[IOS 开发] iOS中的RunTime机制

一、首先我们要先知道object-c是一门编译型、动态语言（这里强调下oc是静态类型语言），这在开发语言中是并多见的，一般的动态语言多为解释性语言。oc之所以能够做到即使编译型语言，又是动态语言。就是得益于RunTime机制。

由于本文主要讲解的是RunTime机制，所以语言类型不做过多描述，之后可以另写一篇语言类型的介绍。

二、这里主要讲解RunTime如何使用，其中主要的知识点如下：

1、class_copyPropertyList  获取一份拷贝的成员列表数组

2、property_getName获取成员名称

3、class_getInstanceVariable  获取成员对象的Ivar

4、object_getIvar从Ivar对象中取值

5、object_setIvar赋值函数

下面我们来看一下代码实现：

1、创建一个类

CustomClass.h

#import <Foundation/Foundation.h>

@interface CustomClass : NSObject

@property (nonatomic , strong) NSString *age;

- (void)test;

@end

CustomClass.m
#import "CustomClass.h"

@implementation CustomClass

- (void)test
{
NSLog(@"这里是CustomClass");

}

@end
接下来创建一个类别来实现RunTime机制

NSObject+RunTimeTest.h
#import <Foundation/Foundation.h>

@interface NSObject (RunTimeTest)

//动态创建一个类，之后为这个类的age属性赋值。
- (id) testRunTime:(NSString *)classname age:(NSString *)age;

@end

NSObject+RunTimeTest.m
#import "NSObject+RunTimeTest.h"
#import <objc/runtime.h>
#import "CustomClass.h"

@implementation NSObject (RunTimeTest)

- (CustomClass *)testRunTime:(NSString *)classname age:(NSString *)age
{
// propertyCount 成员属性的数量
unsigned int propertyCount = 0;
/* objc_property_t 根据苹果文档的解释：An opaque type that represents an Objective-C declared property.
个人理解：一个任意类型的对象代表一个oc声明的属性成员 （本人英语水平实在有限）*/
/* class_copyPropertyList
文档：Return Value
An array of pointers of type objc_property_t describing the properties declared by the class. Any properties declared by superclasses are not included. The array contains *outCount pointers followed by a NULL terminator. You must free the array with free().
个人理解：主要2个意思：返回一个数组指针，类型为objc_property_t，用完要记得free，释放掉。
*/
objc_property_t *properties = class_copyPropertyList([self class], &propertyCount);
for (unsigned int i = 0; i < propertyCount; i++) {
objc_property_t property = properties[i];
//获取成员的名称
NSString *propertyName = [[NSString alloc] initWithCString:property_getName(property) encoding:NSUTF8StringEncoding];
NSLog(@"propertyName = %@ -- 成员名称",propertyName);

//获取成员内容的Ivar
Ivar iVar = class_getInstanceVariable([self class], [propertyName UTF8String]);
//其实上面那行获取代码是为了保险起见，基本是获取不到内容的。因为成员的名称默认会在前面加"_" ，
if (iVar == nil) {
iVar = class_getInstanceVariable([self class], [[NSString stringWithFormat:@"_%@",propertyName] UTF8String]);
}

// 取值
id propertyVal = object_getIvar(self, iVar);
NSLog(@"propertyVal = %@ --值",propertyVal);

// 动态创建类
Class varClass = NSClassFromString(classname);
id varObj = [[varClass alloc] init];
//调用新创建类的方法，这里要主要一定引入对应得头文件，不然调用方法会不错。
[varObj test];

Ivar iVarObj = class_getInstanceVariable(varClass, [@"_age" UTF8String]);

object_setIvar(varObj, iVarObj, age);

return varObj;
}
return nil;

}

@end
测试：

ViewController.m
#import "NSObject+RunTimeTest.h"
#import "CustomClass.h"

@interface ViewController ()

@property (nonatomic , strong) NSString *name;

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.

_name = @"xiaonan";
CustomClass *tmp = [self testRunTime:@"CustomClass" age:@"098"];
NSLog(@"tmp.age = %@",tmp.age);

}

结果输出：
2014-11-29 17:16:55.483 TestRunTime2[21001:176367] propertyName = name -- 成员名称
2014-11-29 17:16:55.483 TestRunTime2[21001:176367] propertyVal = xiaonan --值
2014-11-29 17:16:55.484 TestRunTime2[21001:176367] 这里是CustomClass
2014-11-29 17:16:55.484 TestRunTime2[21001:176367] tmp.age = 098