十六、KVC

作者: Mjs | 来源:发表于2020-10-27 10:03 被阅读0次

我们了解KVC可以从官文文档来认识，这里简单说下。
键值编码是由NSKeyValueCoding非正式协议启用的一种机制，对象采用这种机制来提供对其属性的间接访问。当对象符合键值编码时，可以通过简洁，统一的消息传递接口通过字符串参数来访问其属性。这种间接访问机制补充了实例变量及其关联的访问器方法提供的直接访问。

KVC简单使用


@interface LGStudent : NSObject
@property (nonatomic, copy)   NSString          *name;
@property (nonatomic, copy)   NSString          *subject;
@property (nonatomic, copy)   NSString          *nick;
@property (nonatomic, assign) int               age;
@property (nonatomic, assign) int               length;
@property (nonatomic, strong) NSMutableArray    *penArr;
@end

typedef struct {
    float x, y, z;
} ThreeFloats;

@interface LGPerson : NSObject{
   @public
   NSString *myName;
}

@property (nonatomic, copy)   NSString          *name;
@property (nonatomic, strong) NSArray           *array;
@property (nonatomic, strong) NSMutableArray    *mArray;
@property (nonatomic, assign) int age;
@property (nonatomic)         ThreeFloats       threeFloats;
@property (nonatomic, strong) LGStudent         *student;

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    int x = arc4random() % 11;
    NSLog(@"%d",x);
  
    LGPerson *person = [[LGPerson alloc] init];
    // 一般setter 方法
    person.name      = @"LG_Cooci"; // setter -- llvm
    person.age       = 18;
    person->myName   = @"cooci";
    NSLog(@"%@ - %d - %@",person.name,person.age,person->myName);
   
    // 1:Key-Value Coding (KVC) : 基本类型 - 看底层原理
    // 非正式协议 - 间接访问
    [person setValue:@"KC" forKey:@"name"];
    
    // 2:KVC - 集合类型
    person.array = @[@"1",@"2",@"3"];
    // 修改数组
    // person.array[0] = @"100";
    // 第一种:搞一个新的数组 - KVC 赋值就OK
    NSArray *array = [person valueForKey:@"array"];
    array = @[@"100",@"2",@"3"];
    [person setValue:array forKey:@"array"];
    NSLog(@"%@",[person valueForKey:@"array"]);
    // 第二种
    NSMutableArray *mArray = [person mutableArrayValueForKey:@"array"];
    mArray[0] = @"200";
    NSLog(@"%@",[person valueForKey:@"array"]);

    // 3:KVC - 集合操作符

    // 4:KVC - 访问非对象属性 - 面试可能问到
    // 结构体
    ThreeFloats floats = {1.,2.,3.};
    NSValue *value     = [NSValue valueWithBytes:&floats objCType:@encode(ThreeFloats)];
    [person setValue:value forKey:@"threeFloats"];
    NSValue *value1    = [person valueForKey:@"threeFloats"];
    NSLog(@"%@",value1);
    
    ThreeFloats th;
    [value1 getValue:&th];
    NSLog(@"%f-%f-%f",th.x,th.y,th.z);
    // 5:KVC - 层层访问 - keyPath
    LGStudent *student = [LGStudent alloc];
    student.subject    = @"大师班";
    person.student     = student;
    
    [person setValue:@"Swift" forKeyPath:@"student.subject"];
    NSLog(@"%@",[person valueForKeyPath:@"student.subject"]);

    [self aggregationOperator];
}


#pragma mark - array取值
- (void)arrayDemo{
    LGStudent *p = [LGStudent new];
    p.penArr = [NSMutableArray arrayWithObjects:@"pen0", @"pen1", @"pen2", @"pen3", nil];
    NSArray *arr = [p valueForKey:@"penArr"]; // 动态成员变量
    NSLog(@"pens = %@", arr);
    //NSLog(@"%@",arr[0]);
    NSLog(@"%d",[arr containsObject:@"pen9"]);
    // 遍历
    NSEnumerator *enumerator = [arr objectEnumerator];
    NSString* str = nil;
    while (str = [enumerator nextObject]) {
        NSLog(@"%@", str);
    }
}

#pragma mark - 字典操作

- (void)dictionaryTest{
    
    NSDictionary* dict = @{
                           @"name":@"Cooci",
                           @"nick":@"KC",
                           @"subject":@"iOS",
                           @"age":@18,
                           @"length":@180
                           };
    LGStudent *p = [[LGStudent alloc] init];
    // 字典转模型
    [p setValuesForKeysWithDictionary:dict];
    NSLog(@"%@",p);
    // 键数组转模型到字典
    NSArray *array = @[@"name",@"age"];
    NSDictionary *dic = [p dictionaryWithValuesForKeys:array];
    NSLog(@"%@",dic);
}

#pragma mark - KVC消息传递
- (void)arrayMessagePass{
    NSArray *array = @[@"Hank",@"Cooci",@"Kody",@"CC"];
    NSArray *lenStr= [array valueForKeyPath:@"length"];
    NSLog(@"%@",lenStr);// 消息从array传递给了string
    NSArray *lowStr= [array valueForKeyPath:@"lowercaseString"];
    NSLog(@"%@",lowStr);
}

#pragma mark - 聚合操作符
// @avg、@count、@max、@min、@sum
- (void)aggregationOperator{
    NSMutableArray *personArray = [NSMutableArray array];
    for (int i = 0; i < 6; i++) {
        LGStudent *p = [LGStudent new];
        NSDictionary* dict = @{
                               @"name":@"Tom",
                               @"age":@(18+i),
                               @"nick":@"Cat",
                               @"length":@(175 + 2*arc4random_uniform(6)),
                               };
        [p setValuesForKeysWithDictionary:dict];
        [personArray addObject:p];
    }
    NSLog(@"%@", [personArray valueForKey:@"length"]);
    
    /// 平均身高
    float avg = [[personArray valueForKeyPath:@"@avg.length"] floatValue];
    NSLog(@"%f", avg);
    
    int count = [[personArray valueForKeyPath:@"@count.length"] intValue];
    NSLog(@"%d", count);
    
    int sum = [[personArray valueForKeyPath:@"@sum.length"] intValue];
    NSLog(@"%d", sum);
    
    int max = [[personArray valueForKeyPath:@"@max.length"] intValue];
    NSLog(@"%d", max);
    
    int min = [[personArray valueForKeyPath:@"@min.length"] intValue];
    NSLog(@"%d", min);
}

// 数组操作符 @distinctUnionOfObjects @unionOfObjects
- (void)arrayOperator{
    NSMutableArray *personArray = [NSMutableArray array];
    for (int i = 0; i < 6; i++) {
        LGStudent *p = [LGStudent new];
        NSDictionary* dict = @{
                               @"name":@"Tom",
                               @"age":@(18+i),
                               @"nick":@"Cat",
                               @"length":@(175 + 2*arc4random_uniform(6)),
                               };
        [p setValuesForKeysWithDictionary:dict];
        [personArray addObject:p];
    }
    NSLog(@"%@", [personArray valueForKey:@"length"]);
    // 返回操作对象指定属性的集合
    NSArray* arr1 = [personArray valueForKeyPath:@"@unionOfObjects.length"];
    NSLog(@"arr1 = %@", arr1);
    // 返回操作对象指定属性的集合 -- 去重
    NSArray* arr2 = [personArray valueForKeyPath:@"@distinctUnionOfObjects.length"];
    NSLog(@"arr2 = %@", arr2);
    
}

// 嵌套集合(array&set)操作 @distinctUnionOfArrays @unionOfArrays @distinctUnionOfSets
- (void)arrayNesting{
    
    NSMutableArray *personArray1 = [NSMutableArray array];
    for (int i = 0; i < 6; i++) {
        LGStudent *student = [LGStudent new];
        NSDictionary* dict = @{
                               @"name":@"Tom",
                               @"age":@(18+i),
                               @"nick":@"Cat",
                               @"length":@(175 + 2*arc4random_uniform(6)),
                               };
        [student setValuesForKeysWithDictionary:dict];
        [personArray1 addObject:student];
    }
    
    NSMutableArray *personArray2 = [NSMutableArray array];
    for (int i = 0; i < 6; i++) {
        LGPerson *person = [LGPerson new];
        NSDictionary* dict = @{
                               @"name":@"Tom",
                               @"age":@(18+i),
                               @"nick":@"Cat",
                               @"length":@(175 + 2*arc4random_uniform(6)),
                               };
        [person setValuesForKeysWithDictionary:dict];
        [personArray2 addObject:person];
    }
    
    // 嵌套数组
    NSArray* nestArr = @[personArray1, personArray2];
    
    NSArray* arr = [nestArr valueForKeyPath:@"@distinctUnionOfArrays.length"];
    NSLog(@"arr = %@", arr);
    
    NSArray* arr1 = [nestArr valueForKeyPath:@"@unionOfArrays.length"];
    NSLog(@"arr1 = %@", arr1);
}

- (void)setNesting{
    
    NSMutableSet *personSet1 = [NSMutableSet set];
    for (int i = 0; i < 6; i++) {
        LGStudent *person = [LGStudent new];
        NSDictionary* dict = @{
                               @"name":@"Tom",
                               @"age":@(18+i),
                               @"nick":@"Cat",
                               @"length":@(175 + 2*arc4random_uniform(6)),
                               };
        [person setValuesForKeysWithDictionary:dict];
        [personSet1 addObject:person];
    }
    NSLog(@"personSet1 = %@", [personSet1 valueForKey:@"length"]);
    
    NSMutableSet *personSet2 = [NSMutableSet set];
    for (int i = 0; i < 6; i++) {
        LGPerson *person = [LGPerson new];
        NSDictionary* dict = @{
                               @"name":@"Tom",
                               @"age":@(18+i),
                               @"nick":@"Cat",
                               @"length":@(175 + 2*arc4random_uniform(6)),
                               };
        [person setValuesForKeysWithDictionary:dict];
        [personSet2 addObject:person];
    }
    NSLog(@"personSet2 = %@", [personSet2 valueForKey:@"length"]);

    // 嵌套set
    NSSet* nestSet = [NSSet setWithObjects:personSet1, personSet2, nil];
    // 交集
    NSArray* arr1 = [nestSet valueForKeyPath:@"@distinctUnionOfSets.length"];
    NSLog(@"arr1 = %@", arr1);
}

Setter

按此顺序查找第一个名为set<Key>:or的访问器_set<Key>。如果找到，请使用输入值（或根据需要解包的值）调用它并完成。
如果没有找到简单的访问，如果类方法accessInstanceVariablesDirectly返回YES，寻找一个实例变量与名称类似_<key>，_is<Key>，<key>，或者is<Key>，按照这个顺序。如果找到，则直接使用输入值（或展开值）设置变量并完成操作。
在找不到访问器或实例变量后，调用setValue:forUndefinedKey:。默认情况下会引发异常，但是的子类NSObject可能提供特定于键的行为。

Getter

搜索实例与像一个名字找到的第一个访问方法get<Key>，<key>，is<Key>，或者_<key>，按照这个顺序。如果找到，则调用它并执行步骤5。否则，继续下一步。
如果未找到简单的访问器方法，请在实例中搜索其名称与模式countOf<Key>和objectIn<Key>AtIndex:（与NSArray该类定义的原始方法<key>AtIndexes:相对应）和（与该[NSArray](https://developer.apple.com/library/archive/documentation/LegacyTechnologies/WebObjects/WebObjects_3.5/Reference/Frameworks/ObjC/Foundation/Classes/NSArrayClassCluster/Description.html#//apple_ref/occ/cl/NSArray)方法相对应）相匹配的方法objectsAtIndexes:。

如果找到其中的第一个以及其他两个中的至少一个，则创建一个响应所有NSArray方法的集合代理对象并将其返回。否则，请继续执行步骤3。

代理对象随后将任何NSArray接收到的一些组合的消息countOf<Key>，objectIn<Key>AtIndex:和<key>AtIndexes:消息给键-值编码创建它兼容的对象。如果原始对象还实现了名称为的可选方法get<Key>:range:，则代理对象也会在适当时使用该方法。实际上，代理对象与与键值编码兼容的对象一起使用，可以使基础属性的行为就好像它是NSArray，即使不是。
如果没有找到简单的访问方法或阵列访问方法组，寻找一个三重的方法命名countOf<Key>，enumeratorOf<Key>和memberOf<Key>:（对应于由所定义的原始的方法[NSSet](https://developer.apple.com/library/archive/documentation/LegacyTechnologies/WebObjects/WebObjects_3.5/Reference/Frameworks/ObjC/Foundation/Classes/NSSetClassCluster/Description.html#//apple_ref/occ/cl/NSSet)类）。

如果找到所有三个方法，请创建一个响应所有NSSet方法的集合代理对象并将其返回。否则，请继续执行步骤4。

随后，此代理对象将NSSet收到的任何消息转换为，和消息的某种组合countOf<Key>，以创建该对象的对象。实际上，代理对象与与键值编码兼容的对象一起使用，可以使基础属性的行为就好像它是，即使不是。 enumeratorOf<Key>``memberOf<Key>:``NSSet
如果发现收集的访问方法没有简单的存取方法或者组，如果接收器的类方法[accessInstanceVariablesDirectly](https://developer.apple.com/library/archive/documentation/LegacyTechnologies/WebObjects/WebObjects_3.5/Reference/Frameworks/ObjC/EOF/EOControl/Classes/NSObjectAdditions/Description.html#//apple_ref/occ/clm/NSObject/accessInstanceVariablesDirectly)返回YES，搜索名为实例变量_<key>，_is<Key>，<key>，或者is<Key>，按照这个顺序。如果找到，请直接获取实例变量的值，然后继续执行步骤5。否则，请继续执行步骤6。
如果检索到的属性值是对象指针，则只需返回结果。

如果该值是所支持的标量类型NSNumber，则将其存储在NSNumber实例中并返回它。

如果结果是NSNumber不支持的标量类型，请转换为NSValue对象并返回该对象。
如果其他所有方法均失败，请调用[valueForUndefinedKey:](https://developer.apple.com/documentation/objectivec/nsobject/1413457-value)。默认情况下会引发异常，但是的子类NSObject可能提供特定于键的行为。

最后我们简单实现下

@implementation NSObject (LGKVC)


-(void)lg_setValue:(nullable id)value forKey:(NSString*)key{
    //1.判断key
    if (key == nil || key.length ==0) {
        return;
    }
    
    //2. setter set<Key>: or _set<Key>
    // key要大写
    NSString *Key = key.capitalizedString;
    //拼接方法
    NSString *setKey = [NSString stringWithFormat:@"set%@:",Key];
    NSString *_setKey = [NSString stringWithFormat:@"_set%@:",Key];
    NSString *setIsKey = [NSString stringWithFormat:@"setIs%@:",Key];
    
    if ([self lg_performSelectorWithMethodName:setKey value:value]) {
        NSLog(@"*********%@**********",setKey);
        return;
    }else if ([self lg_performSelectorWithMethodName:_setKey value:value]) {
        NSLog(@"*********%@**********",_setKey);
        return;
    }else if ([self lg_performSelectorWithMethodName:setIsKey value:value]) {
        NSLog(@"*********%@**********",setIsKey);
        return;
    }
    

    // 3: 判断是否响应 accessInstanceVariablesDirectly 返回YES NO 奔溃
    // 3:判断是否能够直接赋值实例变量
    if (![self.class accessInstanceVariablesDirectly] ) {
        @throw [NSException exceptionWithName:@"LGUnknownKeyException" reason:[NSString stringWithFormat:@"****[%@ valueForUndefinedKey:]: this class is not key value coding-compliant for the key name.****",self] userInfo:nil];
    }
    
    // 4: 间接变量
    // 获取 ivar -> 遍历 containsObjct -
    // 4.1 定义一个收集实例变量的可变数组
    NSMutableArray *mArray = [self getIvarListName];
    
    // _<key> _is<Key> <key> is<Key>
    NSString *_key = [NSString stringWithFormat:@"_%@",key];
    NSString *_isKey = [NSString stringWithFormat:@"_is%@",Key];
    NSString *isKey = [NSString stringWithFormat:@"is%@",Key];
    if ([mArray containsObject:_key]) {
        // 4.2 获取相应的 ivar
       Ivar ivar = class_getInstanceVariable([self class], _key.UTF8String);
        // 4.3 对相应的 ivar 设置值
       object_setIvar(self , ivar, value);
       return;
    }else if ([mArray containsObject:_isKey]) {
       Ivar ivar = class_getInstanceVariable([self class], _isKey.UTF8String);
       object_setIvar(self , ivar, value);
       return;
    }else if ([mArray containsObject:key]) {
       Ivar ivar = class_getInstanceVariable([self class], key.UTF8String);
       object_setIvar(self , ivar, value);
       return;
    }else if ([mArray containsObject:isKey]) {
       Ivar ivar = class_getInstanceVariable([self class], isKey.UTF8String);
       object_setIvar(self , ivar, value);
       return;
    }
    
    // 5:如果找不到相关实例
    @throw [NSException exceptionWithName:@"LGUnknownKeyException" reason:[NSString stringWithFormat:@"****[%@ %@]: this class is not key value coding-compliant for the key name.****",self,NSStringFromSelector(_cmd)] userInfo:nil];
    
}

- (nullable id)lg_valueForKey:(NSString *)key{
    
    // 1:刷选key 判断非空
    if (key == nil  || key.length == 0) {
        return nil;
    }

    // 2:找到相关方法 get<Key> <key> countOf<Key>  objectIn<Key>AtIndex
    // key 要大写
    NSString *Key = key.capitalizedString;
    // 拼接方法
    NSString *getKey = [NSString stringWithFormat:@"get%@",Key];
    NSString *countOfKey = [NSString stringWithFormat:@"countOf%@",Key];
    NSString *objectInKeyAtIndex = [NSString stringWithFormat:@"objectIn%@AtIndex:",Key];
        
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    if ([self respondsToSelector:NSSelectorFromString(getKey)]) {
        return [self performSelector:NSSelectorFromString(getKey)];
    }else if ([self respondsToSelector:NSSelectorFromString(key)]){
        return [self performSelector:NSSelectorFromString(key)];
    }else if ([self respondsToSelector:NSSelectorFromString(countOfKey)]){
        if ([self respondsToSelector:NSSelectorFromString(objectInKeyAtIndex)]) {
            int num = (int)[self performSelector:NSSelectorFromString(countOfKey)];
            NSMutableArray *mArray = [NSMutableArray arrayWithCapacity:1];
            for (int i = 0; i<num-1; i++) {
                num = (int)[self performSelector:NSSelectorFromString(countOfKey)];
            }
            for (int j = 0; j<num; j++) {
                id objc = [self performSelector:NSSelectorFromString(objectInKeyAtIndex) withObject:@(num)];
                [mArray addObject:objc];
            }
            return mArray;
        }
    }
#pragma clang diagnostic pop
    
    // 3:判断是否能够直接赋值实例变量
    if (![self.class accessInstanceVariablesDirectly] ) {
        @throw [NSException exceptionWithName:@"LGUnknownKeyException" reason:[NSString stringWithFormat:@"****[%@ valueForUndefinedKey:]: this class is not key value coding-compliant for the key name.****",self] userInfo:nil];
    }
    
    // 4.找相关实例变量进行赋值
    // 4.1 定义一个收集实例变量的可变数组
    NSMutableArray *mArray = [self getIvarListName];
    // _<key> _is<Key> <key> is<Key>
    // _name -> _isName -> name -> isName
    NSString *_key = [NSString stringWithFormat:@"_%@",key];
    NSString *_isKey = [NSString stringWithFormat:@"_is%@",Key];
    NSString *isKey = [NSString stringWithFormat:@"is%@",Key];
    if ([mArray containsObject:_key]) {
        Ivar ivar = class_getInstanceVariable([self class], _key.UTF8String);
        return object_getIvar(self, ivar);;
    }else if ([mArray containsObject:_isKey]) {
        Ivar ivar = class_getInstanceVariable([self class], _isKey.UTF8String);
        return object_getIvar(self, ivar);;
    }else if ([mArray containsObject:key]) {
        Ivar ivar = class_getInstanceVariable([self class], key.UTF8String);
        return object_getIvar(self, ivar);;
    }else if ([mArray containsObject:isKey]) {
        Ivar ivar = class_getInstanceVariable([self class], isKey.UTF8String);
        return object_getIvar(self, ivar);;
    }

    return @"";
}


#pragma mark - 相关方法
- (BOOL)lg_performSelectorWithMethodName:(NSString *)methodName value:(id)value{
 
    if ([self respondsToSelector:NSSelectorFromString(methodName)]) {
        
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        [self performSelector:NSSelectorFromString(methodName) withObject:value];
#pragma clang diagnostic pop
        return YES;
    }
    return NO;
}
- (id)performSelectorWithMethodName:(NSString *)methodName{
    if ([self respondsToSelector:NSSelectorFromString(methodName)]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        return [self performSelector:NSSelectorFromString(methodName) ];
#pragma clang diagnostic pop
    }
    return nil;
}

- (NSMutableArray *)getIvarListName{
    
    NSMutableArray *mArray = [NSMutableArray arrayWithCapacity:1];
    unsigned int count = 0;
    Ivar *ivars = class_copyIvarList([self class], &count);
    for (int i = 0; i<count; i++) {
        Ivar ivar = ivars[i];
        const char *ivarNameChar = ivar_getName(ivar);
        NSString *ivarName = [NSString stringWithUTF8String:ivarNameChar];
        NSLog(@"ivarName == %@",ivarName);
        [mArray addObject:ivarName];
    }
    free(ivars);
    return mArray;
}
@end

十六、KVC

KVC简单使用

Setter

Getter

最后我们简单实现下

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读