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，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 @encodetype 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.