爱站程序员基地KVC（Key-value coding）
键值编码
基本使用
- 能够对对象的私有成员进行取值赋值
- 对数值和结构体型的属性进行的打包解包处理
实例：
WTPerson.h
#import@interface WTPerson : NSObject{// @public //@protect默认 NSString * _name;}/** name **///@property(nonatomic,strong)NSString * name;@end复制代码
ViewController.m
#import \"ViewController.h\"#import \"WTPerson.h\"@interface ViewController ()@property (weak, nonatomic) IBOutlet UITextField *text;@end@implementation ViewController- (void)viewDidLoad { [super viewDidLoad]; WTPerson * p = [WTPerson new]; //访问成员变量 //p.name = @\"wt\"; //NSLog(@\"%@\",p.name); //访问私有变量（必须要要设置为public才可访问） //p->_name = @\"wt\"; //NSLog(@\"%@\",p->_name); //KVC(即使不用public修饰，也可以访问私有变量) [p setValue:@\"wt\" forKey:@\"name\"]; NSLog(@\"%@\",[p valueForKey:@\"name\"]); [self.text setValue:[UIColor redColor] forKeyPath:@\"_placeholderLabel.textColor\"];}复制代码
KVC赋值取值过程分析和自定义及异常处理
赋值过程
- 1、先找相关方法set
- 2、若是没有相关方法+(BOOL)accessInstanceVariablesDirectly判断是否可以直接访问成员变量
- 3、如果判断NO，直接执行KVC的setValue:forUndefinedKey:(系统抛出一个异常，未定义key)
- 4、如果是YES，继续找相关变量_
- 5、方法或成员都不存在，setValue:forUndefinedKey:方法默认是抛出异常
实例验证
WTPerson.h
#import@interface WTPerson : NSObject{ @public //@protect默认 NSString * _name; NSString * _isName; NSString * name; NSString * isName;}@end复制代码
WTPerson.m
#import \"WTPerson.h\"@implementation WTPerson-(void)setName:(NSString *)name{ NSLog(@\"%s\",__func__);}-(void)_setName:(NSString *)name{ NSLog(@\"%s\",__func__);}-(void)setIsName:(NSString *)name{ NSLog(@\"%s\",__func__);}@end复制代码
ViewController.m
#import \"ViewController.h\"#import \"WTPerson.h\"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad { [super viewDidLoad]; WTPerson * p = [WTPerson new]; //验证KVC赋值过程 [p setValue:@\"wt\" forKey:@\"name\"]; NSLog(@\"name = %@\",p->name); NSLog(@\"_name = %@\",p->_name); NSLog(@\"isname = %@\",p->isName); NSLog(@\"_isname = %@\",p->_isName);}@end复制代码
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运行程序，我们把WTPerson.m中的-(void)setName:(NSString *)name、-(void)_setName:(NSString *)name、-(void)setIsName:(NSString *)name三个方法依次注释，我们发现三个方法都会被依次执行。
-
然后我们把WTPerson.h中的NSString * _name;、NSString * _isName;、NSString * name;、NSString * isName;依次注释，我们会发现4个属性依次被赋值。
在WTPerson.m中我们让accessInstanceVariablesDirectly返回NO，则程序直接崩溃。
+ (BOOL)accessInstanceVariablesDirectly{ return NO;}复制代码
取值过程
- 1、先找相关方法get
- 2、若没有相关方法，+(BOOL)accessInstanceVariabkesDirectly判断是否可以直接访问成员变量
- 3、如果是NO，直接执行KVC的valueForUndefinedKey:(系统抛出一个异常，未定义key)
- 4、如果是YES，继续找相关变量_
- 5、方法或成员都不存在，valueForUndefineKey:方法，默认是抛出异常
实例验证
WTPerson.m
#import \"WTPerson.h\"@implementation WTPerson//- (NSString*) getName{// NSLog(@\"%s\",__func__);// return @\"getName\";//}- (NSString*) name { return @\"name\";}//+ (BOOL)accessInstanceVariablesDirectly{// return NO;//}@end复制代码
ViewController.m
#import \"ViewController.h\"#import \"WTPerson.h\"@interface ViewController ()@property (weak, nonatomic) IBOutlet UITextField *text;@end@implementation ViewController- (void)viewDidLoad { [super viewDidLoad]; WTPerson * p = [WTPerson new]; //验证KVC取值过程 NSLog(@\"name = %@\",[p valueForKey:@\"name\"]);}@end复制代码
取值方式与赋值方式大致相同。
KVC自定义
自定义KVC代码实现
创建分类NSObject+KVC
NSObject+KVC.h
#import@interface NSObject (KVC)- (void)wt_setValue:(nullable id)value forKey:(NSString *)key;- (id)wt_valueForKey:(NSString *)key;@end复制代码
NSObject+KVC.m
#import \"NSObject+KVC.h\"#import@implementation NSObject (KVC)- (id)wt_valueForKey:(NSString *)key{ //判断是否合法 if (key == nil && key.length ==0) { return nil; } //Key NSString * Key = key.capitalizedString; //先找相关方法 get,key NSString * getKey = [NSString stringWithFormat:@\"get%@:\",Key]; if ([self respondsToSelector:NSSelectorFromString(getKey)]) { return [self performSelector:NSSelectorFromString(getKey)]; } if ([self respondsToSelector:NSSelectorFromString(key)]) { return [self performSelector:NSSelectorFromString(key)]; } if (![self.class accessInstanceVariablesDirectly]) { NSException * exception = [NSException exceptionWithName:@\"NSUnknownKeyException\" reason:@\"setValue:forUndefineKey\" userInfo:nil]; @throw exception; } //再找相关变量 //获取所有的成员变量 unsigned int count = 0; Ivar * ivars = class_copyIvarList([self class], &count); NSMutableArray * arr = [[NSMutableArray alloc]init]; for (int i = 0; i<count; i++) { Ivar var = ivars[i]; const char * varName = ivar_getName(var); NSString *name = [NSString stringWithUTF8String:varName]; [arr addObject:name]; } //__isisfor (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"_%@\",key]]) { return object_getIvar(self, ivars[i]); } } for (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"_is%@\",Key]]) { return object_getIvar(self, ivars[i]); } } for (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"%@\",key]]) { return object_getIvar(self, ivars[i]); } } for (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"is%@\",Key]]) { return object_getIvar(self, ivars[i]); } } free(ivars); return nil;}- (void)wt_setValue:(nullable id)value forKey:(NSString *)key{ //判断是否合法 if (key == nil && key.length ==0) { return; } //Key NSString * Key = key.capitalizedString; //先找相关方法 set; _set; setIs; NSString * setKey = [NSString stringWithFormat:@\"set%@:\",Key]; if ([self respondsToSelector:NSSelectorFromString(setKey)]) { [self performSelector:NSSelectorFromString(setKey) withObject:value]; return; } NSString * _setKey = [NSString stringWithFormat:@\"_set%@:\",Key]; if ([self respondsToSelector:NSSelectorFromString(_setKey)]) { [self performSelector:NSSelectorFromString(_setKey) withObject:value]; return; } NSString * setIsKey = [NSString stringWithFormat:@\"setIs%@:\",Key]; if ([self respondsToSelector:NSSelectorFromString(setIsKey)]) { [self performSelector:NSSelectorFromString(setIsKey) withObject:value]; return; } if (![self.class accessInstanceVariablesDirectly]) { NSException * exception = [NSException exceptionWithName:@\"NSUnknownKeyException\" reason:@\"setValue:forUndefineKey\" userInfo:nil]; @throw exception; } //再找相关变量 //获取所有的成员变量 unsigned int count = 0; Ivar * ivars = class_copyIvarList([self class], &count); NSMutableArray * arr = [[NSMutableArray alloc]init]; for (int i = 0; i<count; i++) { Ivar var = ivars[i]; const char * varName = ivar_getName(var); NSString *name = [NSString stringWithUTF8String:varName]; [arr addObject:name]; } //__isisfor (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"_%@\",key]]) { object_setIvar(self, ivars[i], value); free(ivars); return; } } for (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"_is%@\",Key]]) { object_setIvar(self, ivars[i], value); free(ivars); return; } } for (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"%@\",key]]) { object_setIvar(self, ivars[i], value); free(ivars); return; } } for (int i = 0; i < count; i++) { NSString *keyName = arr[i]; if ([keyName isEqualToString:[NSString stringWithFormat:@\"is%@\",Key]]) { object_setIvar(self, ivars[i], value); free(ivars); return; } } [self setValue:value forUndefinedKey:Key]; free(ivars);}@end复制代码
验证
ViewController.m
#import \"ViewController.h\"#import \"WTPerson.h\"#import \"NSObject+KVC.h\"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad { [super viewDidLoad]; WTPerson * p =[WTPerson new]; [p wt_setValue:@\"wt\" forKey:@\"name\"]; NSLog(@\"name-KVC = %@\",[p wt_valueForKey:@\"name\"]); NSLog(@\"_name = %@\",p->_name); NSLog(@\"_isName = %@\",p->_isName); NSLog(@\"name = %@\",p->name); NSLog(@\"isName = %@\",p->isName);}@end复制代码
在项目中
commond+shift+o 搜索setValue:forKey发现在Foundation框架下的NSKeyValueCoding文件下
我们查看这个文件中的方法，发现这个文件中是一些分类的集合
KVC异常处理及正确性验证
KVC异常处理
- 1、赋值为空 setNilValueForKey
- 2、Key值不存在 setValue:forUndefinedKey
正确性验证
validateValue
该方法的工作原理：
- 1、先找一下你的类中是否实现了方法 -(BOOL)validate
- 2、如果实现了就会根据实现方法里面的自定义逻辑返回NO或者YES；如果没有实现这个方法，则系统默认返回YES
示例代码
WTPerson…h
#import@interface WTPerson : NSObject/** name **/@property(nonatomic,strong)NSString * name;/** age **/@property(nonatomic,assign)int age;@end复制代码
WTPerson.m
#import \"WTPerson.h\"@implementation WTPerson//对非对象类型，值不能为空- (void) setNilValueForKey:(NSString *)key{ NSLog(@\"%@ 值不能为空\",key);}//赋值的key不存在- (void) setValue:(id)value forUndefinedKey:(NSString *)key{ NSLog(@\"key = %@值不存在\",key);}//取值的key不存在- (id) valueForUndefinedKey:(NSString *)key{ NSLog(@\"key = %@值不存在\",key); return nil;}//正确性验证- (BOOL) validateAge:(inout id _Nullable __autoreleasing *)ioValue error:(out NSError * _Nullable __autoreleasing *)outError{ NSNumber* value = (NSNumber*)*ioValue; NSLog(@\"%@\",value); if ([value integerValue] >= 0 && [value integerValue] <= 200) { return YES; } return NO;}@end复制代码
ViewController.m
#import \"ViewController.h\"#import \"WTPerson.h\"#import \"WTContainer.h\"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad { [super viewDidLoad]; WTPerson * p = [WTPerson new]; //异常处理 [p setValue:@18 forKey:@\"name\"]; [p setValue:nil forKey:@\"name\"]; NSLog(@\"name = %@\",p.name); [p setValue:nil forKey:@\"age\"]; NSLog(@\"age = %d\",p.age); [p setValue:@\"hello\" forKey:@\"name1\"]; NSLog(@\"name = %@\",[p valueForKey:@\"name1\"]); //万能容器 WTContainer * container = [WTContainer new]; [container setValue:@\"wt\" forKey:@\"name\"]; [container setValue:@18 forKey:@\"age\"]; NSLog(@\"name = %@,age = %@\",[container valueForKey:@\"name\"],[container valueForKey:@\"age\"]); //正确性验证 NSNumber * value = @200; NSNumber * value1 = @199; if ([p validateValue:&value1 forKey:@\"age\" error:NULL]) { [p setValue:value1 forKey:@\"age\"]; } NSLog(@\"%@\",[p valueForKey:@\"age\"]);}@end
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