How do you check to see if a variable has changed every second or less in objective c?
I am using an if statement to check th开发者_开发知识库e value of a BOOLEAN when i click on a button. When the button is clicked if the value is false i want to display a UIActivityIndicator and if the value is true i want to push the new view. I can do this fine but i want the view to change automatically when the BOOLEAN Becomes true if the user has already clicked the button.
So my question is how do you check to see if a value has changed everysecond or less?
Look into KVO — Key-Value Observing — to trigger an action when a variable changes its value.
In your view controller's -viewWillAppear:
method, for example, add the observer:
[self addObserver:self forKeyPath:@"myBoolean" options:NSKeyValueObservingOptionNew context:nil];
In your -viewWillDisappear:
method, unregister the observer:
[self removeObserver:self forKeyPath:@"myBoolean"];
It's important to do this last step, so that the -dealloc
method doesn't throw an exception.
Finally, set up the observer method to do something when there is a change to myBoolean
:
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if ([keyPath isEqual:@"myBoolean"]) {
// The BOOL value of myBoolean changed, so do something here, like check
// what the new BOOL value is, and then turn the indicator view on or off
}
}
The Key-Value Observing pattern is a good, general way to trigger something when an object's value changes somewhere. Apple has written a good "quick-start" document that introduces this topic.
Have a look a Key-Value Observing (often referred to simply as KVO). It uses the language's dynamic introspective capabilities to implement exactly this functionality for you.
I think you want to look into the Observer Pattern.
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