Key-Value Coding(KVC)，存在于NSObject(NSKeyValueCoding)的分类中
普通赋值
[person setValue:@"KC" forKey:@"name"];
赋值并修改数组
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"]);
结构体赋值
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);
keyPath层层访问
LGStudent *student = [LGStudent alloc];
student.subject = @"班级";
person.student = student;
[person setValue:@"Swift" forKeyPath:@"student.subject"];
NSLog(@"%@",[person valueForKeyPath:@"student.subject"]);
具体查看需要查看Apple Developer官方文档进行查看。
查看Key-Value Coding官方文档查看KVC
image
通过官方文档查看Search Pattern for the Basic Setter
官方文档内容为：
20201026142426978.png
通过官方文档可知流程是
image
自定义KVC的代码，如下：
- (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;
}
- (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;
}
- (void)lg_setValue:(nullable id)value forKey:(NSString *)key
{
// KVC 自定义
// 1: 判断什么 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 崩溃
// 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];
}
通过官方文档查看
image
自定义valueForKey方法了解流程
- (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 clang diagnostic ignored "-Warc-performSelector-leaks"
如果selector是在运行时才确定的，perforemSelector时，编译器不知道要执行的selector是什么，那么在ARC下编码代码，编译器会发生如下警告：
warning：performSelector may cause a leak because its selector is unknown [-Warc-performSelector-leak]
原因是：编译器不知道执行的selector是什么，因此也就不了解其方法签名以及返回值，甚至连是否有返回值都不清楚，由于编译器不知道方法名，也就没有办法运用ARC的内存管理原则来判定返回值是不是应该释放，所以ARC采用了一种比较谨慎的方法，就是不添加释放操作，然而这么做有可能导致内存泄漏，因为方法在返回对象时可能已经将其保留了，
如果你确定不会发生内存泄漏的情况下，可以使用该语句来忽略掉这条警告。
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[self performSelector:NSSelectorFromString(methodName) withObject:value];
#pragma clang diagnostic pop
比较全面的自定义KVC
DIS_KVC_KVO源码，根据iOS Foundation框架汇编反写的KVC,KVO实现。
网友评论