In layman's language Runtime (a): acquaintance

Runtime series

Layman Runtime (a): acquaintance
layman Runtime (2): The data structure
layman Runtime (III): messaging
layman Runtime (IV): The nature of super
layman Runtime (e): a particular application
layman Runtime (VI): interview questions related

Runtime Introduction

• Runtime with a C、汇编run library prepared, comprising the API of a number of C language, a lot of dynamic package related functions;
• Objective-C is a dynamic language runtime, allowing many operations to further defer the program is running. OCThe dynamics is Runtimesupported and implemented, Rumtimeis its core;
• We usually write OCthe code, the underlying are converted to Runtime APImake the call.

Objective-C is a dynamic language runtime

What is a compile-time and run-time?

• Compilation: Compiler program code into computer language can be identified, for only a few simple syntax check;
• Runtime: Code run up, is loaded into memory at this time if an error causes the program to crash. Such as the classic unrecognized selector send to instance/classCrash: .

Language differences with the dynamic language runtime compile time?

• Language compilation: a function at compile time resolution;
• Dynamic Language Runtime: The function resolutions deferred until runtime.

For example

For NSString *string = [[NSMutableArray alloc]init];

• Compile-time: time compiler type checking, since a given NSStringtype is a pointer assignment NSMutableArrayobject, the compiler will give a warning type mismatch. But the compiler will stringas NSStringexamples, the stringobject calls the NSStringmethod, the compiler without any problems, and call NSMutableArraythe method, the compiler will direct error.
• Runtime: Because stringactually pointing to a NSMutableArraytarget, NSMutableArraythe object is no stringByAppendingString：method, resulting in Crash: unrecognized selector send to instance.

    NSString *string = [[NSMutableArray alloc]init];  //⚠️Incompatible pointer types initializing 'NSString *' with an expression of type 'NSMutableArray *'
    [string stringByAppendingString:@"abc"];
    [string addObject:@"abc"];  //❌No visible @interface For 'NSString' declares the selector 'addObject:'

There are two versions Runtime

• Legacy (earlier), the corresponding programming interface: Objective-C 1.0, is applied 32-bit programs on OS X desktop;
• AND ECONOMICS (modern version), the corresponding programming interface: in Objective-C 2.0 , is applied iPhone applications and 64-bit programs on OS X v10.5 and later.

Objective-C Runtime program to interact with the system in three different levels

• By Objective-C source code;
• Methods Foundation framework NSObject class definition, such as:

// 根据 instance 对象或者类名获得一个 class 对象
- (Class)class
+ (Class)class
// 判断当前 instance/class 对象的 isa 指向是不是 class/meta-class 对象或者它的子类类型
- (BOOL)isKindOfClass:(Class)cls
+ (BOOL)isKindOfClass:(Class)cls
// 判断当前 instance/class 对象的 isa 指向是不是 class/meta-class 对象类型
- (BOOL)isMemberOfClass:(Class)cls
+ (BOOL)isMemberOfClass:(Class)cls
// 判断对象是否可以接收特定消息
- (BOOL)respondsToSelector:(SEL)sel
+ (BOOL)respondsToSelector:(SEL)sel
// 判断对象是否实现了特定协议中定义的方法
- (BOOL)conformsToProtocol:(Protocol *)protocol
+ (BOOL)conformsToProtocol:(Protocol *)protocol
// 可以根据一个 SEL，得到该方法的 IMP
- (IMP)methodForSelector:(SEL)sel
+ (IMP)methodForSelector:(SEL)sel

• By directly calling Runtime functions , such as:

Or related

// 动态创建一对类和元类（参数：父类，类名，额外的内存空间）
Class objc_allocateClassPair(Class superclass, const char *name, size_t extraBytes)
// 注册一对类和元类（要在类注册之前添加成员变量）
void objc_registerClassPair(Class cls) 
// 销毁一对类和元类
void objc_disposeClassPair(Class cls)
// 获取 isa 指向的 Class
Class object_getClass(id obj)
// 设置 isa 指向的 Class
Class object_setClass(id obj, Class cls)
// 判断一个 OC 对象是否为 Class
BOOL object_isClass(id obj)
// 判断一个 Class 是否为元类
BOOL class_isMetaClass(Class cls)
// 获取父类
Class class_getSuperclass(Class cls)

Member variable

// 获取一个实例变量信息
Ivar class_getInstanceVariable(Class cls, const char *name)
// 拷贝实例变量列表（最后需要调用 free 释放）
Ivar *class_copyIvarList(Class cls, unsigned int *outCount)
// 设置和获取成员变量的值
void object_setIvar(id obj, Ivar ivar, id value)
id object_getIvar(id obj, Ivar ivar)
// 动态添加成员变量（已经注册的类是不能动态添加成员变量的）
BOOL class_addIvar(Class cls, const char * name, size_t size, uint8_t alignment, const char * types)
// 获取成员变量的相关信息
const char *ivar_getName(Ivar v)
const char *ivar_getTypeEncoding(Ivar v)

Property related

// 获取一个属性
objc_property_t class_getProperty(Class cls, const char *name)
// 拷贝属性列表（最后需要调用 free 释放）
objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)
// 动态添加属性
BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)
// 动态替换属性
void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes, unsigned int attributeCount)
// 获取属性的一些信息
const char *property_getName(objc_property_t property)
const char *property_getAttributes(objc_property_t property)

RELATED

// 获得一个实例方法、类方法
Method class_getInstanceMethod(Class cls, SEL name)
Method class_getClassMethod(Class cls, SEL name)
// 方法实现相关操作
IMP class_getMethodImplementation(Class cls, SEL name) 
IMP method_setImplementation(Method m, IMP imp)
void method_exchangeImplementations(Method m1, Method m2) 
// 拷贝方法列表（最后需要调用 free 释放）
Method *class_copyMethodList(Class cls, unsigned int *outCount)
// 动态添加方法
BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types)
// 动态替换方法
IMP class_replaceMethod(Class cls, SEL name, IMP imp, const char *types)
// 获取方法的相关信息（带有 copy 的需要调用 free 去释放）
SEL method_getName(Method m)
IMP method_getImplementation(Method m)
const char *method_getTypeEncoding(Method m)
unsigned int method_getNumberOfArguments(Method m)
char *method_copyReturnType(Method m)
char *method_copyArgumentType(Method m, unsigned int index)
// 选择器相关
const char *sel_getName(SEL sel)
SEL sel_registerName(const char *str)
// 用 block 作为方法实现
IMP imp_implementationWithBlock(id block)
id imp_getBlock(IMP anImp)
BOOL imp_removeBlock(IMP anImp)

Related objects associated
Portal: OC - Association associated objects

// 添加关联对象
void objc_setAssociatedObject(id object, const void * key, id value, objc_AssociationPolicy policy)
// 获得关联对象
id objc_getAssociatedObject(id object, const void * key)
// 移除指定 object 的所有关联对象
void objc_removeAssociatedObjects(id object)

What are Runtime application?

• Using associated object (the AssociatedObject) to add an attribute classification
• All members of the class variable traverse (modified textfield placeholder text color, and turn the dictionary model, automatic archiving solution file)
• Implemented method of switching (switching system intercept method)
• Message forwarding mechanism using the method to solve unusual problems can not be found
• …

Related Links

Apple maintained Runtime open source
GNU open source maintained Runtime
Apple's official documentation Runtime