The Runtime based
1.Runtime related header files
To learn the Runtime source code first-hand, look at the following three header files.
#import <objc/runtime.h>
#import <objc/message.h>
#import <objc/objc.h>
Copy the codeRuntime several important structures
As you can see from the structure, there is only one ISA pointer inside the instance, pointing to its own class.
/ / instance
struct objc_object {
Class _Nonnull isa OBJC_ISA_AVAILABILITY;
};
Copy the codeThe following is a description of the structure of the class.
/ / class
struct objc_class {
// The isa pointer to the class points to its own metaclass
Class _Nonnull isa OBJC_ISA_AVAILABILITY;
#if! __OBJC2__// super_class refers to the superclass
Class _Nullable super_class OBJC2_UNAVAILABLE;
const char * _Nonnull name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
// Member variables
struct objc_ivar_list * _Nullable ivars OBJC2_UNAVAILABLE;
/ / method
struct objc_method_list * _Nullable * _Nullable** methodLists OBJC2_UNAVAILABLE;
// Method cache
struct objc_cache * _Nonnull cache OBJC2_UNAVAILABLE;
// The protocol to follow
struct objc_protocol_list * _Nullable protocols OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
Copy the codeClass defines class-related properties in the structure of the class. The following two structures are highlighted: instance variable array and method array. Objc_ivar_list Array of member variables
// Member variables
struct objc_ivar {
/ / variable names
char * _Nullable ivar_name OBJC2_UNAVAILABLE;
// Variable type
char * _Nullable ivar_type OBJC2_UNAVAILABLE;
int ivar_offset OBJC2_UNAVAILABLE;
#ifdef __LP64__
int space OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
// Can be thought of as an array, the array element is objc_ivar
struct objc_ivar_list {
int ivar_count OBJC2_UNAVAILABLE;
#ifdef __LP64__
int space OBJC2_UNAVAILABLE;
#endif
/* variable length structure */
struct objc_ivar ivar_list[1] OBJC2_UNAVAILABLE;
}
Copy the codeObjc_method_list Array of methods
struct objc_method {
/ / the method name
SEL _Nonnull method_name OBJC2_UNAVAILABLE;
char * _Nullable method_types OBJC2_UNAVAILABLE;
// The function that the method actually executes
IMP _Nonnull method_imp OBJC2_UNAVAILABLE;
} OBJC2_UNAVAILABLE;
// Can be thought of as an array of methods, each element objc_method
struct objc_method_list {
struct objc_method_list * _Nullable obsolete OBJC2_UNAVAILABLE;
int method_count OBJC2_UNAVAILABLE;
#ifdef __LP64__
int space OBJC2_UNAVAILABLE;
#endif
/* variable length structure */
struct objc_method method_list[1] OBJC2_UNAVAILABLE;
}
Copy the code3. Correlation function
3.1 Obtaining the Class Name
Get the class name dynamically from a class, but class_getName returns a C string that needs to be converted to OC via NSString.
+ (NSString *)fetchClassName:(Class)class {
const char *className = class_getName(class);
return [NSString stringWithUTF8String:className];
}
Copy the code3.2 Obtaining member Variables
The following fetchIvarList gets the list of instance variables via class_copyIvarList, then ivar_getName gets the variable name, ivar_getTypeEncoding gets the variable type, and saves the variable name and type into an array via a dictionary.
+ (NSArray *)fetchIvarList:(Class)class {
unsigned int count = 0;
Ivar *ivarList = class_copyIvarList(class, &count);
NSMutableArray *mutableList = [NSMutableArray new];
for (int i = 0; i < count; i++) {
NSMutableDictionary *dictM = [NSMutableDictionary new];
const char *ivarName = ivar_getName(ivarList[i]);
const char *ivarType = ivar_getTypeEncoding(ivarList[i]);
dictM[@"type"] = [NSString stringWithUTF8String:ivarType];
dictM[@"ivarName"] = [NSString stringWithUTF8String:ivarName];
[mutableList addObject:dictM];
}
// Remember to release it, otherwise memory leaks
free(ivarList);
return [NSArray arrayWithArray:mutableList];
}
Copy the code3.3 Obtaining Attributes
Class_copyPropertyList gets an array of member variables. Property_getName gets the name of the variable. The method calls are very similar.
+ (NSArray *)fetchPropertyList:(Class)class {
unsigned int count = 0;
objc_property_t *propertyList = class_copyPropertyList(class, &count);
NSMutableArray *mutableList = [NSMutableArray new];
for (int i = 0; i < count; i++) {
const char *propertyName = property_getName(propertyList[i]);
[mutableList addObject:[NSString stringWithUTF8String:propertyName]];
}
// Also need to release
free(propertyList);
return [NSArray arrayWithArray:mutableList];
}
Copy the code3.4 Getting instance methods of a class
The enclosed fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList fetchMethodList And then I get the method name by NSStringFromSelector.
+ (NSArray *)fetchMethodList:(Class)class {
unsigned int count = 0;
Method *methodList = class_copyMethodList(class, &count);
NSMutableArray *mutalbelist = [NSMutableArray new];
for (int i = 0; i < count; i++) {
SEL methodSel = method_getName(methodList[i]);
NSString *methodName = NSStringFromSelector(methodSel);
[mutalbelist addObject:methodName];
}
free(methodList);
return [NSArray arrayWithArray:mutalbelist];
}
Copy the code3.5 Dynamic Adding Method
Dynamic method addition may be used less in the actual development, but in the message forwarding and crash processing can dynamically add methods to the object, to prevent program crash. The following is a method that adds a run to the current instance self via class_addMethod. The run method is just an SEL, and the actual function is myRun; The first parameter is the class to which the method needs to be added, the second parameter is the name of the method to be added, the third parameter is the function that the method actually executes, and the fourth parameter is the @encode instruction of the method parameter. Please refer to this section for the introduction of @encode instruction. V :void @ object ->self -> SEL->_cmd
class_addMethod(object_getClass(self), @selector(run:), (IMP)myRun, "v@:");
[self performSelector:@selector(run:) withObject:@"Ha ha"];
Copy the code// IMP must take at least two arguments self and _cmd, other arguments can be added after the comma separated
void myRun(id self, SEL _cmd, id obj) {
NSLog(@"sel:%@, obj:%@", NSStringFromSelector(_cmd), obj);
}
// Print the following result
selRun: obj: ha haCopy the code3.6 Method Exchange
Method interchange is widely used in the whole Apple system and is often used in our actual development. The detailed usage will be introduced in the Runtime application scenario. Class_getInstanceMethod can find the corresponding Method in the class by using SEL selector.class_getInstancemethod And then call method_exchangeImplementations so we can implement the exchange of the two methods.
+ (void)methodSwap:(Class)class firstSel: (SEL)firstSel secondSel: (SEL)secondSel {
Method firstMethod = class_getInstanceMethod(class.firstSel);
Method secondMethod = class_getInstanceMethod(class.secondSel);
method_exchangeImplementations(firstMethod, secondMethod);
}
Copy the codeWe can just test it in the ViewController and see if it’s really interchangeable, right? Swap the two methods in the load method. From the printed information, you can see that the order in which the two methods are called has actually been reversed, indicating that the methods have indeed been switched.
+ (void)load {
[super load];
[self methodSwap:self firstSel: @selector(sayHello1) secondSel: @selector(sayHello2)];
}
- (void)viewDidLoad {
[self sayHello1];
[self sayHello2];
}
- (void)sayHello1 {
NSLog(@"sayHello1");
}
- (void)sayHello2 {
NSLog(@"sayHello2");
}
// Print the following result
2021-10-20 18:09:18.280476+0800 abffff[5660:200359] sayHello2
2021-10-20 18:09:18.280632+0800 abffff[5660:200359] sayHello1
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