KVO相信大家已经很熟悉了,但是就开发中使用情况来看,KVO有以下的不方便之处:
所有的observe处理都放在一个方法里处理,如果需要监听多个属性就需要判断
添加observe和处理observe的代码过于分散,可读性不好
调用多次相同的removeObserve会导致crash
这里可以利用Runtime来实现一个带block的KVO,这样就把添加observe和处理observe的代码集中起来了,下面看代码
给NSObject写一个KVO的分类,实现自己的监听方法
- (void)xhr_addObserverForKey:(NSString*)key block:(void(^) (NSDictionary*valueInfo))valueChangedBlock;- (void)xhr_removeObserverForKey:(NSString*)key;- (void)xhr_removeAllObserver;
在addObserverForKey方法中实现自己的KVO
根据传进来的key获取setter方法名
//获取setter方法名NSString*selectorName = [NSStringstringWithFormat:@"set%@:",key.capitalizedString];SEL setterSEL =NSSelectorFromString(selectorName);
记录被监听者setter方法IMP指针
//记录被监听者的setter方法的IMP指针MethodsuperSetter = class_getInstanceMethod([selfclass],setterSEL);_VIMP superSetterIMP = (_VIMP)method_getImplementation(superSetter);
获取动态创建的子类的类名
//获取子类的类名NSString*childClassName =NSStringFromClass([selfclass]);if(![childClassName hasPrefix:childClassPrefix]){childClassName = [NSStringstringWithFormat:@"%@%@",childClassPrefix,NSStringFromClass([selfclass])];}else{superSetter = class_getInstanceMethod(class_getSuperclass([selfclass]),setterSEL);}
获取被监听属性的数据类型,根据RunTime的映射来判断
//获取被监听属性的数据类型NSString*methodType = [NSStringstringWithUTF8String:method_getTypeEncoding(superSetter)];//NSLog(@"%@",methodType);//v20@0:8i16 //methodType = [methodType componentsSeparatedByString:@"@0:8"].lastObject;NSString*valueType = [methodType substringToIndex:methodType.length-2];
动态地创建类继承自被监听者
//判断需要创建的类是否存在 objc_getClassClassChildClass= objc_getClass(childClassName.UTF8String);if(!ChildClass) {//创建类ChildClass= objc_allocateClassPair([selfclass],childClassName.UTF8String, 0);//注册类objc_registerClassPair(ChildClass); }
改变self的isa指针
//使当前类的isa指针指向新创建的类object_setClass(self, ChildClass);
根据key的不同类型来重写子类的setter方法
IMP childSetValue =nil;if([valueType isEqualToString:[NSStringstringWithUTF8String:@encode(int)]]) { childSetValue = imp_implementationWithBlock(^(id_self,intnewValue) {//调用被监听对象(父类)的setter方法给被监听者属性赋值//@"こうさか ほのか"(*superSetterIMP)(_self,setterSEL,newValue);idoldValue = objc_getAssociatedObject(weakself, key.UTF8String); objc_setAssociatedObject(weakself, key.UTF8String, @(newValue), OBJC_ASSOCIATION_RETAIN_NONATOMIC);if(!oldValue) { oldValue = [NSNullnull]; }NSDictionary*valueInfoDictionary = @{@"oldValue":oldValue,@"newValue":@(newValue)}; !valueChangedBlock?:valueChangedBlock(valueInfoDictionary); }); }
添加setter方法
//给子类添加setter方法class_replaceMethod(ChildClass, setterSEL, childSetValue, [NSStringstringWithFormat:@"v@:%@",valueType].UTF8String);
移除监听
(void)xhr_removeAllObserver,这个简单,就是移除所有子类的关联,改变isa指针指向父类
if(![NSStringFromClass([selfclass])hasPrefix:childClassPrefix])return;objc_removeAssociatedObjects(self);object_setClass(self, class_getSuperclass([selfclass]));
(void)xhr_removeObserverForKey:(NSString *)key,这个就得判断调用的类是不是子类,如果不是就直接返回,防止重复移除导致的crash,如果监听者数组中没有需要监听的key,就直接移除所有,不然self的isa指针还是指向子类
if(![NSStringFromClass([selfclass]) hasPrefix:childClassPrefix])return; XHRKVOAssistClass *KVOAssistInstance = objc_getAssociatedObject(self, XHRKVOAssistInstance);/**
* 防止重复移除监听
*/if(!KVOAssistInstance.observerKeyArray.count) { [selfxhr_removeAllObserver];return; }//获取被监听者的类Class superClass = class_getSuperclass([selfclass]);//获取setter方法名NSString*selectorName = [NSStringstringWithFormat:@"set%@:",key.capitalizedString]; IMP superSetterIMP = class_getMethodImplementation(superClass,NSSelectorFromString(selectorName));//获取被监听key属性的数据类型NSString*methodType = [NSStringstringWithUTF8String:method_getTypeEncoding(class_getInstanceMethod(superClass,NSSelectorFromString(selectorName)))]; methodType = [methodType componentsSeparatedByString:@"@0:8"].lastObject;NSString*valueType = [methodType substringToIndex:methodType.length-2]; class_replaceMethod([selfclass],NSSelectorFromString(selectorName), superSetterIMP, [NSStringstringWithFormat:@"v@:%@",valueType].UTF8String); [KVOAssistInstance.observerKeyArrayremoveObject:@{valueType:key}];//判断移除后数组是否为空,为空即移除所监听if(!KVOAssistInstance.observerKeyArray.count) { [selfxhr_removeAllObserver];return; }
注意事项：
1.addObserver的blcok里面如果需要用到self必须使用weakself
2.不能使用在同一个类的不同对象的同一个属性的监听
