Good articles to my personal technology blog: https://cainluo.github.io/15034954202343.html

We have come to the third part of our tutorial on loading technology. If you haven’t seen the previous part, you can go to playing iOS development: Loading Technology in iOS Development – RunTime(2).

What is it this time? Let’s take a look

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Automatic archive

What do we do when we file? Take a look at the code:

- (id)initWithCoder:(NSCoder *)decoder {
    
    self = [super init];
    
    if (self = [super init]) {
    
        NSObject *obj = [decoder decodeObjectForKey:@"keyName"];
    }
    
    return self;
}

- (void)encodeWithCoder:(NSCoder *)coder {
    
    NSObject *obj = [[NSObject alloc] init];

    [coder encodeObject:obj
                 forKey:@"keyName"];
}
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It seems like there’s no problem, but what if we have a hundred files, then we have to write them one by one, a hundred each, and they’re weak.

There must be a better way to do this, and the Runtime can be archived after several steps:

  • throughclass_copuIvarListMethod to get the currentModelAll member variables of.
  • throughivar_getNameMethod to get the name of a member variable.
  • throughKVCTo read theModelProperty value, and finally giveModelAssigns the property of the.

For example, 🌰 creates a new Model class named CoderModel with the following code:

#import "CoderModel.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation CoderModel

- (void)encodeWithCoder:(NSCoder *)coder{
    
    unsigned int outCount = 0;
    
    Ivar *vars = class_copyIvarList([self class], &outCount);
    
    for (int i = 0; i < outCount; i ++) {
        
        Ivar var = vars[i];
        
        const char *name = ivar_getName(var);
        
        NSString *key = [NSString stringWithUTF8String:name];
        
        id value = [self valueForKey:key];
        
        [coder encodeObject:value
                     forKey:key];
    }
    
    free(vars);
}

- (nullable instancetype)initWithCoder:(NSCoder *)decoder{
    
    if (self = [super init]) {
        
        unsigned int outCount = 0;
        
        Ivar *vars = class_copyIvarList([self class], &outCount);
        
        for (int i = 0; i < outCount; i ++) {
            
            Ivar var = vars[i];
            
            const char *name = ivar_getName(var);
            
            NSString *key = [NSString stringWithUTF8String:name];
            
            id value = [decoder decodeObjectForKey:key];
            
            [self setValue:value forKey:key];
        }
        
        free(vars);
    }
    
    return self;
}

@end
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  • Along withKVCAs you know,KVCIf you can findkeyThe properties of thesetterMethod is calledsetterMethods.
  • If you don’t find itsetter, will look for the member variableskeyOr member variables_key
  • So we don’t have to do anything else with prefixes here_Prefix the name of the member variable

Here we also need to write a Category to transform the model, find yourself in the project, and finally implement:

- (void)coderModel {
    
    CoderModel *coderModel = [CoderModel objectWithKeyValues:self.dictionary];
    
    NSLog(@"%@, %ld, %ld", coderModel.name, coderModel.age, coderModel.phoneNumber);
    
    NSDictionary *dictionary = [coderModel keyValuesWithObject];
    
    NSLog(@"dictionary is %@", dictionary);
}
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2017-08-23 22:27:51.349 1.RunTime[36904:3052474] 1.RunTime[36904:3052474] Dictionary is {age = 18; name = "\U5c0f\U660e"; phoneNumber = 13800138000; }Copy the code

Dictionaries interact with models

Now that I’m done with archiving, I’m going to transfer the dictionary and model to each other.

We used to assign values to the model as:

- (instancetype)initWithDictionary:(NSDictionary *)dictionary {

    if (self = [super init]) {
    
        self.age  = dictionary[@"age"];
        self.name = dictionary[@"name"];
    }
    
    return self;
}
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It seems that there is no problem, but in fact it is the same problem as archiving. After using MJMJExtension and YYModel, I found that there are other ways to parse the model.

Let’s look at the process:

  • When the dictionary turns to the model
    • According to the dictionarykeygeneratesettermethods
    • useobjc_msgSendcallsetterMethods forModelIs assigned to or used byKVC
+ (id)objectWithKeyValues:(NSDictionary *)dictionary {
    
    id objc = [[self alloc] init];
    
    for (NSString *key in dictionary.allKeys) {
        
        id value = dictionary[key];
        
        // Determine whether the current attribute belongs to Model
        objc_property_t property = class_getProperty(self, key.UTF8String);
        
        unsigned int outCount = 0;
        
        objc_property_attribute_t *attributeList = property_copyAttributeList(property, &outCount);
        
        objc_property_attribute_t attribute = attributeList[0];
        
        NSString *typeString = [NSString stringWithUTF8String:attribute.value];
        
        if ([typeString isEqualToString:@"@\"CoderModel\""]) {
            
            value = [self objectWithKeyValues:value];
        }
        
        // Generate setter methods and call them with objc_msgSend
        NSString *methodName = [NSString stringWithFormat:@"set%@%@:", [key substringToIndex:1].uppercaseString, [key substringFromIndex:1]];
        
        SEL setter = sel_registerName(methodName.UTF8String);
        
        if ([objc respondsToSelector:setter]) {((void (*) (id,SEL,id)) objc_msgSend) (objc,setter,value);
        }
        
        free(attributeList);
    }
    
    return objc;
}
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  • When the model turns to the dictionary
    • callclass_copyPropertyListMethod to get the currentModelAll attributes of
    • Call property_getName to get the property name
    • Generated from the property namegettermethods
    • useobjc_msgSendcallgetterMethod to get the value of an attribute or use theKVC
- (NSDictionary *)keyValuesWithObject {
    
    unsigned int outCount = 0;
    
    objc_property_t *propertyList = class_copyPropertyList([self class], &outCount);
    
    NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
    
    for (int i = 0; i < outCount; i ++) {
        
        objc_property_t property = propertyList[i];
        
        // Generate getter methods and call them with objc_msgSend
        const char *propertyName = property_getName(property);
        
        SEL getter = sel_registerName(propertyName);
        
        if ([self respondsToSelector:getter]) {
            
            id value = ((id (*) (id,SEL)) objc_msgSend) (self.getter);
            
            // Determine whether the current attribute belongs to Model
            if ([value isKindOfClass:[self class]] && value) {
                
                value = [value keyValuesWithObject];
            }
            
            if (value) {
                
                NSString *key = [NSString stringWithUTF8String:propertyName];
                
                [mutableDictionary setObject:value
                                      forKey:key];
            }
        }
    }
    
    free(propertyList);
    
    return mutableDictionary;
}
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Dynamic method parsing

That’s basically the end of the story, and the last is to add to what I didn’t say in front.

Usually we call a method that doesn’t exist in the object and it crashes with an error message:

unrecognized selector sent to instance 0x0bcde09abc0
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But before the crash, Runtime gives us a chance to do dynamic parsing, which goes something like this:

  • detectionselectorDo you need to ignore, like inmacOSWhat will ARC not care aboutretain.releaseThese are the methods.
  • detectiontargetWhether fornil.Objective-CIs allowed to onenilThe object can execute any method without collapsing, so it is ignored, but inSwiftIt’s going to be a problem.
  • If you pass both of these, you’re going to look for this classIMPFirst, from thecacheInside to find, found to jump to the corresponding function to execute.
    • ifcacheCan not find a method to be published
  • If you can’t find it in the distribution table, you’ll look in the distribution table of the superclass and keep finding itNSObject.
  • If not, the message will start forwarding

General process of forwarding:

The picture was stolen from some blog post on the Internet. I don’t want to draw it.

  • Into theresolveInstanceMethod:Method, specify whether the method is dynamically added.
    • If the return isNO, will go to the next step
    • If the returnYES, will passclass_addMethodThe function dynamically adds methods, the message is processed, and the process is complete.
  • resolveInstanceMethod:Method returnsNO, will enterforwardingTargetForSelectorMethod, this isRuntimeGive us a second chance to specify which object responds to thisselector.
    • If the returnnil, will go to the next step, return an object, willCalls a method on that object.
  • forwardingTargetForSelector:Return isnilIf so, we need to passmethodSignatureForSelector:To specify the method signature.
    • ifmethodSignatureForSelector:returnnilReturn the method signature and proceed to the next step.
  • whenmethodSignatureForSelector:Method is called when the signature is returnedforwardInvocation:Method, we can go throughanInvocationObject to do processing, for exampleModify the implementation method.Modifying the response objectAnd so on.
  • If at the end, the message is still not being responded to or processed, it will crash.

Let’s look at the code:

#import "BicycleModel.h"
#import "SportsCarModel.h"

#import <objc/runtime.h>

@implementation BicycleModel

- (void)ridingSpeed {
    
    NSLog(@"Slow Ride");
}

+ (BOOL)resolveInstanceMethod:(SEL)sel {
    
#if 0
    return NO;
#else
    class_addMethod(self, sel, class_getMethodImplementation(self, sel_registerName("ridingSpeed")), "v@:");
    
    return [super resolveInstanceMethod:sel];
#endif
}

- (id)forwardingTargetForSelector:(SEL)aSelector{
    
#if 0
    return nil;
#else
    return [[SportsCarModel alloc] init];
#endif
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    
    return [NSMethodSignature signatureWithObjCTypes:"v@:"];
}

- (void)forwardInvocation:(NSInvocation *)anInvocation {
    
    return [anInvocation invokeWithTarget:[[SportsCarModel alloc] init]];
}
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#import "SportsCarModel.h"

@implementation SportsCarModel

- (void)rapidAcceleration {
    
    NSLog(@"High speed");
}

@end
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Execution method:

- (void)dynamicAnalysis {
    
    BicycleModel *bicycle = [[BicycleModel alloc] init];
    
    ((void (*) (id, SEL)) objc_msgSend) (bicycle, sel_registerName("rapidAcceleration"));
}
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Printed results:

2017-08-24 00:09:15.238 1.RunTime[37657:3122648] Slow Ride
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The project address

The address of the project: https://github.com/CainRun/iOS-Project-Example/tree/master/RunTime/Three

The last