修改实例方法，增加新的实例方法

修改实例方法

import Foundation
import UIKit

class Demo:NSObject{
    dynamic func test(msg:String){
        print(msg)
    }
    
    class func test1(msg:String){
        print(msg)
    }
}
let sel = #selector(Demo.test(msg:))

/// 获取test(msg:)的方法
let method:Method = class_getInstanceMethod(Demo.self, sel)
/// 获取方法实现体的指针
let oldIMP:IMP = method_getImplementation(method)

// 把方法体指针转成具体的block
typealias OldBlockType = @convention(c) (Demo,Selector,String)->Void


let oldBlock = unsafeBitCast(oldIMP, to: OldBlockType.self)

// 调用
//oldBlock(Demo(), sel, "调用方法。")

// 参数方法要把类名带上，方法名不用带。带了出错。
let newBlock:@convention(block)(Demo,String)->Void = {(demo,msg) in
    print("before")
    oldBlock(demo, sel, msg)
    print("after")
}
let newIMP = imp_implementationWithBlock(unsafeBitCast(newBlock, to: AnyObject.self))

method_setImplementation(method, newIMP)

Demo().test(msg: "jjj")

//结果
/*
before
jjj
after
*/

增加新的实例方法

import Foundation
import UIKit


class Demo:NSObject{
    dynamic func test(msg:String){
        print(msg)
    }
    
    class func test1(msg:String){
        print(msg)
    }
}

//方法体
typealias NewBlock = @convention(block)(Demo,Selector,String)->Void
let block:NewBlock = { (demo,sel,msg) in
    print(msg)
}

//方法引用 IMP
let imp = imp_implementationWithBlock(unsafeBitCast(block, to: AnyObject.self))

//方法选择器
let sel = Selector(("newFunc"))

//向类里增加方法
class_addMethod(Demo.self, sel, imp, "v@:")
//调用新的方法
Demo().perform(sel,with: "新增加了一个方法。")

/*
 新增加了一个方法。
 */