iOS底层学习-day-16

前言-OC-runtime篇

我是一名iOS开发者， iOS底层 菜鸟的进阶之路30天。

问题

什么是Runtime？平时项目中有用过么？

• OC是一门动态性比较强的编程语言，允许很多操作推迟到程序运行时再进行
• OC的动态性就是由Runtime来支撑和实现的，Runtime是一套C语言的API，封装了很多动态性相关的函数
• 平时编写的OC代码，底层都是转换成了Runtime API进行调用

Runtime 具体应用

• 利用关联对象（AssociatedObject）给分类添加属性
• 遍历类的所有成员变量（修改textfield的占位文字颜色、字典转模型、自动归档解档）
• 交换方法实现（交换系统的方法）
• 利用消息转发机制解决方法找不到的异常问题

runtime API-01 类

• 获取isa指向的Class

Class object_getClass(id obj)

• 设置isa指向的Class

Class object_setClass(id obj, Class cls)
object_setClass(person,@selector(run));

• 判断一个OC对象是否为Class

BOOL object_isClass(id obj)
NSLog(@"%d %d %d",
          object_isClass(person),//object_isClass查看是不是类对象
          object_isClass([MJPerson class]),
          object_isClass(object_getClass([MJPerson class]))
          );

• 动态创建一个类（参数：父类，类名，额外的内存空间）// 成员变量是不能动态添加的，因为他是只读的class_ro_t

Class objc_allocateClassPair(Class superclass, const char *name, size_t extraBytes)

• 动态添加成员变量（已经注册的类是不能动态添加成员变量的）

BOOL class_addIvar(Class cls, const char * name, size_t size, uint8_t alignment, const char * types)

• 例子1

	void run(id self, SEL _cmd) {
    	NSLog(@"_____ %@ - %@", self, NSStringFromSelector(_cmd));
	}
	// 创建类
    Class newClass = objc_allocateClassPair([NSObject class], "MJDog", 0);
    class_addIvar(newClass, "_age", 4, 1, @encode(int));
    class_addIvar(newClass, "_weight", 4, 1, @encode(int));
    class_addMethod(newClass, @selector(run), (IMP)run, "v@:");
    // 注册类
    objc_registerClassPair(newClass);

//    MJPerson *person = [[MJPerson alloc] init];
//    object_setClass(person, newClass);
//    [person run];//这时候就跑到了newClass来了
    
    id dog = [[newClass alloc] init];
    [dog setValue:@10 forKey:@"_age"];
    [dog setValue:@20 forKey:@"_weight"];
    [dog run];
    
    NSLog(@"%@ %@", [dog valueForKey:@"_age"], [dog valueForKey:@"_weight"]);
    
    // 在不需要这个类时释放
    objc_disposeClassPair(newClass); //释放类

• 设置和获取成员变量的值

void object_setIvar(id obj, Ivar ivar, id value)
id object_getIvar(id obj, Ivar ivar)

• 获取一个实例变量信息

Ivar class_getInstanceVariable(Class cls, const char *name)

• 拷贝实例变量列表（最后需要调用free释放）

Ivar *class_copyIvarList(Class cls, unsigned int *outCount)

• 获取成员变量的相关信息

const char *ivar_getName(Ivar v)
const char *ivar_getTypeEncoding(Ivar v)

• 例子2

 	// 获取成员变量信息
    Ivar ageIvar = class_getInstanceVariable([MJPerson class], "_age");
    NSLog(@"%s %s", ivar_getName(ageIvar), ivar_getTypeEncoding(ageIvar));

    // 设置和获取成员变量的值
    Ivar nameIvar = class_getInstanceVariable([MJPerson class], "_name");
    
    MJPerson *person = [[MJPerson alloc] init];
    object_setIvar(person, nameIvar, @"123");
    object_setIvar(person, ageIvar, (__bridge id)(void *)10);
    NSLog(@"%@ %d", person.name, person.age);

    // 成员变量的数量
    unsigned int count;
    Ivar *ivars = class_copyIvarList([MJPerson class], &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[I];//*[ivars + i]
        NSLog(@"%s %s", ivar_getName(ivar), ivar_getTypeEncoding(ivar));
    }
    free(ivars);

字典转模型例子

• NSObject+Json.h

#import <Foundation/Foundation.h>

@interface NSObject (Json)

+ (instancetype)mj_objectWithJson:(NSDictionary *)json;

@end

• NSObject+Json.m

#import "NSObject+Json.h"
#import <objc/runtime.h>

@implementation NSObject (Json)

+ (instancetype)mj_objectWithJson:(NSDictionary *)json {
    id obj = [[self alloc] init];
    
    unsigned int count;
    Ivar *ivars = class_copyIvarList(self, &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[i];
        NSMutableString *name = [NSMutableString stringWithUTF8String:ivar_getName(ivar)];
        [name deleteCharactersInRange:NSMakeRange(0, 1)];
        
        // 设值
        id value = json[name];
        if ([name isEqualToString:@"ID"]) {
            value = json[@"id"];
        }
        [obj setValue:value forKey:name];
    }
    free(ivars);
    
    return obj;
}

@end

runtime API-04 方法替换

• 拷贝方法列表（最后需要调用free释放）

Method *class_copyMethodList(Class cls, unsigned int *outCount)

• 动态添加方法

BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types)

• 获取方法的相关信息（带有copy的需要调用free去释放）

SEL method_getName(Method m)
IMP method_getImplementation(Method m)
const char *method_getTypeEncoding(Method m)
unsigned int method_getNumberOfArguments(Method m)
char *method_copyReturnType(Method m)
char *method_copyArgumentType(Method m, unsigned int index)

• 获得一个实例方法、类方法

Method class_getInstanceMethod(Class cls, SEL name)
Method class_getClassMethod(Class cls, SEL name)

• 方法实现相关操作重要

IMP class_getMethodImplementation(Class cls, SEL name) 

IMP method_setImplementation(Method m, IMP imp)

void method_exchangeImplementations(Method m1, Method m2) 

• method_exchangeImplementations

MJPerson *person = [[MJPerson alloc] init];
        
Method runMethod = class_getInstanceMethod([MJPerson class], @selector(run));
Method testMethod = class_getInstanceMethod([MJPerson class], @selector(test));
method_exchangeImplementations(runMethod, testMethod);

[person run];//就变成test

• 动态替换方法重要

IMP class_replaceMethod(Class cls, SEL name, IMP imp, const char *types)

• class_replaceMethod

MJPerson *person = [[MJPerson alloc] init];
//class_replaceMethod([MJPerson class], @selector(run), (IMP)myrun, "v");
    
class_replaceMethod([MJPerson class], @selector(run), imp_implementationWithBlock(^{
     NSLog(@"123123");
}), "v");
    
[person run];