IOS 面向接口编程 Objection基本原理

1、Objection 基本使用

例子：

1、Enginer

.h
@interface Enginer : NSObject
@end

.m
@implementation Enginer
objection_register(@"Enginer")
@end

2、Car

 .h
 @interface Car : NSObject
 @property(nonatomic, strong) Enginer *mEnginer;
 @end
.m
 @implementation Car
 objection_requires(@"mEnginer")
 @end

3、ViewController

.h
@property (nonatomic, strong) Car *mCar;
.m
- (void)viewDidLoad
{
   [super viewDidLoad];
   self.mCar = [[JSObjection createInjector]getObject:[Car class]];
}

在ViewController里面获取的Car 的实体，并且，Car里面的Enginer也会自动创建。

Objection原理解析

Objection 通过传入class，通过class name 字符串化后创建一个JSObjectionInjectorEntry,并且以class name为key 保存到字典中，在获取的时候获取这个injectorEntry，获取到class 后，创建对象。

注册： objection_register(@"类名")
声明需要注入的参数： objection_requires(@"对象名")
注入： [[JSObjection createInjector]getObject:[Car class]]

ojbection_register()

#definde objection_register(value)
+(void)initialize{
     if(self == [value class]){
        [[JSObjection registerClass:[value class] scope: JSObjectionScopeNormal];
  }    
}

这个是到底做了什么呢？

static NSMutableDictionary *gObjectionContext

+（void）registerClass:(Class)theClass scope:(JSObjectionScope)scope

//核心代码
[gObjectionContext 
 setObject:[JSObjectionInjectorEntry entryWithClass: theClass scope:scope] 
 forKey: NSStringFromClass(theClass) ];

---

从上面可以看出来，实际上就是将一个JSObjectionInjectorEntry ，保存到一个以类名对应的一个字典里面。

那这个JSObjectionInjectorEntry 是什么东西呢？

typedef enum{
  JSObjectionScopeNone = -1,
  JSObjectionScopeNormal ,
 JSObjecitonScopeSingleton
}

@interface JSObjectionInjectorEntry : JSObjectionEntry
  @property (nonatomic, readonly) Class classEntry;
@end

@interface JSObjectionInjectorEntry ()
      JSObjectionScope _lifeCycle;
      id _storageCache;
@end

@implement
   + (id)entryWithClass: (Class) theClass scope:(JSObjectionScope)theLifeCycle{
return [[JSObjectionInjectorEntry alloc]initWithClass:theClass lifeCycle:thelifeCycle];
}

- (instancetype)initWithClass:(Class)theClass lifeCycle:(JSObjectionScope)theLifeCycle{
   _lifeCycle = thelifeCycle;
   _classEntry = theClass;
  _storageCache = nil;
}
@end

从上面的代码可以看出来，JSObjectionInjectorEntry 保存了
1、class _ckassEntry
2、JSObjectionScope lifeCycle

从上面可以看出来，注册就是把class name 和 JSObjectionInjectiorEnry用字典保存到gObjectionContext ，Entry保存的了Class 和 lifeCycle.

2、 objection_requires()获取参数

这里就一个方法，会返回一个需要注入的参数列表

#define objection_requires(args...)
     +(NSSet *)objectionRequires{
       NSSet *requirements = [NSSet setWithObjects： args, nil];
       return JSObjectionUtils.buildDependenciesForClass(self, requirements);
  }

static NSSet *BuildDependenciesForClass(Class klass, NSSet*requirements){
   Class superClass = class_getSuperclass([klass class]);
    .....
retrunn requirements;
}

3、注入

通过class获取到注入器, 通过注入器获取到实例

JSObjectionInjector

-(id)getObjectWithArgs:(id)classOrProtocol,...{
     va_list va_arguments;
     va_start(va_arguments, classOrProtocol);
     id object = [self getObject:classOrProtocol arguments:va_arguments];
     va_end(va_arguments);
return object;
}

- (id)getObject:(id)classOrProtocol name:(NSString *)name initializer:(SEL)selector arguments:(NSArray *)argumentList {
       1、通过classOrProtocol 获取key,及class name str
       2、获取injectorEntry
             injectorEntry = [JSObjectionInjectorEntry entryWithClass scope:JSObjectionScopeNormal];
            injectorEntry.injector = self;
            _context setObject:injectorEntry forKey：key

      3、通过injectorEntry 获取实例对象
          [injectorEntry extractObject：argumentList  initializer:selector];
         -(id)buidlObject:(NSArray *)arguments  initializer:(SEL) initializer;
}