前言

上篇主要講Runtime的一些術語描述和定義去枷，Runtime的主要應用是用于消息的傳遞，今天會結合一些實戰(zhàn)例子來講下OC的消息傳遞機制。

普通消息傳遞

在OC里删顶，對象調用方法叫作發(fā)送消息疗隶，對象調用方法在Runtime里被轉化為objc_msgSend函數(shù)來實現(xiàn)

[receiver oneMethod];
//transfer to ：
objc_msgSend(receiver, @selector(oneMethod));

Runtime會根據(jù)類型自動轉換為下列某個函數(shù)：

objc_msgSend：普通的消息都會通過該函數(shù)發(fā)送；
objc_msgSend_stret：消息中有數(shù)據(jù)結構作為返回值（不是簡單值）時翼闹，通過此函數(shù)發(fā)送和接收返回值斑鼻；
objc_msgSendSuper：和objc_msgSend類似，這里把消息發(fā)送給父類的實例猎荠；
objc_msgSendSuper_stret：和objc_msgSend_stret類似坚弱，這里把消息發(fā)送給父類的實例并接收返回值；

objc_msgSend的調用過程

1. 先檢查這個selector是否存在关摇，不存在則忽略荒叶；
2. 接著檢查selector的target是否為nil，向nil對象發(fā)送任何消息都會被忽略掉输虱；
3. 前面兩步?jīng)]問題些楣，則先在isa指針指向的class的cache里面找有沒有方法調用記錄，如果有宪睹，則運行對應的函數(shù)愁茁，如果沒有則在class的methodLists查找方法，沒有則通過super_class指針找到父類的類對象結構體亭病，然后從methodLists查找方法鹅很，如果仍找不到，則繼續(xù)通過
super_class向上一級父類結構體中查找罪帖，直到根類（NSObject）促煮；
4. 如果還是找不到，則進入消息動態(tài)解析整袁；

消息動態(tài)解析

動態(tài)解析流程圖：

objective-runtime-6.png

具體解析：
1. 通過resolveInstanceMethod菠齿，該方法決定是否動態(tài)添加方法。如果返回YES坐昙，則通過class_addMethod動態(tài)添加方法绳匀，消息得到處理，結束民珍；如果返回NO襟士，則進入下一步；
2. 這一步會步入forwardingTargetForSelector方法嚷量，用于指定備選對象響應這個selector，不能指定為self逆趣，如果放回某個對象則會調用對象的方法蝶溶，結束。如果放回nil，則進入第三步抖所；
3. 這一步梨州，我們通過methodSignatureForSelector進行方法簽名，如果返回nil田轧，則消息無法處理暴匠。如果返回methodSignature則進入下一步；
4. 這步調用forwardInvocation方法傻粘，我們通過anInvocation對象做很多處理每窖，比如修改實現(xiàn)方法，修改響應對象弦悉，如果方法方法調用成功窒典，則結束。如果失敗稽莉，則進入doesNotRecognizeSelector瀑志，如果沒有實現(xiàn)這個方法會crash

實戰(zhàn)

通過runtime動態(tài)創(chuàng)建類和對象

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/message.h>
void sayFunction(id self, SEL _cmd, id some){
    
    NSLog(@"%@歲的%@說：%@",object_getIvar(self, class_getInstanceVariable([self class], "_age")),object_getIvar(self, class_getInstanceVariable([self class], "_name")),some);
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        //動態(tài)創(chuàng)建類
        Class MyPeople = objc_allocateClassPair([NSObject class], "Person", 0);
        
        //為類添加成員變量
        class_addIvar(MyPeople, "_name", sizeof(NSString*), log2(sizeof(NSString*)), @encode(NSString*));
        class_addIvar(MyPeople, "_age", sizeof(int),sizeof(int),@encode(int));
        
        //注冊方法（"v@:@"代表返回值+參數(shù)列表）
        SEL say = sel_registerName("say:");
        class_addMethod(MyPeople, say, (IMP)sayFunction, "v@:@");
        
        //注冊類
        objc_registerClassPair(MyPeople);
        
        //創(chuàng)建實例對象
        id peopleInstance = [[MyPeople alloc]init];
        
        [peopleInstance setValue:@"李明" forKey:@"name"];
        
        //獲取成員變量
        Ivar age = class_getInstanceVariable(MyPeople, "_age");
        object_setIvar(peopleInstance, age, @18);
        
        //發(fā)送消息
        objc_msgSend(peopleInstance,say,@"你好呀");
        
        //銷毀實例對象
        peopleInstance = nil;
        
        //當類或子類的實例存在，則不能銷毀類
        objc_disposeClassPair(MyPeople);
    }
    return 0;
}

tip：
默認會出現(xiàn)以下錯誤：
objc_msgSend()報錯Too many arguments to function call ,expected 0,have3
直接通過objc_msgSend(self, setter, value)是報錯污秆，說參數(shù)過多劈猪。
請這樣解決：
Build Setting–> Apple LLVM 7.0 – Preprocessing–> Enable Strict Checking of objc_msgSend Calls 改為 NO

通過runtime獲取類的相關信息(屬性、實例變量良拼、方法)

#import <Foundation/Foundation.h>

@interface People : NSObject{
    
    NSString* _nationality;

}

@property(nonatomic,copy)NSString* name;
@property(nonatomic,strong)NSNumber* age;

/**
 * 獲取所有屬性
 **/
-(NSDictionary*)getAllProperties;

/**
 * 獲取所有實例變量
 **/
-(NSDictionary*)getAllIvars;


/**
 * 獲取所有方法
 **/
-(NSDictionary*)getAllMethods;

@end

#import "People.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation People


-(NSDictionary *)getAllProperties{
    unsigned int count = 0;
    NSMutableDictionary* result = [@{} mutableCopy];
    objc_property_t* properties = class_copyPropertyList([self class], &count);
    for (NSUInteger i = 0; i<count; i++) {
        const char* propertyName = property_getName(properties[i]);
        NSString* name = [NSString stringWithUTF8String:propertyName];
        id propertyValue = [self valueForKey:name];
        if (propertyValue) {
            result[name] = propertyValue;
        }else{
            result[name] = @"value 不能為 nil";
        }
        
        
    }
    free(properties);

    return result;
}

-(NSDictionary *)getAllIvars{
    unsigned int count = 0;
    NSMutableDictionary* result = [@{} mutableCopy];
    Ivar* ivars = class_copyIvarList([self class], &count);
    for (NSUInteger i = 0; i<count; i++) {
        const char* ivarName = ivar_getName(ivars[i]);
        NSString* name = [NSString stringWithUTF8String:ivarName];
        id value = [self valueForKey:name];
        if (value) {
            result[name] = value;
        }else{
            result[name] = @"value 不能為 nil";
        }
    }
    free(ivars);
    return  result;
}

-(NSDictionary*)getAllMethods{
    unsigned int count = 0;
    NSMutableDictionary* result = [@{} mutableCopy];
    Method* methods = class_copyMethodList([self class], &count);
    for (NSUInteger i = 0; i<count; i++) {
        const char* methodName = sel_getName(method_getName(methods[i]));
        NSString* name = [NSString stringWithUTF8String:methodName];
        //獲取參數(shù)列表
        int args = method_getNumberOfArguments(methods[i]);
        result[name] = [NSString stringWithFormat:@"args count is %d",args-2 ];
    }
    free(methods);
    return result;
}

#import <Foundation/Foundation.h>
#import "People.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        People* p = [[People alloc]init];
        p.name = @"羅大錘";
        p.age = @(30);
        [p setValue:@"中國" forKey:@"nationality"];
        NSDictionary* properties = [p getAllProperties];
        NSDictionary* ivars = [p getAllIvars];
        NSDictionary* methods = [p getAllMethods];
        NSLog(@"屬性為：%@",properties);
        NSLog(@"實例變量：%@",ivars);
        NSLog(@"方法：%@",methods);
    }
    return 0;
}

打印結果：

2016-05-13 11:22:36.298 runtime 之 獲取類的相關信息(屬性岸霹、實例變量、方法)[2783:307932] 屬性為：{
    age = 30;
    name = "\U7f57\U5927\U9524";
}
2016-05-13 11:22:36.299 runtime 之 獲取類的相關信息(屬性将饺、實例變量贡避、方法)[2783:307932] 實例變量：{
    "_age" = 30;
    "_name" = "\U7f57\U5927\U9524";
    "_nationality" = "\U4e2d\U56fd";
}
2016-05-13 11:22:36.299 runtime 之 獲取類的相關信息(屬性、實例變量予弧、方法)[2783:307932] 方法：{
    ".cxx_destruct" = "args count is 0";
    age = "args count is 0";
    getAllIvars = "args count is 0";
    getAllMethods = "args count is 0";
    getAllProperties = "args count is 0";
    name = "args count is 0";
    "setAge:" = "args count is 1";
    "setName:" = "args count is 1";
}
Program ended with exit code: 0

通過Runtime給category添加屬性

#import "People.h"

typedef void(^CallBackSomething)();

@interface People (testCategory)

@property(nonatomic,copy)NSString* address;
@property(nonatomic,copy)CallBackSomething block;
@end

#import "People+testCategory.h"
#import <objc/runtime.h>
#import <objc/message.h>


@implementation People (testCategory)

-(void)setAddress:(NSString *)address{
    objc_setAssociatedObject(self, @selector(address), address, OBJC_ASSOCIATION_COPY_NONATOMIC);
}

-(NSString *)address{
    return objc_getAssociatedObject(self, @selector(address));
}

-(void)setBlock:(CallBackSomething)block{
    objc_setAssociatedObject(self, @selector(block), block, OBJC_ASSOCIATION_COPY_NONATOMIC);
}

-(CallBackSomething)block{
    return objc_getAssociatedObject(self, @selector(block));
}

@end

利用Runtime給對象歸檔和解檔

#import <Foundation/Foundation.h>

@interface People : NSObject<NSCoding>{
    
    NSString* _nationality;

}

@property(nonatomic,copy)NSString* name;
@property(nonatomic,strong)NSNumber* age;
@end

#import "People.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation People

//歸檔
-(void)encodeWithCoder:(NSCoder *)aCoder{
    unsigned int count = 0;
    Ivar* ivars = class_copyIvarList([self class],&count);
    for (NSUInteger i = 0; i<count; i++) {
        Ivar ivar = ivars[i];
        const char* name = ivar_getName(ivar);
        NSString* key = [NSString stringWithUTF8String:name];
        id value = [self valueForKey:key];
        [aCoder encodeObject:value forKey:key];
    }
    free(ivars);
}

//解檔
-(instancetype)initWithCoder:(NSCoder *)aDecoder{
    if (self = [super init]) {
        unsigned int count = 0;
        Ivar* ivars = class_copyIvarList([self class],&count);
        for (NSUInteger i = 0; i<count; i++) {
            Ivar ivar = ivars[i];
            const char* name = ivar_getName(ivar);
            NSString* key = [NSString stringWithUTF8String:name];
            id value = [aDecoder decodeObjectForKey:key];
            [self setValue:value forKey:key];
        }
        free(ivars);
    }
    return self;
}

@end

利用Runtime實現(xiàn)Model與字典互轉

#import <Foundation/Foundation.h>

@interface People : NSObject

@property(nonatomic,copy)NSString* name;
@property(nonatomic,strong)NSNumber* age;


/**
 * 字典 轉 Model
 **/
-(instancetype)initWithDictionary:(NSDictionary*) dict;

/**
 * Model轉換成字典
 **/
-(NSDictionary*)covertToDictionary;
@end

#import "People.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation People




-(instancetype)initWithDictionary:(NSDictionary *)dict{
    if (self = [super init]) {
        for (NSString* key in dict) {
            id val = dict[key];
            SEL setter = [self propertySetterByKey:key];
            if (setter) {
                objc_msgSend(self, setter,val);
            }
        }
    }
    return self;
}

-(NSDictionary *)covertToDictionary{
    unsigned int count = 0;
    objc_property_t* properties = class_copyPropertyList([self class], &count);
    
    if (count!=0) {
        NSMutableDictionary* result = [@{} mutableCopy];
        for (NSUInteger i = 0; i<count; i++) {
            const char * propertyName = property_getName(properties[i]);
            NSString* name = [NSString stringWithUTF8String:propertyName];
            
            SEL getter = [self propertyGetterByKey:name];
            if (getter) {
                id value = objc_msgSend(self, getter);
                if (value) {
                    result[name] = value;
                }else{
                    result[name] = @"value 為 nil";
                }
            }
        }
        free(properties);
        return result;
    }
    free(properties);
    return nil;
}

#pragma mark - 生成setter
-(SEL)propertySetterByKey:(NSString*)key{
    //key的首字母大寫
    NSString* propertySetterName = [NSString stringWithFormat:@"set%@:",key.capitalizedString];
    SEL setter = NSSelectorFromString(propertySetterName);
    if ([self respondsToSelector:setter]) {
        return setter;
    }
    return nil;
}

-(SEL)propertyGetterByKey:(NSString*)key{
    SEL getter = NSSelectorFromString(key);
    if ([self respondsToSelector:getter]) {
        return getter;
    }
    return nil;
}

@end

消息動態(tài)解析（一）

#import <Foundation/Foundation.h>

@interface People : NSObject

@property(nonatomic,copy)NSString* name;

/** m文件不實現(xiàn)方法刮吧，通過runtime動態(tài)添加方法
 *  通過resolveInstanceMethod：方法決定是否動態(tài)添加方法。
    如果返回Yes則通過class_addMethod動態(tài)添加方法掖蛤，消息得到處理杀捻，結束；如果返回No
 **/
-(void)sing;

@end

#import "People.h"
#import <objc/runtime.h>
#import <objc/message.h>


@implementation People

+(BOOL)resolveInstanceMethod:(SEL)sel{
    if ([NSStringFromSelector(sel) isEqualToString:@"sing"]) {
        class_addMethod([self class], sel, (IMP)otherIMP, "V@:");
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

void otherIMP(id self ,SEL cmd){
    NSLog(@"%@正在唱歌",((People*)self).name);
}

@end

#import <Foundation/Foundation.h>
#import "People.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        People* p = [[People alloc]init];
        p.name = @"張全蛋";
        [p sing];
    }
    return 0;
}

打印結果：

2016-05-13 11:24:16.905 runtime 之 消息動態(tài)解析(一)[2819:311517] 張全蛋正在唱歌
Program ended with exit code: 0

消息動態(tài)解析（二）

修改Bird唱歌方法的調用對象

#import <Foundation/Foundation.h>

@interface Bird : NSObject
@property(nonatomic,copy)NSString* name;
-(void)sing;
@end

#import "Bird.h"
#import "People.h"
@implementation Bird


//第一步蚓庭，不動態(tài)添加方法
+(BOOL)resolveInstanceMethod:(SEL)sel{
    return NO;
}

//第二步致讥，不指定備選對象響應sselector
-(id)forwardingTargetForSelector:(SEL)aSelector{
    
    return nil;
}

//第三步，返回方法簽名
-(NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    if ([NSStringFromSelector(aSelector) isEqualToString:@"sing"]) {
        return [NSMethodSignature signatureWithObjCTypes:"v@:"];
    }
    return [super methodSignatureForSelector:aSelector];
}

//第四部器赞，修改調用對象
-(void)forwardInvocation:(NSInvocation *)anInvocation{
    People* p = [[People alloc]init];
    p.name = @"張鐵柱";
    [anInvocation invokeWithTarget:p];
}

#import <Foundation/Foundation.h>
#import "Bird.h"
#import <objc/runtime.h>
#import <objc/message.h>
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Bird* b = [[Bird alloc]init];
        b.name = @"小鳥";
        [b sing];
    }
    return 0;
}

打印結果：

2016-05-13 11:29:58.335 runtime 之 消息動態(tài)解析(二)[2963:322829] 張鐵柱正在唱歌
Program ended with exit code: 0

消息動態(tài)解析（三）

修改Person唱歌方法的實現(xiàn)

#import <Foundation/Foundation.h>

@interface People : NSObject
-(void)sing;
@end

#import "People.h"

@implementation People

//不動態(tài)添加方法
+(BOOL)resolveInstanceMethod:(SEL)sel{
    return NO;
}

//不指定備選響應對象
-(id)forwardingTargetForSelector:(SEL)aSelector{
    return nil;
}

//返回方法簽名
-(NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    if ([NSStringFromSelector(aSelector) isEqualToString:@"sing"]) {
        return [NSMethodSignature signatureWithObjCTypes:"v@:"];
    }
    return [super methodSignatureForSelector:aSelector];
}

//修改調用方法
-(void)forwardInvocation:(NSInvocation *)anInvocation{
    [anInvocation setSelector:@selector(dance)];
    [anInvocation invokeWithTarget:self];
}

//若不實現(xiàn)forwardInvocation垢袱，則會調用此方法(可以注釋掉forwardInvocation方法來做實驗)
-(void)doesNotRecognizeSelector:(SEL)aSelector{
    NSLog(@"消息無法處理:%@",NSStringFromSelector(aSelector));
}

-(void)dance{
    NSLog(@"跳舞中");
}

@end

#import <Foundation/Foundation.h>
#import "People.h"
#import <objc/runtime.h>
#import <objc/message.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        People* p = [[People alloc]init];
        [p sing];
    }
    return 0;
}

打印結果：

2016-05-13 11:33:01.871 runtime 之 消息動態(tài)解析(三)[3073:329356] 跳舞中
Program ended with exit code: 0

以上demo地址

參考文章：
Objective-C Runtime 1小時入門教程
詳解Runtime運行時機制