Runtime mechanism principle and application

First, we first understand the runtime implementation mechanism and role

1. What is the mechanism of runtime implementation?

Runtime is a relatively low level of pure C language API, belongs to 1 C language Library, contains a lot of the underlying C language API.
In the OC code that we usually write, the program runs the process, in fact, it turns into the runtime's C language code, runtime is OC's behind-the-scenes workers
For example, in the following method of creating an object,
Example:
Oc:
[[Mjperson alloc] init]
Runtime:
Objc_msgsend (Objc_msgsend ("Mjperson", "Alloc"), "Init")

2. What is runtime used for?? Where do you use them?

Runtime is the bottom of the OC, you can do some very low-level operations (with OC things can not be achieved, not good implementation)

(1) Dynamically create a class during program run (for example, KVO implementation)

(2) Dynamically add properties \ Methods to a class, modify property values \ Methods during program run

(3) Traverse all member variables (attributes) of a class \ All methods

For example: We need to archive the properties of a class when the properties are particularly large, when we will write a lot of corresponding code, but if you use the runtime can be set dynamically!

• For example, the PYPerson.h file looks like this

  Import

@interface Pyperson:nsobject
@property (nonatomic, assign) int age;
@property (nonatomic, assign) int height;
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) int age2;
@property (nonatomic, assign) int height2;
@property (nonatomic, assign) int age3;
@property (nonatomic, assign) int height3;
@property (nonatomic, assign) int age4;
@property (nonatomic, assign) int height4;

@end

and the contents of the PYPERSON.M implementation file are as follows

<!-- lang: cpp -->#import "PYPerson.h"

Import

@implementation Pyperson

• (void) Encodewithcoder: (Nscoder ) encoder
  {
  unsigned int count = 0;
  Ivar ivars = Class_copyivarlist ([Pyperson class], &count);

  for (int i = 0; i<count; i++) {

  // 取出i位置对应的成员变量Ivar ivar = ivars[i];// 查看成员变量const char *name = ivar_getName(ivar);// 归档NSString *key = [NSString stringWithUTF8String:name];id value = [self valueForKey:key];[encoder encodeObject:value forKey:key];

  }

  Free (ivars);
  }

• (ID) Initwithcoder: (Nscoder *) decoder
  {
  if (self = [super init]) {

   unsigned int count = Span class= "Hljs-number" >0;ivar *ivars = Class_copyivarlist ([Pyperson class], &count); for (int i = 0; i<count; i++) { Span class= "hljs-comment" >//remove the member variable corresponding to the i position Ivar Ivar = ivars[i]; //View member variables const char *name = Ivar_ GetName (Ivar); //archive nsstring *key = [NSString Stringwithutf8string:name]; id value = [Decoder decodeobjectforkey:key]; //set to member variable body [self setvalue:value Forkey:key];} Free (ivars);                

  }
  return self;
  }

@end

So we can see the case of the archive and the file is actually written by runtime.

Learning, the runtime mechanism must first understand the following questions
1 Related header files and functions
1> header File

• 
  With the header file, we can view the various methods in the runtime!

2> related applications

• Nscoding (archive and file, use Runtime to traverse all properties of Model objects)
• Dictionary –> model (use Runtime to traverse all properties of the model object, remove the corresponding value from the dictionary based on the property name, set to the properties of the model)
• KVO (using runtime to generate a class dynamically)
• For packaging frames (how to change them)
  That's the way we use the runtime mechanism.

3> Correlation function

• Objc_msgsend: Sending a message to an object
• Class_copymethodlist: Traversing all methods of a class
• Class_copyivarlist: Traversing all member variables of a class

• NSString *nsstringfromselector (SEL aselector); method name to String

• SEL nsselectorfromstring (nsstring *aselectorname); string Goto method Name

• nsstring *nsstringfromclass (class AClass); class name to String

• Class nsclassfromstring (nsstring *aclassname); string goto class name

• nsstring *nsstringfromprotocol (Protocol *proto); protocol name to String
  

• Protocol *nsprotocolfromstring (nsstring *namestr); string to protocol name
  

• This is the function we must know to learn the runtime!

4. Essential Knowledge
1> Ivar: Member variable
2> method: Member Methods
From the example above we see the member variables that we define, and if you are dynamically creating methods, you can use method,

Runtime mechanism principle and application