通过runtime修改系统默认的字体、颜色等等

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这个是我写的一个demo，你们可以去看看，欢迎star https://github.com/mafangchao/MCChangeLabelFont-OC/tree/master 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

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

#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

#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

#import "ViewController.h"

#import objc/runtime.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"); 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

#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

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

#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

#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.

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