runtime运行时常用方法引入头文件#import <objc/runtime.h> 常见runtime api ob

引入头文件#import <objc/runtime.h>

常见runtime api

object_getClass 获取class
- Class objClass = object_getClass([NSObject alloc]);
class_getName(Class _Nullable cls) 获取类名传入class
- const char *className = class_getName(objClass);
objc_getMetaClass(const char * _Nonnull name) 获取元类传入class名
- Class metaClass = objc_getMetaClass(className);
class_getInstanceMethod(Class _Nullable cls, SEL _Nonnull name) 获取实例方法
- Method instanceMethod = class_getInstanceMethod(objClass, @selector(xxInstanceMethod));

class_getClassMethod(Class _Nullable cls, SEL _Nonnull name) //获取类方法

Method classMethod = class_getClassMethod(metaClass, @selector(xxClassMethod));
元类也返回类方法，和类方法地址一样

源码如下：

Method class_getClassMethod(Class cls, SEL sel)
{
    if (!cls  ||  !sel) return nil;
    return class_getInstanceMethod(cls->getMeta(), sel);
}

Class getMeta() {
    if (isMetaClassMaybeUnrealized()) return (Class)this;//判断是元类就返回 避免查询递归
    else return this->ISA();
}

SEL method_getName(Method m) 从Method获取sel名

Method class_copyMethodList(Class cls, unsigned int outCount) //获取类cls的方法

示例：

 //打印Class pClass的实例方法
 void objc_copyMethodList(Class pClass){
      unsigned int count = 0;
      Method *methods = class_copyMethodList(pClass, &count);
      NSLog(@"----------------");           
      NSLog(@"%s",__func__);
      for (unsigned int i=0; i < count; i++) {
          Method const method = methods[i];
          //获取方法名
          NSString *key = NSStringFromSelector(method_getName(method));
          NSLog(@"%@实例方法: %@", pClass,key);
      }
      free(methods);
 }

IMP class_getMethodImplementation(Class cls, SEL sel) 获取方法实现指针

Class pClass = object_getClass([NSObject alloc]);IMP imp = class_getMethodImplementation(pClass, @selector(xxInstanceMethod));

源码：

IMP class_getMethodImplementation(Class cls, SEL sel)
{
    IMP imp;
    if (!cls  ||  !sel) return nil;
    ...
    imp = lookUpImpOrNilTryCache(nil, sel, cls, LOOKUP_INITIALIZE | LOOKUP_RESOLVER);

    // Translate forwarding function to C-callable external version
    if (!imp) { //如果找不到（没有这个方法或者只声明未实现）就会找消息转发_objc_msgForward
        return _objc_msgForward;
    }

    return imp;
}

const char *ivar_getName(Ivar ivar) 获取实例变量名
Ivar *class_copyIvarList(Class cls, unsigned int *outCount) 获取成员变量列表

objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount) 获取属性列表

示例：

//获取成员变量和属性
void objc_copyIvar_copyProperies(Class pClass){
   unsigned int count = 0;
   Ivar *ivars = class_copyIvarList(pClass, &count);
   for (unsigned int i=0; i < count; i++) {
       Ivar const ivar = ivars[i];
       //获取实例变量名
       const char*cName = ivar_getName(ivar);
       NSString *ivarName = [NSString stringWithUTF8String:cName];
       LGLog(@"class_copyIvarList:%@",ivarName);
   }
   free(ivars);

   unsigned int pCount = 0;
   objc_property_t *properties = class_copyPropertyList(pClass, &pCount);
   for (unsigned int i=0; i < pCount; i++) {
       objc_property_t const property = properties[i];
       //获取属性名
       NSString *propertyName = [NSString stringWithUTF8String:property_getName(property)];
       //获取属性值
       LGLog(@"class_copyProperiesList:%@",propertyName);
   }
   free(properties);
}

const char *ivar_getTypeEncoding(Ivar ivar) 获取对应的编码。详细参见Type Encodings
const char *property_getName(objc_property_t prop) 获取属性名
const char *property_getAttributes(objc_property_t prop) 获取属性真实类型
- 举例：
```
//Person.h
@property (nonatomic, copy) NSString *nickName;

//使用
Class pClass = Person.class;
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList(pClass, &outCount);
for (i = 0; i < outCount; i++) {
    objc_property_t property = properties[i];
    fprintf(stdout, "%s %s\n", property_getName(property), property_getAttributes(property));
}
```
  打印：nickName T@"NSString",C,N,V_nickName
  说明：T: 在大写 T 后面是放的是该属性的数据类型 NSString;
  C : copy;
  N : nonatomic;
  V: 在大写 V 后面放的是该属性的变量名称(因为我们知道 @property 实际上只是为我们编写好了 getter 和 setter 方法，并创建一个以下划线开头的变量_nickName);
  详细参见官方文档.
SEL sel_registerName(const char * _Nonnull str) //获取sel