Runtime run-time mechanism fully read

We have already talked about a runtime principle, now this article is mainly about what the runtime is and how to use! Hope to help the reader!

First of all, the first question,
1 "Runtime implementation of the mechanism is what, how to use, generally used to do?"
I'm not going to mealy you with this question, just tell everyone,
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")

A second question
What does runtime use for?? Where do you use them? How to use it?
Runtime is the bottom of the OC and can perform some very low-level operations (with OC is not realistic, bad implementation)

• Dynamically create a class during the program's run (for example, the KVO implementation)

• Dynamically add properties \ Methods to a class while the program is running, modify property values \ Methods

• Traverse all member variables (properties) 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++) {

  //Remove member variables corresponding to position IIvar Ivar = ivars[i];//View member variablesConst Char*name = Ivar_getname (Ivar);//ArchiveNSString*key = [NSStringStringwithutf8string:name];IDValue = [ SelfValueforkey:key]; [Encoder Encodeobject:value Forkey:key];

  }

  Free (ivars);
  }

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

  unsigned intCount =0; Ivar *ivars = Class_copyivarlist ([Pyperson class], &count); for(inti =0; i<count; i++) {//Remove member variables corresponding to position IIvar Ivar = ivars[i];//View member variables    Const Char*name = Ivar_getname (Ivar);//Archive    NSString*key = [NSStringStringwithutf8string:name];IDValue = [Decoder decodeobjectforkey:key];//Set to member variable body[ SelfSetvalue: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)
• used to encapsulate the frame (how to change it)  
  This is our runtime mechanism, just use the direction

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
• Class_ .....
  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 run-time mechanism fully read