手动 触发 kvo

手动 触发 kvo

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过程如下：

1. 重写automaticallyNotifiesObserversForKey 返回 NO
2. 非可变容器属性 在 set 中 添加方法 willChangeValueForKey,didChangeValueForKey
3. 可变容器属性根据 kvc 创建 代理对象，并在里面调用方法 willChange:valuesAtIndexes:forKey:, didChange:valuesAtIndexes:forKey:
4. kvo 响应方法 observeValueForKeyPath:ofObject:change:context:.

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具体过程

1. 重新方法 automaticallyNotifiesObserversForKey , 对需要手动控制 kvo 的 key 返回 NO
   我们把 属性 name, number, arr, mutableArr 都设为手动触发 kvo

    + (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key{
        BOOL automatic = NO;
        if ([key isEqualToString:@"name"]) {
            automatic = NO;
        }else if ([key isEqualToString:@"number"]){
            automatic = NO;
        }else if ([key isEqualToString:@"arr"]){
            automatic = NO;
        }else if ([key isEqualToString:@"mutableArr"]){
            automatic = NO;
        }else {
            automatic = [super automaticallyNotifiesObserversForKey:key];
        }
        return automatic;
    }

2. 在属性 set 方法中手动触发 kvo, willChangeValueForKey, didChangeValueForKey

    // 手动改管理 kvo 触发，有个明显的好处，就是，我们在不需要触发kvo时可以很容易的停止触发，如下
    // 当 name 在设值 前和 设值后 是一样的比如都是 王小小，我们就可以不触发kvo
    // 如果是 自动 kvo 就无法达到这样的控制效果。
    - (void)setName:(NSString *)name{
    if (![_name isEqualToString:name]) {
        [self willChangeValueForKey:@"name"];
        _name = name;
        [self didChangeValueForKey:@"name"];
        }
    }
    // 设值 kvo 触发条件， 只有当 bunber > 10 的时候，才会触发 kvo。
    - (void)setNumber:(int)number{
        if (number>10) {
            [self willChangeValueForKey:@"number"];
            _number = number;
            [self didChangeValueForKey:@"number"];
        }
    }

    - (void)setArr:(NSArray *)arr{
        [self willChangeValueForKey:@"arr"];
        _arr = arr;
        [self didChangeValueForKey:@"arr"];
    }

3. 在可变容器中触发 kvo， 结合 kvc 可变容器代理对象创建。
   需要实现一对删除和插入的方法, 并在这些方法中调用方法 willChange:valuesAtIndexes:forKey:, didChange:valuesAtIndexes:forKey:

        // 可变容器添加手动kvo，可变容器内部元素发生添加，移除，替换时触发kvo
        // 插入单个 元素
        - (void)insertObject:(NSString *)object inMutableArrAtIndex:(NSUInteger)index{
            [self willChange:NSKeyValueChangeInsertion valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutableArr"];
            [_mutableArr insertObject:object atIndex:index];
             [self didChange:NSKeyValueChangeInsertion valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutableArr"];
        }

        // 删除 单个元素
        - (void)removeObjectFromMutableArrAtIndex:(NSUInteger)index{
            [self willChange:NSKeyValueChangeRemoval valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutableArr"];
            [_mutableArr removeObjectAtIndex:index];
            [self didChange:NSKeyValueChangeRemoval valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutableArr"];
        }
        // 插入 多个元素
        - (void)insertMutableArr:(NSArray *)array atIndexes:(NSIndexSet *)indexes{
            [self willChange:NSKeyValueChangeInsertion valuesAtIndexes:indexes forKey:@"mutableArr"];
            [_mutableArr insertObjects:array atIndexes:indexes];
            [self didChange:NSKeyValueChangeInsertion valuesAtIndexes:indexes forKey:@"mutableArr"];
        }
        // 删除多个元素
        - (void)removeMutableArrAtIndexes:(NSIndexSet *)indexes{
            [self willChange:NSKeyValueChangeRemoval valuesAtIndexes:indexes forKey:@"mutableArr"];
            [_mutableArr removeObjectsAtIndexes:indexes];
            [self didChange:NSKeyValueChangeRemoval valuesAtIndexes:indexes forKey:@"mutableArr"];
        }
        // 替换 单个
        - (void)replaceObjectInMutableArrAtIndex:(NSUInteger)index withObject:(id)object{
            [self willChange:NSKeyValueChangeReplacement valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutableArr"];
            [_mutableArr replaceObjectAtIndex:index withObject:object];
            [self didChange:NSKeyValueChangeReplacement valuesAtIndexes:[NSIndexSet indexSetWithIndex:index] forKey:@"mutableArr"];
        }
        // 替换 多个
        - (void)replaceMutableArrAtIndexes:(NSIndexSet *)indexes withMutableArr:(NSArray *)array{
            [self willChange:NSKeyValueChangeReplacement valuesAtIndexes:indexes forKey:@"mutableArr"];
            [_mutableArr replaceObjectsAtIndexes:indexes withObjects:array];
            [self didChange:NSKeyValueChangeReplacement valuesAtIndexes:indexes forKey:@"mutableArr"];
        }

外部调用

    // 必须通过 kvc 拿到 属性
    NSMutableArray *mutableArr = [obj mutableArrayValueForKey:@"mutableArr"];
    // 添加一个元素
    [mutableArr addObject:@"100"];
    // 删除一个元素
    [mutableArr removeObjectAtIndex:0];
    // 添加多个元素
    [mutableArr addObjectsFromArray:@[@"90",@"91"]];
    // 删除多个元素
    [mutableArr removeObjectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 2)]];
    // 替换一个元素
    [mutableArr replaceObjectAtIndex:0 withObject:@"替换"];
    // 替换多个元素
    NSArray *objs = @[@"替换: 1",@"替换: 2"];
    [mutableArr replaceObjectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, objs.count)] withObjects:objs];

4. observeValueForKeyPath 响应
   • change 参数：这是一个字典里面包含的key 有
     kind: NSKeyValueChange，跟 willChangeValueForKey 中的保持一致
     indexes: String, 元素变更的位置或者 range
     new: 设值的新值
     old: 之前的旧值

• 代码地址