我理解的iOS中的RunTime机制（1）

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

原文地址：http://blog.csdn.net/qqmcy/article/details/41596725