object c++怎么实现反射机制

2012-07-26

object c++如何实现反射机制object c++如何实现反射机制?开发语言的反射机制为我们提供了发挥想象力的基础

object c++如何实现反射机制

开发语言的反射机制为我们提供了发挥想象力的基础，通过反射可以设计出各种5花8门的架构来。

参考网上各种资料，Object c++的反射主要依靠下面的2个函数。

NSClassFromString

NSSelectorFromString

下面直接摆上例子，一目了然。

（一）通过一个字符串来创建对象并调用对象中的方法。

文件:Member.h

//  Member.h#import <Foundation/Foundation.h>@interface Member : NSObject {NSString *name;int age;}@property (nonatomic,copy) NSString *name;@property int age;@end

文件Member.m

//  Member.m#import "Member.h"@implementation Member@synthesize name,age;@end

测试代码文件Sample01.m:

#import <Foundation/Foundation.h>int main (int argc, const char * argv[]) {    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];//定义类名NSString *className=@"Member";//定义方法名//注意：方法名后面要根据参数来设置，这里的setName:，表示setName//     方法后面有1个参数NSString *methodName=@"setName:";//取得类并分配内存和初始化id obj=[[NSClassFromString(className) alloc] init];//调用类方法[obj performSelector: NSSelectorFromString(methodName) withObject:@"Tom and Jerry."];//显示NSLog(@"%@",[obj name]);[pool drain];    return 0;}

代码执行后，显示如下：

2012-03-16 17:41:31.962 Sample01[39762:1307] Tom and Jerry.

由上面例子发现：

（1）在反射时，不需要使用import引入要反射的类；

（2）在定义反射类方法名时要注意后面的冒号，必须根据参数数量和原类方法名设置。

（二）通过字符串获取类的全部属性。

对上面的例子进行调整，如下面代码：（注意：在头部要引入头文件 objc/runtime.h）

#import <Foundation/Foundation.h>#import <objc/runtime.h>int main (int argc, const char * argv[]) {    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];//定义类名NSString *className=@"Member";//定义方法名//注意：方法名后面要根据参数来设置，这里的setName:，表示setName//     方法后面有1个参数NSString *methodName=@"setName:";//取得类并分配内存和初始化id obj=[[NSClassFromString(className) alloc] init];//调用类方法[obj performSelector: NSSelectorFromString(methodName) withObject:@"Tom and Jerry."];//显示NSLog(@"%@",[obj name]);//定义类属性的数量unsigned propertyCount;//获取对象的全部属性并循环显示属性名称和属性特性参数objc_property_t *properties = class_copyPropertyList([obj class],&propertyCount);for(int i=0;i<propertyCount;i++){objc_property_t prop=properties[i];NSLog(@"property:%s",property_getName(prop));NSLog(@"property_getAttributes:%s",property_getAttributes(prop));}[pool drain];    return 0;}

代码执行后，显示结果如下：

2012-03-19 16:40:04.345 Sample01[41713:1307] Tom and Jerry.

2012-03-19 16:40:04.350 Sample01[41713:1307] property:age

2012-03-19 16:40:04.352 Sample01[41713:1307] property_getAttributes:Ti,Vage

2012-03-19 16:40:04.354 Sample01[41713:1307] property:name

2012-03-19 16:40:04.355 Sample01[41713:1307] property_getAttributes:T@"NSString",C,N,Vname

关于属性的特性参数可以参考官方文档说明：

Property Type String
You can use the?`property_getAttributes`?function to discover the name, the?`@encode`type string of a property, and other attributes of the property.
The string starts with a?`T`?followed by the?`@encode`?type and a comma, and finishes with a?`V`?followed by the name of the backing instance variable. Between these, the attributes are specified by the following descriptors, separated by commas:
Table 7-1??Declared property type encodings
Code
Meaning
`R`
The property is read-only (`readonly`).
`C`
The property is a copy of the value last assigned (`copy`).
`&`
The property is a reference to the value last assigned (`retain`).
`N`
The property is non-atomic (`nonatomic`).
`G<name>`
The property defines a custom getter selector name. The name follows the?`G`?(for example,?`GcustomGetter,`).
`S<name>`
The property defines a custom setter selector name. The name follows the?`S`?(for example,?`ScustomSetter:,`).
`D`
The property is dynamic (`@dynamic`).
`W`
The property is a weak reference (`__weak`).
`P`
The property is eligible for garbage collection.
`t<encoding>`
Specifies the type using old-style encoding.

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