Hi I have a viewcontroller in a tabview controller. I decided to use NSNotification to flag when views in the tabview controller need to update their data. Previously each had logic to tred to decided the state of the data model and update accordingly.
My update code calls some stuff that in turn call delegate methods. These were all working when not using notification.
My first attempt at notifying seemed to call the selector before the view controller had initialised (before viewDidload at least). Among other thing the delegate methods were never called when the update in the notification selector was run and the view controller didn't get updated. Seems like the viewcontroller is in some unknown state.
I ran a test and put the same update code in the viewDidLoad and only called the notification code after the viewDidLoad had been called. This works.
My question is ,is there another way of preventing the notification selector method being called before viewDidLoad or the object is otherwise correctly initialised.
I am using storyboard so I am not programming the creation of views etc.
I hope this is clear - posting a whole bunch of code would not had been any easier.
Thanks guys, both right! I set up the Notification in app delegate. I should put it at the end of viewDidLoad. Then it is only called when there is a subsequent update and I don't need a flag to stop the first notification from doing an update before the object is up and running.
Related
I am making an IOS app where i am calling an API in viewDidLoad method of view controller. Now i want to reload the same view controller with the data that comes from server. How many ways are there to do this task and what would be the best way?? Please help me.
Thanks!!
viewDidLoad method is called first time when UIViewController is first loaded and when it pop and then you reenter in it at that time viewDidLoad is called. So if you want to load the API only once then viewDidLoad is the best place to call an API.
viewWillAppear called every time when you enter in that UIViewController and it is the place load the API when you want to get refreshed data (updated data).
viewDidAppear also called like viewWillAppear but bit late called than viewWillAppear so if you want to call the API every time than the best place is viewWillAppear method.
Because viewDidAppear method called late from viewWillAppear method and you are just requesting the API so the response of API may be late and If your UI change based on API response then it will stuck the application UI so there is a best place to call API either viewDidLoad & viewWillAppear methods.
viewDidLoad is called once. If you use navigation controller and do back and forth ou view controller this viewDidLoad method will never be called. Until you create this ViewController again (i.e [navContoller pushViewController]). If your api data will never changed the life cycle of this View Controller the this is the better place to call your API. But if your api data need to call frequently [i.e. back and push.forth this view controller] then you should not call api here.
viewWillAppear: before a view controller shows.If you call you api
inside this method you UI will stack until the data loading finish. which looks odd.before load the view of viewController this "viewWillAppear" method is called. This is the reason, it's name is "viewWillAppear". That means this view will load some time later (i.e some micro second later). If you call your api here after what will happen lets analyze. Say, your api return response after 10 sec. Then UI will freeze/stuck for 10 sec and you will see after this 10 sec later your view will called.
viewDidAppear: after finished a view controller showing.So, you need to called your loading API inside this method.
viewDidAppear is definitely not the one you want to use, it will 'pause' the view from responding while you're loading the data.
Normally viewDidLoad is the one you want to place it.
If we stay in the same ViewController,the three method viewdidload,viewwillappear,viewdidappear will not called again.So we stay in the same view controller, we get the data from the server,we should call the reload method after get the data.
Hope this answer can help you.
I think viewWillAppear is best place for loading data from API. Because viewDidLoad called once when the view is being loaded, but viewWillAppear will called when it loaded from its parent view or child view.
You don't need to call API every time you navigate to view controller, you need to call it one time.
If you have a TableView with Cell and this cell get from API and will open new ViewController when you press on it.
So here you will not add your API in :
viewWillAppear()
viewDidAppear()
You will add it one time in viewDidLoad() while we need to minimize num of requests as many as we can.
Example like this: navigation controller:
suppose Fruits and Cars will present from API.
when you click on the fruits cell you will navigate to below viewController:
So when you want to go back to the first view controller, clearly you dont need to reload api while it is already exist.
In this case we use viewDidLoad() to handle API request
I am making an IOS app where i am calling an API in viewDidLoad method of view controller. Now i want to reload the same view controller with the data that comes from server. How many ways are there to do this task and what would be the best way?? Please help me.
Thanks!!
viewDidLoad method is called first time when UIViewController is first loaded and when it pop and then you reenter in it at that time viewDidLoad is called. So if you want to load the API only once then viewDidLoad is the best place to call an API.
viewWillAppear called every time when you enter in that UIViewController and it is the place load the API when you want to get refreshed data (updated data).
viewDidAppear also called like viewWillAppear but bit late called than viewWillAppear so if you want to call the API every time than the best place is viewWillAppear method.
Because viewDidAppear method called late from viewWillAppear method and you are just requesting the API so the response of API may be late and If your UI change based on API response then it will stuck the application UI so there is a best place to call API either viewDidLoad & viewWillAppear methods.
viewDidLoad is called once. If you use navigation controller and do back and forth ou view controller this viewDidLoad method will never be called. Until you create this ViewController again (i.e [navContoller pushViewController]). If your api data will never changed the life cycle of this View Controller the this is the better place to call your API. But if your api data need to call frequently [i.e. back and push.forth this view controller] then you should not call api here.
viewWillAppear: before a view controller shows.If you call you api
inside this method you UI will stack until the data loading finish. which looks odd.before load the view of viewController this "viewWillAppear" method is called. This is the reason, it's name is "viewWillAppear". That means this view will load some time later (i.e some micro second later). If you call your api here after what will happen lets analyze. Say, your api return response after 10 sec. Then UI will freeze/stuck for 10 sec and you will see after this 10 sec later your view will called.
viewDidAppear: after finished a view controller showing.So, you need to called your loading API inside this method.
viewDidAppear is definitely not the one you want to use, it will 'pause' the view from responding while you're loading the data.
Normally viewDidLoad is the one you want to place it.
If we stay in the same ViewController,the three method viewdidload,viewwillappear,viewdidappear will not called again.So we stay in the same view controller, we get the data from the server,we should call the reload method after get the data.
Hope this answer can help you.
I think viewWillAppear is best place for loading data from API. Because viewDidLoad called once when the view is being loaded, but viewWillAppear will called when it loaded from its parent view or child view.
You don't need to call API every time you navigate to view controller, you need to call it one time.
If you have a TableView with Cell and this cell get from API and will open new ViewController when you press on it.
So here you will not add your API in :
viewWillAppear()
viewDidAppear()
You will add it one time in viewDidLoad() while we need to minimize num of requests as many as we can.
Example like this: navigation controller:
suppose Fruits and Cars will present from API.
when you click on the fruits cell you will navigate to below viewController:
So when you want to go back to the first view controller, clearly you dont need to reload api while it is already exist.
In this case we use viewDidLoad() to handle API request
I got two viewcontroller: MainController and OptionsController.
OptionsController it can be reached through a button from MainController.
In OptionsController is there some values that I can save with NSUserDefaults. These values are needed in MainController.
If I change these values in OptionsController when I come back to MainController they don’t change, but if I launch MainController again, these values was changed correctly.
It seems that when MainController becomes active again, after leaving OptionsController, viewDidLoad is no longer raised.
How can I update the data in MainController, please?
As rounak says, viewDidLoad is only called once in the life of a view controller. If you have code you want executed every time a view controller is shown, put it in viewWillAppear.
NSUserDefaultsis a fairly heavyweight way to pass info between in-memory objects (it writes to disk). If you don't need persistence between runs, one of the other options he suggested would be better. I'd suggest the delegate pattern or a completion block.
viewDidLoad is called only once for a view controller. You can use NSNotification, KVO, blocks or something like a delegate pattern to get a callback in your MainController whenever the value changes inside the OptionsController.
You can otherwise write code in viewWillAppear which gets called each time you pop the options controller.
I wonder if dealloc is always called when you close a ViewController in Objective-C for iOS. I've done some tests and it seems like it. Except I don't get any logs when I swipe close the application. I figured that maybe XCode doesn't log things if you fully close the app like that.
The reason I wonder this is because I'm sending analytic data when one of the ViewControllers closes and I kinda need to know if dealloc is always called or if there's any better way doing this.
If you want to get notified when app is killed via Swiping , you can use applicationWillTerminate method and in this method , you can check for current view controller in navigation stack and send analytical data for that View controller .
It's not defined when dealloc will be called for a view controller (or pretty much any class), therefore don't use it for sending analytics.
Use viewDidDisappear instead, which you can rely on to be called when the view controller has been removed.
I have written a piece of code to create a record in Core DB in ViewWillDisappear. but unable to test that on simulator as ViewWillDisappear is never invoked. What kind of operation should i do to invoke it. tried stopping from Xcode no luck.
may be a silly one. but needs pointers.
Thanks.
Doc
says :
This method is called in response to a view being removed from a view hierarchy. This method is called before the view is actually removed and before any animations are configured.
Subclasses can override this method and use it to commit editing changes, resign the first responder status of the view, or perform other relevant tasks. For example, you might use this method to revert changes to the orientation or style of the status bar that were made in the viewDidDisappear: method when the view was first presented. If you override this method, you must call super at some point in your implementation.
You have to pop this view controller from the navigation stack or to push another view controller from it in order to invoke viewWillDissapear