key-value-observing

问题 I am using AVFoundation in iOS to manipulate the torch on an iPhone 6. I need to know the current torch level. I've read in AppleDevLib that it's possible to observe the current torch level using KVO, but I've failed to implement that. Can you put down some sample that detect change of torch level and then changes a variable (like label on screen etc.) please? It will help me a lot. 回答1: It took a while for me to figure out how to do this but I believe this KVO code will work for you. I haven

问题 I have observers added to several NSTextFields to monitor changes in each text field. The key of each text field is configured in Interface Builder at Bindings -> Value -> Model Key Path . When the number in one text field is changed, the other text fields automatically update their value. Since an observer was added to each text field, I must remove the other observers to avoid a loop that will crash the app. After the observers are removed, I must add them back to the other text fields so

问题 I have observers added to several NSTextFields to monitor changes in each text field. The key of each text field is configured in Interface Builder at Bindings -> Value -> Model Key Path . When the number in one text field is changed, the other text fields automatically update their value. Since an observer was added to each text field, I must remove the other observers to avoid a loop that will crash the app. After the observers are removed, I must add them back to the other text fields so

问题 I have a "scrollview" with nodes ( UIViews ) that can be dragged around. I am trying to draw edges between selected UIViews with a "calayer", but I can't figure out how to redraw the line when a views position have changed. In my viewController class I add the edge between first and second in the nodes array as: EdgeLayer *edge = [[EdgeLayer alloc]init]; edge.delegate = self; edge.strokeColor = [UIColor colorWithWhite:0.25 alpha:1.0]; edge.strokeWidth = 0.5; edge.startNode = [nodes

问题 I'm trying to observe checkbox status and make appropriate changes in the app when checkbox status changes. In a window manager that manages the window with checkbox I have following observer setup: - (void)awakeFromNib { [myCheckBox addObserver:self forKeyPath:@"state" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld) context:NULL]; } - (void)dealloc { [myCheckBox removeObserver:self forKeyPath:@"state"]; } - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id

问题 Im trying to subclass a NSOperation, and read some sample from, they say: when the task finished, using KVO of NSOperation, to finish the operation, code here: [self willChangeValueForKey:@"isFinished"]; [self willChangeValueForKey:@"isExecuting"] finished = YES; executing = NO; [self didChangeValueForKey:@"isFinished"]; [self didChangeValueForKey:@"isExecuting"]; then isFinished get called - (BOOL) isFinished{ return(finished); } anyone could explain this to me? why isFinished gets called,

问题 I am registering an observer on a bunch of tableview controllers dynamically so I need to remove previous observers if they were registered on the same object. To do this I need to check if the observer exists on the object. Is this possible? I know with NSNotification you can use the NSNotification center singleton but is this the same for KVO? 回答1: No, there is no simple way that I'm aware of. KVO and NSNotification differs in that matter. Why don't you implement your solution with

问题 UIButton has a state property, which appears to be KVO compliant by all accounts and there is no documentation to indicate otherwise. However, when I added an observer to a UIButton's state property, the observer callback was never invoked. How come? 回答1: If you look at the documentation of UIControl, the state property is marked: synthesized from other flags. I guess this is why changes to this property are not KVO compliant. However, you can simply register and observer for the values you

问题 I'm trying to use KVO in Swift, but the method "observeValueForKeyPath" is called once. Here's a GIST of my code I tried to use NSNumber instead of Int , add all options to addObserver , but the method is still call once when my view load. Any idea ? EDIT: It seems like I found a temporary solution using: var lifes: Int { willSet { willChangeValueForKey("lifes") } } 回答1: KVO requires dynamic dispatch, so the dynamic modifier needs to be added to the property: dynamic var lifes = 0 来源： https:/

问题 Perfect KVO here includes two parts: add observer correctly and remove observer correctly. The story: I use one UITableViewCell(cell) to display one NSManagedObject(object). Each object has some dynamic properties that need observing by its cell. Not all objects have the same set of observed properties. I add key path observers selectively like this: if (object.thumbnail_pic_url) [object addObserver:cell forKeyPath:@"thumbnail_picture" options:0 context:NULL]; Object could be deleted. I must