Runtime effect (upper)

The runtime has four functions: 1. To send a message 2. Method of Exchange 3. Adding methods dynamically 4. Adding attributes to the Category 5. Dictionary to model

Function One: Send Message

• The essence of a method invocation is to have the object send a message.
• Objc_msgsend, only objects can send messages, so start with OBJC.
• Use 消息机制 premise, must import #import <objc/message.h>
• Message mechanism simple to use
• CLANG-REWRITE-OBJC main.m View Final generated code

    // 创建person对象    Person *p = [[Person alloc] init];    // 调用对象方法    [p eat];    // 本质：让对象发送消息    objc_msgSend(p, @selector(eat));    // 调用类方法的方式：两种    // 第一种通过类名调用    [Person eat];    // 第二种通过类对象调用    [[Person class] eat];    // 用类名调用类方法，底层会自动把类名转换成类对象调用    // 本质：让类对象发送消息    objc_msgSend([Person class], @selector(eat));

Function Two: Exchange method

• Development of the use of the scene: The system's own method is not enough, to the system's own method to extend some functions, and maintain the original function.
• Method One: Inherit the class of the system, overriding the method.
• Mode two: Use runtime, Exchange method.

@implementation viewcontroller-(void) viewdidload {[Super viewdidload];    Additional setup after loading the view, typically from a nib.    Requirements: To provide functionality to the Imagenamed method, each time the picture is loaded to determine whether the tablet is loaded successfully.    Step one: First make a classification, define a can load the picture and can print method + (Instancetype) Imagewithname: (NSString *) name;    Step two: Exchange imagenamed and Imagewithname implementation, you can call Imagewithname, indirectly invoke the implementation of Imagewithname. UIImage *image = [UIImage imagenamed:@ "123"];} @end @implementation UIImage (Image)//load classification to memory when Call + (void) load{//Exchange method//Get Imagewithname method address methods Imagewithna    me = Class_getclassmethod (self, @selector (imagewithname:));    Get Imagewithname method Address ImageName = Class_getclassmethod (self, @selector (imagenamed:)); Interchange method address, equivalent to interchange implementation mode Method_exchangeimplementations (Imagewithname, imageName);} The system method imagenamed cannot be overridden in the classification, because the function of the system will be overwritten, and the classification cannot be called super.//can both load the picture and print + (Instancetype) Imagewithname: (NSString *) name    {//Call imagewithname here, equivalent to calling imagename UIImage *image = [self imagewithname:name];   if (image = = nil) {     NSLog (@ "Load empty picture"); } return image; @end

Function Three: dynamic addition method

• Development Use Scenario: If a class method is very many, load the class to memory is also more expensive, need to give each method to generate a mapping table, you can use the dynamic to a class, add methods to solve.
• Classic Interview questions: There is no use of performselector, in fact, I would like to ask you have not dynamically added methods.
• Simple to use

@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.    Person *p = [[Person alloc] init];    // 默认person，没有实现eat方法，可以通过performSelector调用，但是会报错。    // 动态添加方法就不会报错    [p performSelector:@selector(eat)];}@end@implementation Person// void(*)()// 默认方法都有两个隐式参数，void eat(id self,SEL sel){    NSLog(@"%@ %@",self,NSStringFromSelector(sel));}// 当一个对象调用未实现的方法，会调用这个方法处理,并且会把对应的方法列表传过来.// 刚好可以用来判断，未实现的方法是不是我们想要动态添加的方法+ (BOOL)resolveInstanceMethod:(SEL)sel{    if (sel == @selector(eat)) {        // 动态添加eat方法        // 第一个参数：给哪个类添加方法        // 第二个参数：添加方法的方法编号        // 第三个参数：添加方法的函数实现（函数地址）        // 第四个参数：函数的类型，(返回值+参数类型) v:void @:对象->self :表示SEL->_cmd        class_addMethod(self, @selector(eat), eat, "[email protected]:");    }    return [super resolveInstanceMethod:sel];}@end

Runtime effect (upper)