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runtime那些事儿(消息机制)

runtime那些事儿(消息机制)

本文是投稿文章,作者: HenryCheng

一、关于runtime

之前在项目中有遇到过用runtime解决改变全局字体的问题,所以再一次感受到了runtime黑魔法的强大,趁现在有机会分享一下对runtime的一些理解。在对象调用方法是Objective-C中经常使用的功能,也就是消息的传递,而Objective-C是C的超集,所以和C不同的是,Objective-C使用的是动态绑定,也就是runtime。Objective-C的消息传递和消息机制也就不多说了,今天主要说的是动态方法,也就是函数的调用。

二、相关的几个函数

下面一张图详细的概括了每个函数调用的先后以及执行的前提

runtime那些事儿(消息机制)

消息传递函数的调用

1.对象在收到无法解读的消息后,首先会调用所属类的

+ (BOOL)resolveInstanceMethod:(SEL)sel

这个方法在运行时,没有找到SEL的IML时就会执行。这个函数是给类利用class_addMethod添加函数的机会。根据文档,如果实现了添加函数代码则返回YES,未实现返回NO。举个例子,新建了一个工程,首先我在ViewController这个类中执行doSomething1这个方法,代码如下

// //  ViewController.m //  RuntimeTest1 // //  Created by HenryCheng on 15/12/24. //  Copyright ?(版权符号) 2015年 www.igancao.com  All rights reserved. //  #import "ViewController.h"  @interface ViewController ()  @end  @implementation ViewController  - (void)viewDidLoad {     [super viewDidLoad];     [self performSelector:@selector(doSomething)]; }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. }  @end

运行结果

**2015-12-24 10:35:37.726 RuntimeTest1[1877:337842] -[ViewController doSomething]: unrecognized selector sent to instance 0x7fe9f3736680** **2015-12-24 10:35:37.729 RuntimeTest1[1877:337842] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController doSomething]: unrecognized selector sent to instance 0x7fe9f3736680'** ***** First throw call stack:**

不出意外,程序崩溃,因为没有找到doSomething这个方法,下面我们在里面实现 + (BOOL)resolveInstanceMethod:(SEL)sel这个方法,并且判断如果SEL 是doSomething那就输出add method here

// //  ViewController.m //  RuntimeTest1 // //  Created by HenryCheng on 15/12/24. //  Copyright ?(版权符号) 2015年 www.igancao.com All rights reserved. //  #import "ViewController.h"  @interface ViewController ()  @end  @implementation ViewController  - (void)viewDidLoad {     [super viewDidLoad];     [self performSelector:@selector(doSomething)]; }  + (BOOL)resolveInstanceMethod:(SEL)sel {     if (sel == @selector(doSomething)) {         NSLog(@"add method here");         return YES;     }     return [super resolveInstanceMethod:sel]; }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. }  @end

继续运行,然后看到log

**2015-12-24 10:47:24.687 RuntimeTest1[2007:382077] add method here** **2015-12-24 10:47:24.687 RuntimeTest1[2007:382077] -[ViewController doSomething]: unrecognized selector sent to instance 0x7f9568c331f0** **2015-12-24 10:47:24.690 RuntimeTest1[2007:382077] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController doSomething]: unrecognized selector sent to instance 0x7f9568c331f0'** ***** First throw call stack:**

可以看到程序依然是崩溃了,但是我们可以看到输出了add method here,这说明我们 + (BOOL)resolveInstanceMethod:(SEL)sel这个方法执行了,并进入了判断,所以,在这儿,我们可以做一下操作,使这个方法得到相应,不至于走到最后- (void)doesNotRecognizeSelector:(SEL)aSelector这个方法中而崩掉了,接下来,我么继续操作,如下

// //  ViewController.m //  RuntimeTest1 // //  Created by HenryCheng on 15/12/24. //  Copyright ?(版权符号) 2015年 www.igancao.com All rights reserved. //  #import "ViewController.h"  #import [objc/runtime.h](因识别问题,此处将尖括号改为方括号)  @interface ViewController ()  @end  @implementation ViewController  - (void)viewDidLoad {     [super viewDidLoad];     [self performSelector:@selector(doSomething)]; }  + (BOOL)resolveInstanceMethod:(SEL)sel {     if (sel == @selector(doSomething)) {         NSLog(@"add method here");         class_addMethod([self class], sel, (IMP)dynamicMethodIMP, "v@:");         return YES;     }     return [super resolveInstanceMethod:sel]; } void dynamicMethodIMP (id self, SEL _cmd) {     NSLog(@"doSomething SEL"); }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. }  @end

导入了 并且在+ (BOOL)resolveInstanceMethod:(SEL)sel中执行了class_addMethod这个方法,然后定义了一个void dynamicMethodIMP (id self, SEL _cmd)这个函数,运行工程,看log

**2015-12-24 11:45:11.934 RuntimeTest1[2284:478571] add method here** **2015-12-24 11:45:11.934 RuntimeTest1[2284:478571] doSomething SEL**

这时候我们发现,程序并没有崩溃,而且还输出了doSomething SEL,这时候就说明我们已经通过runtime成功的向我们这个类中添加了一个方法。关于class_addMethod这个方法,是这样定义的

OBJC_EXPORT BOOL class_addMethod(Class cls, SEL name, IMP imp,  const char *types)
  • cls   在这个类中添加方法,也就是方法所添加的类

  • name  方法名,这个可以随便起的

  • imp   实现这个方法的函数

  • types 定义该数返回值类型和参数类型的字符串,这里比如"v@:",其中v就是void,带表返回类型就是空,@代表参数,这里指的是id(self),这里:指的是方法SEL(_cmd),比如我再定义一个函数

int newMethod (id self, SEL _cmd, NSString *str) {    return 100; }

那么添加这个函数的方法就应该是ass_addMethod([self class], @selector(newMethod), (IMP)newMethod, "i@:@");

2.如果在+ (BOOL)resolveInstanceMethod:(SEL)sel中没有找到或者添加方法

消息继续往下传递到- (id)forwardingTargetForSelector:(SEL)aSelector看看是不是有对象可以执行这个方法,我们来重新建个工程,然后新建一个叫SecondViewController的类,里面有一个- (void)secondVCMethod方法,如下

// //  SecondViewController.m //  RuntimeTest2 // //  Created by HenryCheng on 15/12/24. //  Copyright ?(版权符号) 2015年  www.igancao.com All rights reserved. //  #import "SecondViewController.h"  @interface SecondViewController ()  @end  @implementation SecondViewController  - (void)viewDidLoad {     [super viewDidLoad];     // Do any additional setup after loading the view. }  - (void)secondVCMethod {     NSLog(@"This is secondVC method !"); }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. }  /* #pragma mark - Navigation  // In a storyboard-based application, you will often want to do a little preparation before navigation - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {     // Get the new view controller using [segue destinationViewController].     // Pass the selected object to the new view controller. } */  @end

工程结构应该是这样的

runtime那些事儿(消息机制)

工程目录图

现在我想在ViewController中调用- (void)secondVCMethod这个方法,我们知道ViewController和SecondViewController并无继承关系,按照正常的步骤去做程序肯定会因为在ViewController找不到- (void)secondVCMethod这个方法而直接崩溃的

// //  ViewController.m //  RuntimeTest2 // //  Created by HenryCheng on 15/12/24. //  Copyright ?(版权符号) 2015年 www.igancao.com  All rights reserved. //  #import "ViewController.h" #import @interface ViewController ()  @end  @implementation ViewController  - (void)viewDidLoad {     [super viewDidLoad];      [self performSelector:@selector(secondVCMethod)]; }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. }  @end

运行结果

**2015-12-24 13:54:44.314 RuntimeTest2[3164:835814] -[ViewController secondVCMethod]: unrecognized selector sent to instance 0x7fc3a8535c10** **2015-12-24 13:54:44.317 RuntimeTest2[3164:835814] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController secondVCMethod]: unrecognized selector sent to instance 0x7fc3a8535c10'** ***** First throw call stack:**

现在我们来处理一下这个消息,如下

// //  ViewController.m //  RuntimeTest2 // //  Created by HenryCheng on 15/12/24. //  Copyright ?(版权符号) 2015年 www.igancao.com All rights reserved. //  #import "ViewController.h" #import @interface ViewController ()  @end  @implementation ViewController  - (void)viewDidLoad {     [super viewDidLoad];      [self performSelector:@selector(secondVCMethod)]; }  - (id)forwardingTargetForSelector:(SEL)aSelector {     Class class = NSClassFromString(@"SecondViewController");     UIViewController *vc = class.new;     if (aSelector == NSSelectorFromString(@"secondVCMethod")) {         NSLog(@"secondVC do this !");         return vc;     }          return nil; }  + (BOOL)resolveInstanceMethod:(SEL)sel {      return [super resolveInstanceMethod:sel]; }  - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning];     // Dispose of any resources that can be recreated. } @end

运行结果

**2015-12-24 14:00:34.168 RuntimeTest2[3284:870957] secondVC do this !** **2015-12-24 14:00:34.169 RuntimeTest2[3284:870957] This is secondVC method !**

我们会发现- (void)secondVCMethod这个方法执行了,程序也并没有崩溃,原因就是在这一步

- (id)forwardingTargetForSelector:(SEL)aSelector {     Class class = NSClassFromString(@"SecondViewController");     UIViewController *vc = class.new;     if (aSelector == NSSelectorFromString(@"secondVCMethod")) {         NSLog(@"secondVC do this !");         return vc;     }          return nil; }

在没有找到- (void)secondVCMethod这个方法的时候,消息继续传递,直到- (id)forwardingTargetForSelector:(SEL)aSelector,然后我在里面创建了一个SecondViewController的对象,并且判断如过有这个方法,就返回SecondViewController的对象。这个函数就是消息的转发,在这儿我们成功的把消息传给了SecondViewController,然后让它来执行,所以就执行了那个方法。同时,也相当于完成了一个多继承!

三、最后一点

当然,还有好几个函数,在上面那张图里面已经清晰的表达了,有兴趣的可以自己试试,看看消息的传递顺序到底是怎么样的。上面提到的这些知识runtime的冰山一角,runtime黑魔法的强大远不止于此,比如方法的调配(Method Swizzling)等,在项目实战中还是很有用的,后面有时间会再介绍.

参考

原文  http://www.cocoachina.com/ios/20160302/15494.html
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