Difference Between Viewdidload and Viewdidappear

Difference between viewDidLoad and viewDidAppear

viewDidLoad is called exactly once, when the view controller is first loaded into memory. This is where you want to instantiate any instance variables and build any views that live for the entire lifecycle of this view controller. However, the view is usually not yet visible at this point.

viewDidAppear is called when the view is actually visible, and can be called multiple times during the lifecycle of a View Controller (for instance, when a Modal View Controller is dismissed and the view becomes visible again). This is where you want to perform any layout actions or do any drawing in the UI - for example, presenting a modal view controller. However, anything you do here should be repeatable. It's best not to retain things here, or else you'll get memory leaks if you don't release them when the view disappears.

See: https://developer.apple.com/documentation/uikit/uiviewcontroller

iOS 7 - Difference between viewDidLoad and viewDidAppear

Please Follow the below View Controller Life Cycle Every Time. You will be amazed with the coding and performance of your application in this manner.

What is the difference between -viewWillAppear: and -viewDidAppear:?

In general, this is what I do:

1. ViewDidLoad - Whenever I'm adding controls to a view that should appear together with the view, right away, I put it in the ViewDidLoad method. Basically, this method is called whenever the view was loaded into memory. So for example, if my view is a form with 3 labels, I would add the labels here; the view will never exist without these forms.

2. ViewWillAppear: I use ViewWillAppear usually just to update the data on the form. So, for the example above, I would use this to actually load the data from my domain into the form. Creation of UIViews is fairly expensive, and you should avoid as much as possible doing that on the ViewWillAppear method because when this gets called, it means that the iPhone is already ready to show the UIView to the user, and anything heavy you do here will impact performance in a very visible manner (like animations being delayed, etc).

3. ViewDidAppear: Finally, I'm using ViewDidAppear to start off new threads to things that would take a long time to execute, like for example doing a web service call to get extra data for the form above. The good thing is that because the view already exists and is being displayed to the user, you can show a nice "Waiting" message to the user while you get the data.

UIViewController viewDidLoad vs. viewWillAppear: What is the proper division of labor?

viewDidLoad is things you have to do once. viewWillAppear gets called every time the view appears. You should do things that you only have to do once in viewDidLoad - like setting your UILabel texts. However, you may want to modify a specific part of the view every time the user gets to view it, e.g. the iPod application scrolls the lyrics back to the top every time you go to the "Now Playing" view.

However, when you are loading things from a server, you also have to think about latency. If you pack all of your network communication into viewDidLoad or viewWillAppear, they will be executed before the user gets to see the view - possibly resulting a short freeze of your app. It may be good idea to first show the user an unpopulated view with an activity indicator of some sort. When you are done with your networking, which may take a second or two (or may even fail - who knows?), you can populate the view with your data. Good examples on how this could be done can be seen in various twitter clients. For example, when you view the author detail page in Twitterrific, the view only says "Loading..." until the network queries have completed.

Difference between viewDidAppear, viewDidLoad in iPhone/iOS?

A UIView object can get loaded into memory and released multiple times without ever getting added to the view stack and appearing on the display.

My guess is that you have 2 references to this view (maybe one in a nib file?), so it's getting loaded, then released when the second reference is loaded and assigned to the same property, then only the latter gets added to the view stack. You can see this by printing out (NSLog) the integer value of self ("%ld",(long int)self) in the viewDidLoad and viewDidAppear methods.

What is better place for loading data from API- viewDidLoad, viewWillAppear or viewDidAppear?

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 vs ViewWillAppear in IOS

viewDidLoad is not called once for the Application. It is get called once for that viewController when the view holds memory and loaded.

So as many number of of time you push to the viewController, that many times it will call the viewDidLoad

• viewDidLoad() — Called when the view controller’s content view (the top
  of its view hierarchy) is created and loaded

• viewWillAppear() — Intended for any operations that you want always to
  occur before the view becomes visible.

For more info about this look at the link : https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/Lesson4.html

So if the view is already in memory (Like your case), then no need to push again, only need to pop back by this code

self.navigationController?.popViewControllerAnimated(true)

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