我正在开发一个测试应用程序,其中有一个 NSOperationQueue。我正在创建一个 NSInvocationOperation 并观察该操作的“isFinished”属性。 奇怪的是,observeValueForKeyPath 只是有时被调用。我无法理解每次调用它时必须进行的更改。请帮忙。
这是我写的代码:
-(BOOL)applicationUIApplication *)application didFinishLaunchingWithOptionsNSDictionary *)launchOptions
{
........//initialization
queue = [NSOperationQueue new];
operation=[NSInvocationOperation new];
operation = [[NSInvocationOperation alloc]initWithTarget:self selectorselector(CreateOperationWithContext object:context];
[operation addObserver:self forKeyPath"isFinished" optionsNSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:NULL];
[queue addOperationperation];
..... // launch the view controller
}
-(void)observeValueForKeyPathNSString *)keyPath ofObjectid)object changeNSDictionary *)change contextvoid *)context
{
if ([keyPath isEqualToString"isFinished"]) {
NSLog(@"came in");
[operation removeObserver:self forKeyPath"isFinished"];
}
else
{
[super observeValueForKeyPath:keyPath ofObjectbject change:change context:context];
}
}
以下代码对我有用。我从 iOS 单 View 应用程序模板开始。这是我所拥有的:
@implementation SOAppDelegate
{
NSOperationQueue* queue;
NSOperation* operation;
}
- (void)CreateOperationWithContext: (id)foo
{
NSLog(@"Op ran");
}
- (BOOL)applicationUIApplication *)application didFinishLaunchingWithOptionsNSDictionary *)launchOptions
{
queue = [NSOperationQueue new];
// operation = [NSInvocationOperation new]; // Commented this out because it's redundant with the next line
operation = [[NSInvocationOperation alloc] initWithTarget:self selectorselector(CreateOperationWithContext object:[NSObject new]];
[operation addObserver:self forKeyPath"isFinished" optionsNSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:NULL];
[queue addOperationperation];
return YES;
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if ([keyPath isEqualToString"isFinished"])
{
NSLog(@"came in");
[operation removeObserver:self forKeyPath"isFinished"];
}
else
{
[super observeValueForKeyPath:keyPath ofObjectbject change:change context:context];
}
}
// ... rest of empty default app delegate methods here...
@end
在控制台中,我看到:
2013-08-13 08:04:15.150 TestOpKVO[71373:20b] Op ran
2013-08-13 08:04:21.903 TestOpKVO[71373:20b] came in
所以关于您的 -CreateOperationWithContext:
实现的某些问题正在引起麻烦。也就是说,即使我将操作更改为引发异常,我仍然会看到 KVO 通知被调用。
如果我是你,我会从这个非常基本的、有效的示例开始,然后一步一步调整它以适应你的真实代码,检查每一步以确保通知仍然有效。
一些提示:(可能与您看到的问题无关,但使用 KVO 的良好做法)
首先,在您的观察中使用 KVO 上下文。它更安全,更具确定性。见 answer I wrote over here了解详情。
其次,不要从 -observeValueForKeyPath:
(或 -addObserver:...
的调用中调用 -removeObserver:forKeyPath:
> 任一)对于被通知的相同 keyPath。这有可能弄乱 KVO 的内部观察者数据结构,并可能导致非确定性崩溃,让您抓狂。见 answer I wrote over here了解详情。
关于ios - observeValueForKeyPath 没有被调用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18189035/
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