iOS runtime基本用法

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一. 改变实例变量的值 (KVC/MJExtension都是通过这种方式来实现的)

• 添加Person类, 只添加了name属性, 这里跳过实现文件

  @interface Person : NSObject
  
  @property (copy, nonatomic) NSString *name;
  
  @end
  

• 创建Person类型的实例对象

  self.person = [Person new];
  self.person.name = @"homer";
  NSLog(@"%@", self.person.name);
  

• 添加方法, 修改name属性的值

  - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
      /// 获取变量个数
      unsigned int count = 0;
      /// 获取所有的实例变量
      Ivar *ivar = class_copyIvarList([self.person class], &count);
      /// 遍历
      for (int i = 0; i < count; i++) {
          /// 实例变量
          Ivar var = ivar[i];
          /// 实例变量名字
          const char *varName = ivar_getName(var);
          /// 转化一下
          NSString *name = [NSString stringWithUTF8String:varName];
          
          if ([name isEqualToString:@"_name"]) {
              object_setIvar(self.person, var, @"lynn");
              break;
          }
      }
      NSLog(@"%@", self.person.name);
  }
  

• 控制台输出,显示修改成功

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二. 方法交换(常用来hock/埋点等)

• 在Person中新增2个方法

  - (void)firstMethod {
      NSLog(@"1st method has been called");
  }
  
  - (void)secondMethod {
      NSLog(@"2nd method has been called");
  }
  

• 实现方法交换

  - (void)exchangeMethod {
      /// 获取方法
      Method m1 = class_getInstanceMethod([self.person class], @selector(firstMethod));
      Method m2 = class_getInstanceMethod([self.person class], @selector(secondMethod));
      
      /// 交换方法
      method_exchangeImplementations(m1, m2);
  }
  

• 分别在交换前后调用firstMethod和secondMethod, 查看控制台输出

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三. 动态添加方法

• 添加方法

  - (void)addMethod {
      /// "v@:@"      v表示void, @表示id类型, :表示SEL
      class_addMethod([self.person class], @selector(run:), (IMP)run, "v@:@");
  }
  
  void run(id self, SEL _cmd, NSString *miles) {
      NSLog(@"Tome run %@ miles", miles);
  }
  
  - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
      [self addMethod];
      
      if ([self.person respondsToSelector:@selector(run:)]) {
          [self.person performSelector:@selector(run:) withObject:@"1"];
      } else {
          NSLog(@"Method named run: is not been defined!");
      }
  }
  

• 查看输出

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四. 使用关联属性给类型添加属性

• 给Person类添加nick属性

  @property (copy, nonatomic) NSString *name;
  
  - (void)firstMethod {
      NSLog(@"1st method has been called");
  }
  
  - (void)secondMethod {
      NSLog(@"2nd method has been called");
  }
  

• 调用属性

  - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
      self.person.nick = @"Homer Lynn";
      NSLog(@"%@", self.person.nick);
  }
  

• 查看输出

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