iOS开发那些事儿（五）Objective-C浅拷贝与深拷贝

1. 
2. 浅拷贝：copy操作出来的对象指针直接指向模板的地址。即两个对象公用一块内存地址

    #import <Foundation/Foundation.h>
    int main(int argc, const char * argv[]) {
        @autoreleasepool {
            NSString * testStr          = @"connor";
            NSLog(@"testStr's Address   = %p",testStr);
   
            NSString * testStrCopy      = [testStr copy];
            NSLog(@"testStrCopy Address = %p",testStrCopy);
   
            NSArray * array             = @[@,@,@];
            NSLog(@"array Address       = %p",array);
   
            NSArray * copyArray         = [array copy];
            NSLog(@"copyArray Address   = %p",copyArray);
        }
        return ;
    }

   输出结果如下：

   DataStruct[11210:2189074] testStr's Address   　  = 0x100004280

   DataStruct[11210:2189074] testStrCopy Address　= 0x100004280

   DataStruct[11210:2189074] array Address            = 0x100300650

   DataStruct[11210:2189074] copyArray Address     = 0x100300650

3. 深拷贝：copy操作出来的对象指针直接指向新开辟的内存。即持有原对象的拷贝副本

    #import <Foundation/Foundation.h>
    #import "Father.h"
    int main(int argc, const char * argv[]) {
        @autoreleasepool {
            NSString * test     = @"a";
            NSLog(@"%p",test);
   
            NSString * testCopy = [test mutableCopy];
            NSLog(@"%p",testCopy);
        }
        return ;
    }

   输出结果如下：

   DataStruct[11355:2249168] 0x100004280

   DataStruct[11355:2249168] 0x100203cf0

4. Foundation总结大致如下：
   • 　　NS*类型的类调用Copy属于浅拷贝（例如NSString、NSArray等等）
   • 　　NS*类型的类调用MutableCopy属于深拷贝（例如NSString、NSArray等等）
   • 　　NSMutable*类型无论调用Copy或者MutableCopy都属于深拷贝
5. 拷贝构造：以上我们谈的都是Foundation中用到的深浅拷贝，如果我们自己定义了一个类。怎么去实现它的深浅拷贝呢？这里就要用到拷贝构造方法。iOS中默认NSObject是不遵循NSCopying（不变副本）、NSMutableCopying（可变副本）的，所以如果想一个对象可Copy，就必须实现其中两个协议并且重写copyWithZone、mutableCopyWithZone方法。
   • 　　下面我们定义一个Father类，来实现深拷贝：

      /** .h  */
      #import <Foundation/Foundation.h>
      @interface Father : NSObject<NSCopying>
      @property(nonatomic,copy)NSString * name;
      @end
     
      /** .m  */
      #import "Father.h"
     
      @implementation Father
      -(id)copyWithZone:(NSZone *)zone{
          Father * copyFather = [[self class]allocWithZone:zone];
          return copyFather;
      }
      @end

     写好了Father类我们在外界就可以利用copy的方法去copy出一个Father对象

      #import <Foundation/Foundation.h>
      #import "Father.h"
      int main(int argc, const char * argv[]) {
          @autoreleasepool {
              Father * fatherA = [[Father alloc]init];
              fatherA.name     = @"connor";
              NSLog(@"%p",fatherA);
     
              Father * fatherB = [fatherA copy];
              NSLog(@"%@",fatherB.name);
              NSLog(@"%p",fatherB);
          }
          return ;
      }

     输出结果：

     DataStruct[11383:2256524] 0x100206c80

     DataStruct[11383:2256524] (null)

     DataStruct[11383:2256524] 0x100300600

     从输出结果来看，两个Father实例的内存地址是不一样的我们实现了深拷贝。但是为什么第二个Father没有名字？在拷贝过程过虽然我是从你FatherA拷贝过来的，但是你并没有指定FatherA中的属性到底是什么方式拷贝过来。所以这里面如果想要实现名字也拷贝过来，需要我们自己去定义到底是深拷贝过来还是浅拷贝过来。这也符合苹果做事的风格嘛。

      #import "Father.h"
      //添加name的浅拷贝
      @implementation Father
      -(id)copyWithZone:(NSZone *)zone{
          Father * copyFather = [[self class]allocWithZone:zone];
          copyFather.name     = [self.name copy]; //如果想要深拷贝过来直接mutableCopy即可
          return copyFather;
      }
      @end

     结果输出两个name的内存地址：

     DataStruct[11409:2261412] 0x100004290

     DataStruct[11409:2261412] 0x100004290

   • 现在情况改变了，Father平时出门需要开车。Father需要持有Car类。那这个时候我们要如果复制这个爸爸！（因为复制出来的Father不能和之前那个Father开一辆车，所以我们应该用深拷贝。过程很简单直接贴代码了！）

      /** .h */
      #import <Foundation/Foundation.h>
     
      @interface Car : NSObject<NSCopying>
      @property(nonatomic,copy)NSString * brand;
      @end
     
      /** .m */
      @implementation Car
      -(id)copyWithZone:(NSZone *)zone{
          Car * copyCar = [[self class]allocWithZone:zone];
          copyCar.brand = [self.brand mutableCopy];
          return copyCar;
      }
      @end

     Car

     /** .h */
     #import <Foundation/Foundation.h>
     #import "Car.h"
     @interface Father : NSObject<NSCopying>
     @property(nonatomic,copy)NSString * name;
     @property(nonatomic,strong)Car    * car;
     @end
     
     /** .m */
     #import "Father.h"
     
     @implementation Father
     -(id)copyWithZone:(NSZone *)zone{
         Father * copyFather = [[self class]allocWithZone:zone];
         copyFather.name     = [self.name copy];
         copyFather.car      = [self.car copy];
         return copyFather;
     }
     @end

     Father

     #import <Foundation/Foundation.h>
     #import "Father.h"
     #import "Car.h"
     int main(int argc, const char * argv[]) {
         @autoreleasepool {
             Father * fatherA = [[Father alloc]init];
             fatherA.car      = [[Car alloc]init];
             NSLog(@"%p",fatherA.car);
     
             Father * fatherB = [fatherA copy];
             NSLog(@"%p",fatherB.car);
         }
         return ;
     }

     main

     输出结果：

     DataStruct[11441:2268004] 0x100111f60

     DataStruct[11441:2268004] 0x1001154a0

   • copy这种操作如果发生在继承关系之后就有什么样的效果？或者说1.父类实现了NSCopying，子类该如果实现NSCopying。2.父类没有实现NSCopying，子类如何实现NSCopying？要接一个问题我们先看下表象是什么，然后通过表象来分析问题并解决问题。接下来我们先试着用第一种情况来看看表象：Son继承于Father

      /** .h */
      #import "Father.h"
      @interface Son : Father
      @property(nonatomic,copy)NSString * toy;
      @end
     
      /** .m */
      #import "Son.h"
      @implementation Son
      @end

     Son

      #import <Foundation/Foundation.h>
      #import "Son.h"
      int main(int argc, const char * argv[]) {
          @autoreleasepool {
              Son * sonA = [[Son alloc]init];
              sonA.name  = @"connor";
              sonA.toy   = @"iPhone";
     
              Son * sonB = [sonA copy];
     
              NSLog(@"sonA's Address = %p",sonA);
              NSLog(@"sonB's Address = %p",sonB);
     
              NSLog(@"sonA's name Address = %p",sonA.name);
              NSLog(@"sonB's name Address = %p",sonB.name);
     
              NSLog(@"sonA's toy Address = %p",sonA.toy);
              NSLog(@"sonB's toy Address = %p",sonB.toy);
          }
          return ;
      }

     main

     输出结果：

     DataStruct[11563:2279201] sonA's Address 　　   = 0x100114bc0

     DataStruct[11563:2279201] sonB's Address          = 0x100111f70

     DataStruct[11563:2279201] sonA's name Address = 0x100004260

     DataStruct[11563:2279201] sonB's name Address = 0x726f6e6e6f6365

     DataStruct[11563:2279201] sonA's toy Address    = 0x100004280

     DataStruct[11563:2279201] sonB's toy Address = 0x0　　                                                                                这个结果也在我们意料之内的嘛，Son是继承与Father类的，Father实现了Copy协议，所以这个copy协议实现会继承到子类。我的理解其实：当Son调用Copy方法的时候就将消息转发给Son抽象类，发现Son中没有实现Copt则向Father发送消息SuperSendMsg就相当于事件响应链传递一样。一直向上传递直到能被处理。**这里需要注意一点Father中  Father * copyFather = [[self class]allocWithZone:zone];这里用的是self而不是Father因为Son会走到这里来，我们不能限制死到底是谁来调用***。接下来我们继续看为什么toy是个空置，这个原因和上面说的嵌套copy有点类似。因为Father不清楚你Son的属性到底是怎么copy过来的。那么怎么修改呢？我们只要在toy中稍作修改即可

      @implementation Son
      -(id)copyWithZone:(NSZone *)zone{
           //这句话保证父类的copy也被call到
          Son * son = [super copyWithZone:zone];
          son.toy   = [self.toy mutableCopy];
          return son;
      }
      @end

     Son

     输出结果：toy成功被深拷贝

     DataStruct[11606:2301994] sonA's toy Address = 0x100004288

     DataStruct[11606:2301994] sonB's toy Address = 0x656e6f68506965

   • 接下来我们看一下第二种情况，父类没有实现NSCopying，子类如何实现NSCopying。直接让子类去实现就好了呗。父类如果需要深拷贝的我延迟到子类去执行呗！(这里有个问题，我的Son没有继承NSCopying，但是重写CopyWithZone居然没有报错？？！！)

      #import "Son.h"
      @implementation Son
      -(id)copyWithZone:(NSZone *)zone{
      //    Son * son = [super copyWithZone:zone];
          Son * son = [[self class] allocWithZone:zone];
          son.name  = [self.name mutableCopy];
          son.toy   = [self.toy mutableCopy];
          return son;
      }
      @end

     Son

     输出结果：

     DataStruct[11660:2317623] sonA's Address          = 0x100206e00

     DataStruct[11660:2317623] sonB's Address          = 0x1002040e0

     DataStruct[11660:2317623] sonA's name Address = 0x100004260

     DataStruct[11660:2317623] sonB's name Address = 0x726f6e6e6f6365

     DataStruct[11660:2317623] sonA's toy Address    = 0x100004280

     DataStruct[11660:2317623] sonB's toy Address    = 0x656e6f68506965