:03.295 内存管理-MyArray[2297:69892] dog id 1 is dealloc 2015-10-02 19:43:03.295 内存管理-MyArray[2297:69892] dog id 2 is dealloc 2015-10-02 19:43:03.295 内存管理-MyArray[2297:69892] dog id 3 is dealloc 2015-10-02 19:43:03.296 内存管理-MyArray[2297:69892] dog id 4 is dealloc 2015-10-02 19:43:03.296 内存管理-MyArray[2297:69892] after remove all Program ended with exit code: 0
从上面可以看出输出结果和之前的是一样的，也就是说在addObject函数内部实际上是进行了retain操作，而在removeObject函数中相应的进行了release操作，每一个release对应一个retain，严格遵守黄金法则。
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