《iOS底层原理文章汇总》
1.KVC的一般使用
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"]);
2.访问非对象属性
// 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"]);
3.KVC设值
image.png
设值的过程会先底层查找setName-->_setName-->setIsName,按照此顺序依次进行查找
image.png
开启或关闭实例变量赋值:会按顺序赋值到_name、_isName、name、isName中
image.png
按名字，若其中一位没有了，按照规定，依次找下一个符合的实例变量
image.png
image.png
若都没有呢，程序执行setValue:forUndefinedKey:会崩溃[
4.KVC取值
image.png
valueForKey 流程分析
- get, , is, or _ 根据官方文档是先判断getter方法，按顺序依次从上而下顺序查找方法，获取值，判断是否是集合类型，判断accessInstanceVariablesDirectly是否返回YES,搜索实例变量_, _is, , or is
image.png
image.png
给LGPerson中的实例变量赋值_isName、name、isName赋值后均为null,为什么呢？
image.png
image.png
image.png
因为LGPerson中已经存在_name的实例变量，不会去给_isName、name、isName的实例变量赋值
image.png
若将_name的实例变量注释掉，则对_isName赋值，取值时可以取到
image.png
image.png
5.总结
设值:
1.判断setName,_setName,setIsName方法是否存在
2.不存在，间接访问其他实例变量_name,_isName,name,isName取值
1.判断getter方法getName,name,isName,_name是否存在
2.是否是集合类型
3.是否间接取值:accessInstanceVariablesDirectly
4.对间接变量进行取值_name,_isName,name,isName
6.自定义KVC
- 1.设值:分为5步
// KVC 自定义
// 1: 判断什么 key
if (key == nil || key.length == 0) {
return;
}
// 2: setter set: or _set,
// 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];
// _ _is is
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];
- 2.取值
// 1:刷选key 判断非空
if (key == nil || key.length == 0) {
return nil;
}
// 2:找到相关方法 get countOf objectInAtIndex
// 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 _is is
// _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 @"";