KVO原理分析及使用进阶
该文章属于<简书 — 刘小壮>原创，转载请注明：<简书 — 刘小壮> https://www.jianshu.com/p/badf5cac0130 我们在工作中经常会用到
概述
基础使用使用
注册方法在注册观察者时，可以传入 还可以通过方法 在调用 监听方法观察者需要实现
如果被观察对象是集合对象，在 兼容的调用方式调用 // 直接调用set方法，或者通过属性的点语法间接调用 [account setName:@"Savings"]; // 使用KVC的setValue:forKey:方法 [account setValue:@"Savings" forKey:@"name"]; // 使用KVC的setValue:forKeyPath:方法 [document setValue:@"Savings" forKeyPath:@"account.name"]; // 通过mutableArrayValueForKey:方法获取到代理对象，并使用代理对象进行操作 Transaction *newTransaction = <#Create a new transaction for the account#>; NSMutableArray *transactions = [account mutableArrayValueForKey:@"transactions"]; [transactions addObject:newTransaction]; 实际应用
注意点
苹果官方推荐的方式是，在 手动调用KVO
- (void)setBalance:(double)theBalance {
if (theBalance != _balance) {
[self willChangeValueForKey:@"balance"];
_balance = theBalance;
[self didChangeValueForKey:@"balance"];
}
}
可以看到调用 如果想控制当前对象的自动调用过程，也就是由上面两个方法发起的 + (BOOL)automaticallyNotifiesObserversForKey:(NSString *)theKey {
BOOL automatic = NO;
if ([theKey isEqualToString:@"balance"]) {
automatic = NO;
}
else {
automatic = [super automaticallyNotifiesObserversForKey:theKey];
}
return automatic;
}
实现原理
测试代码为了测试 @interface KVOObject : NSObject
@property (nonatomic,copy ) NSString *name;
@property (nonatomic,assign) NSInteger age;
@end
@implementation KVOObject
- (NSString *)description {
NSLog(@"object address : %p n",self);
IMP nameIMP = class_getMethodImplementation(object_getClass(self),@selector(setName:));
IMP ageIMP = class_getMethodImplementation(object_getClass(self),@selector(setAge:));
NSLog(@"object setName: IMP %p object setAge: IMP %p n",nameIMP,ageIMP);
Class objectMethodClass = [self class];
Class objectRuntimeClass = object_getClass(self);
Class superClass = class_getSuperclass(objectRuntimeClass);
NSLog(@"objectMethodClass : %@,ObjectRuntimeClass : %@,superClass : %@ n",objectMethodClass,objectRuntimeClass,superClass);
NSLog(@"object method list n");
unsigned int count;
Method *methodList = class_copyMethodList(objectRuntimeClass,&count);
for (NSInteger i = 0; i < count; i++) {
Method method = methodList[i];
NSString *methodName = NSStringFromSelector(method_getName(method));
NSLog(@"method Name = %@n",methodName);
}
return @"";
}
在另一个类中分别创建两个 @property (nonatomic,strong) KVOObject *object1; @property (nonatomic,strong) KVOObject *object2; self.object1 = [[KVOObject alloc] init]; self.object2 = [[KVOObject alloc] init]; [self.object1 description]; [self.object2 description]; [self.object1 addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil]; [self.object1 addObserver:self forKeyPath:@"age" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil]; [self.object1 description]; [self.object2 description]; self.object1.name = @"lxz"; self.object1.age = 20; 下面是 // 第一次 object address : 0x604000239340 object setName: IMP 0x10ddc2770 object setAge: IMP 0x10ddc27d0 objectMethodClass : KVOObject,ObjectRuntimeClass : KVOObject,superClass : NSObject object method list method Name = .cxx_destruct method Name = description method Name = name method Name = setName: method Name = setAge: method Name = age object address : 0x604000237920 object setName: IMP 0x10ddc2770 object setAge: IMP 0x10ddc27d0 objectMethodClass : KVOObject,superClass : NSObject object method list method Name = .cxx_destruct method Name = description method Name = name method Name = setName: method Name = setAge: method Name = age // 第二次 object address : 0x604000239340 object setName: IMP 0x10ea8defe object setAge: IMP 0x10ea94106 objectMethodClass : KVOObject,ObjectRuntimeClass : NSKVONotifying_KVOObject,superClass : KVOObject object method list method Name = setAge: method Name = setName: method Name = class method Name = dealloc method Name = _isKVOA object address : 0x604000237920 object setName: IMP 0x10ddc2770 object setAge: IMP 0x10ddc27d0 objectMethodClass : KVOObject,superClass : NSObject object method list method Name = .cxx_destruct method Name = description method Name = name method Name = setName: method Name = setAge: method Name = age 我们发现对象被 在上面的代码中还发现了 重写setter方法
object_getClass为什么上面调用 调用 由此可以推测， typedef struct objc_class *Class;
struct objc_class {
Class _Nonnull isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
Class _Nullable super_class OBJC2_UNAVAILABLE;
const char * _Nonnull name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
struct objc_ivar_list * _Nullable ivars OBJC2_UNAVAILABLE;
struct objc_method_list * _Nullable * _Nullable methodLists OBJC2_UNAVAILABLE;
struct objc_cache * _Nonnull cache OBJC2_UNAVAILABLE;
struct objc_protocol_list * _Nullable protocols OBJC2_UNAVAILABLE;
#endif
}
缺点苹果提供的 在调用 NSStringFromSelector(@selector(isFinished))
自己实现KVO除了上面的缺点， self.object1 = [[KVOObject alloc] init];
[self.object1 lxz_addObserver:self originalSelector:@selector(name) callback:^(id observedObject,NSString *observedKey,id oldValue,id newValue) {
// callback
}];
self.object1.name = @"lxz";
[self.object1 lxz_removeObserver:self originalSelector:@selector(name)];
调用代码很简单，直接通过 通过 如果重复 注意需要注意的是， KVOController想在项目中安全便捷的使用 源码分析从源码来看还是比较简单的，主要分为
在 - (FBKVOController *)KVOControllerNonRetaining
{
id controller = objc_getAssociatedObject(self,NSObjectKVOControllerNonRetainingKey);
if (nil == controller) {
controller = [[FBKVOController alloc] initWithObserver:self retainObserved:NO];
self.KVOControllerNonRetaining = controller;
}
return controller;
}
FBKVOController部分在 还有一个私有类 其功能很简单，通过 在外界使用时需要用 使用 - (void)_observe:(id)object info:(_FBKVOInfo *)info
{
NSMutableSet *infos = [_objectInfosMap objectForKey:object];
_FBKVOInfo *existingInfo = [infos member:info];
if (nil != existingInfo) {
return;
}
if (nil == infos) {
infos = [NSMutableSet set];
[_objectInfosMap setObject:infos forKey:object];
}
[infos addObject:info];
[[_FBKVOSharedController sharedController] observe:object info:info];
}
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