消息转发机制共分为3大步骤：

1.Method resolution 方法解析处理阶段

2.Fast forwarding 快速转发阶段

3.Normal forwarding 常规转发阶段

消息转发机制

动态方法解析

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
NS_ASSUME_NONNULL_BEGIN

@interface Presson : NSObject

-(void)sendMessage:(NSString *)message;

@end

#import "Presson.h"

@implementation Presson

void sendMessage(id self, SEL _cmd, NSString *msg){
    NSLog(@"----%@",msg);
}

+ (BOOL)resolveInstanceMethod:(SEL)sel
{
    // 1配置方法
    NSString *methodNme = NSStringFromSelector(sel);
    if ([methodNme isEqualToString:@"sendMessage:"]) {
        return  class_addMethod(self, sel, (IMP)sendMessage, "v@:@");
    }
    return NO;
}

@end

#import "ViewController.h"
#import "Presson.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    [[Presson new]sendMessage:@"helloworld"];
}


@end

快速转发

//快速转发

//-(id)forwardingTargetForSelector:(SEL)aSelector{
//    // 1配置方法
//    NSString *methodNme = NSStringFromSelector(aSelector);
//    if ([methodNme isEqualToString:@"sendMessage:"]) {
//        return  [SpareWheel new];
//    }
//    return [super forwardingTargetForSelector:aSelector];
//}

慢速转发

//1.方法签名
//2.消息转发
-(NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    NSString *methodNme = NSStringFromSelector(aSelector);
    if ([methodNme isEqualToString:@"sendMessage:"]) {
        return  [NSMethodSignature signatureWithObjCTypes:"v@:@"];
    }
    return [super forwardingTargetForSelector:aSelector];
}

-(void)forwardInvocation:(NSInvocation *)anInvocation{
//    SEL sel = [anInvocation selector];
//    SpareWheel *tempObj = [SpareWheel new];
//    if ([tempObj respondsToSelector:sel]) {
//        [anInvocation invokeWithTarget:tempObj];
//    }else{
//        [super forwardInvocation:anInvocation];
//    }
    [super forwardInvocation:anInvocation];
}

-(void)doesNotRecognizeSelector:(SEL)aSelector
{
    NSLog(@"找不到方法");
}