iOS---14---KVC

作者: 清风烈酒2157 | 来源:发表于2020-12-04 21:15 被阅读0次

iOS---14---KVC

[toc]

什么是KVC？

KVC的全称key - value - coding，俗称 键值编码 ,可以通过key来访问某个属性.

常见方法

- (void)setValue:(id)value forKey:(NSString *)key;
- (void)setValue:(id)value forKeyPath:(NSString *)keyPath;


- (id)valueForKey:(NSString *)key; 
- (id)valueForKeyPath:(NSString *)keyPath;

代码实现:LGTeacher ,LGPerson


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


[person setValue:@"KC" forKey:@"name"];
[person setValue:@19 forKey:@"age"];
[person setValue:@"酷C" forKey:@"myName"];
 NSLog(@"%@ - %@ - %@",[person valueForKey:@"name"],[person valueForKey:@"age"],[person valueForKey:@"myName"]);
 
 person.student = [[LGStudent alloc] init];
//    person.student     = student;
    [person setValue:@"大师班" forKeyPath:@"student.subject"];
    NSLog(@"%@",[person valueForKeyPath:@"student.subject"]);

setValue:(id)value forKeyPath:(NSString *)keyPath 和 setValue:(id)value forKey:(NSString *)key 的区别：

keyPath 相当于根据路径去寻找属性，一层一层往下找，
key 是直接哪去属性的名字设置，如果按路径找会报错

id)valueForKey:(NSString *)key 和 (id)valueForKeyPath:(NSString *)keyPath 的区别：同上

访问非对象属性 ThreeFloats为结构体,转成NSValue

typedef struct {
    float x, y, z;
} ThreeFloats;
访问非对象属性
    ThreeFloats floats = {1., 2., 3.};
    NSValue *value  = [NSValue valueWithBytes:&floats objCType:@encode(ThreeFloats)];
    [person setValue:value forKey:@"threeFloats"];
    NSValue *reslut = [person valueForKey:@"threeFloats"];
    NSLog(@"%@",reslut);

集合类型访问

集合类型 -
    person.array = @[@"1",@"2",@"3"];
    // 由于不是可变数组 - 无法做到
    // person.array[0] = @"100";
    NSArray *array = [person valueForKey:@"array"];
    // 用 array 的值创建一个新的数组
    array = @[@"100",@"2",@"3"];
    [person setValue:array forKey:@"array"];
    NSLog(@"%@",[person valueForKey:@"array"]);

setValue:forKey:的原理

9c69f7f21a2bcebe3e67bb6e2da187b3

当我们设置setValue:forKey:
首先会查找setKey:、_setKey: (按顺序查找),先查找方法
如果有直接调用
如果没有，先查看accessInstanceVariablesDirectly方法

 + (BOOL)accessInstanceVariablesDirectly{
      return YES;   ///> 可以直接访问成员变量
      //    return NO;  ///>  不可以直接访问成员变量,  
      ///> 直接访问会报NSUnkonwKeyException错误  
    }

如果可以访问会按照_key、_isKey、key、iskey的顺序查找成员变量
找到直接复制
未找到报错NSUnkonwKeyException错误

举例,按照_key、_isKey、key、iskey复制顺序

@interface LGPerson : NSObject{
    @public
     NSString *_name;
     NSString *_isName;
     NSString *name;
     NSString *isName;
}

打印

NSLog(@"%@-%@-%@-%@",person->_name,person->_isName,person->name,person->isName);
    
    NSLog(@"%@-%@-%@",person->_isName,person->name,person->isName);
    NSLog(@"%@-%@",person->name,person->isName);
    NSLog(@"%@",person->isName);

依次注释每个成员变量,打印结果也是不一样的

valueForKey的原理

d0aa09c6353d921b4d83ef9c98bbaf9e

kvc取值按照 getKey、key、iskey、_key 顺序查找方法
存在直接调用
没找到同样，先查看accessInstanceVariablesDirectly方法

+ (BOOL)accessInstanceVariablesDirectly{
      return YES;   ///> 可以直接访问成员变量
  //    return NO;  ///>  不可以直接访问成员变量,  
  ///> 直接访问会报NSUnkonwKeyException错误  
  }

如果可以访问会按照 _key、_isKey、key、iskey的顺序查找成员变量
找到直接复制
未找到报错NSUnkonwKeyException错误

自定义kvc

新建一个 NSObject的分类,根据官网的查找和取值顺序做了一些处理.
1.首先要判空.
2.相同方法等考虑字符串拼接方式

思路

先查找方法
查找成员变量
都没有找到报错

#import "NSObject+LGKVC.h"
#import <objc/runtime.h>
@implementation NSObject (LGKVC)

# pmara mark ------ lg_setValue
- (void)lg_setValue:(nullable id)value forKey:(NSString *)key{
    
    // 1:非空判断一下
    if (key == nil  || key.length == 0) return;
    
    // 2:找到相关方法 set<Key> _set<Key> setIs<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>
    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];
}

# pmara mark ------ lg_valueForKey
- (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

KVC小技巧

写一个LGPerson

typedef struct {
    float x, y, z;
} ThreeFloats;
@interface LGPerson : NSObject{
    @public
    NSString *name;
    NSString *_name;
    NSString *_isName;
    NSString *isName;
    
}
@property (nonatomic, copy) NSString *subject;
@property (nonatomic, assign) int  age;
@property (nonatomic, assign) BOOL sex;
@property (nonatomic) ThreeFloats  threeFloats;

KVC 自动转换类型

int类型 bool类型传进去值为string,有时候会转成相应的 __NSCFNumber类型

[person setValue:@18 forKey:@"age"];
    // 上面那个表达 大家应该都会! 但是下面这样操作可以?
    [person setValue:@"20" forKey:@"age"]; // int - string
    NSLog(@"%@-%@",[person valueForKey:@"age"],[[person valueForKey:@"age"] class]);//__NSCFNumber
    
    [person setValue:@"20" forKey:@"sex"];
    NSLog(@"%@-%@",[person valueForKey:@"sex"],[[person valueForKey:@"sex"] class]);//__NSCFNumber

结构体会转成NSConcreteValue

ThreeFloats floats = {1., 2., 3.};
    NSValue *value  = [NSValue valueWithBytes:&floats objCType:@encode(ThreeFloats)];
    [person setValue:value forKey:@"threeFloats"];
    NSLog(@"%@-%@",[person valueForKey:@"threeFloats"],[[person valueForKey:@"threeFloats"] class]);//NSConcreteValue

设置空值

官网解释:如果调用-set value:forKey:将无法设置键空值，因为对应访问器方法的参数类型是NSNumber标量类型或NSValue结构类型，但该值为nil，请使用其他机制设置键空值。此方法的默认实现引发NSInvalidArgumentException。您可以重写它，将nil值映射到应用程序上下文中有意义的内容。

[person setValue:nil forKey:@"age"]; // subject不会走 - 官方注释里面说只对 NSNumber - NSValue
    [person setValue:nil forKey:@"subject"];
    
   // 重写setNilValueForKey
- (void)setNilValueForKey:(NSString *)key{
    NSLog(@"你傻不傻: 设置 %@ 是空值",key);
}

找不到key

[person setValue:nil forKey:@"KC"];

处理:重写forUndefinedKey

- (void)setValue:(id)value forUndefinedKey:(NSString *)key{
    NSLog(@"你瞎啊: %@ 没有这个key",key);
}

取值时 - 找不到 key

NSLog(@"%@",[person valueForKey:@"KC"]);

处理:重写valueForUndefinedKey

- (id)valueForUndefinedKey:(NSString *)key{
    NSLog(@"你瞎啊: %@ 没有这个key - 给你一个其他的吧,别奔溃了!",key);
    return @"Master 牛逼";
}

iOS---14---KVC
[toc] 什么是KVC？ KVC的全称key - value - coding，俗称键值编码 ,可以通过key...

iOS---14---KVC

什么是KVC？

常见方法

setValue:forKey:的原理

valueForKey的原理

自定义kvc

KVC小技巧

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iOS---14---KVC

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