ios - 当 Controller 被释放时，键值观察者仍然在其中注册

Question

我在代码中添加了一个观察者，然后在 dealloc 和 viewWillDisappear 中将其删除，但我仍然收到错误信息

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'An instance 0x167e5980 of class MyController2 was deallocated while key value observers were still registered with it.

Current observation info: <NSKeyValueObservationInfo 0x16719f90> (
<NSKeyValueObservance 0x16719fb0: Observer: 0x167e5980, Key path: dataContainer.report, Options: <New: YES, Old: YES, Prior: NO> Context: 0x0, Property: 0x1677df30>
)'

我创建了一个 Controller MyController 并从中派生了一个新的 Controller MyController2。现在我在 MyController2 中添加了 KVO。

- (void)viewDidLoad {
    [super viewDidLoad];
    [self addObserver:self forKeyPath:@"dataContainer.report" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
}

然后在 observeValueForKeyPath 中:-

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {

    id oldC = [change objectForKey:NSKeyValueChangeOldKey];
    id newC = [change objectForKey:NSKeyValueChangeNewKey];

    if([keyPath isEqualToString:@"dataContainer.report"]) {
        if (oldC != newC) {
            //Remove Observer

            [self removeObserver:self forKeyPath:@"dataContainer.report" context:nil];
            [self updateDataContainer];
            [self reportView];
        }
    }
}

然后我尝试在 viewWillDisappear 和 dealloc 中删除观察者:-

- (void)dealloc {
    @try{
        [self removeObserver:self forKeyPath:@"dataContainer.report" context:nil];
    }@catch(id anException){
    }
}

-(void) viewWillDisappear:(BOOL)animated{
    @try{
        [self removeObserver:self forKeyPath:@"dataContainer.report" context:nil];
    }@catch(id anException){
    }
    [super viewWillDisappear:animated];
}

我看了 lost of posts ，他们都说一件事你需要删除观察者。我试图从他们两个中删除观察者，但我仍然遇到问题。

Answer 1

根据我的经验，在 iOS 中添加和删除观察者的最佳方式。

在ViewDidLoad中添加观察者:-

- (void)viewDidLoad {
    [super viewDidLoad];
    [self addObserver:self forKeyPath:@"dataContainer.report" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
}

要观察观察者，我们必须这样做:-

Don't remove observer in observeValueForKeyPath

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {

    id oldC = [change objectForKey:NSKeyValueChangeOldKey];
    id newC = [change objectForKey:NSKeyValueChangeNewKey];

    if([keyPath isEqualToString:@"dataContainer.report"]) {
        if (oldC != newC) {
            [self updateDataContainer];
            [self reportView];
        }
    }
}

在 dealloc 中删除观察者:

call remove once here

- (void)dealloc {
    @try{
        [self removeObserver:self forKeyPath:@"dataContainer.report" context:nil];
    }@catch(id anException){
    }
}