UIViewController viewDidLoad vs viewWillAppear What is the proper division of labor

Question

I have always been a bit unclear on the type of tasks that should be assigned to viewDidLoad vs  viewWillAppear  in a UIViewController subclass    e g  I am doing an app where I have a UIViewController subclass hitting a server  getting data  feeding it to a view and then displaying that view  What are the pros and cons of doing this in viewDidLoad vs  viewWillAppear

User · Answer

It s important to note that using viewDidLoad for positioning is a bit risky and should be avoided since the bounds are not set  this may cause unexpected results  I had a variety of issues      This post describes quite well the different methods and what happens in each of them   currently for one-time init and positioning I m thinking of using viewDidAppear with a flag  if anyone has any other recommendation please let me know

User · Answer

Depends  Do you need the data to be loaded each time you open the view  or only once      Red   They don t require to change every time  Once they are loaded they stay as how they were  Purple  They need to change over time or after you load each time  You don t want to see the same 3 suggested users to follow  it needs to be reloaded every time you come back to the screen  Their photos may get updated    you don t want to see a photo from 5 years ago      viewDidLoad  Whatever processing you have that needs to be done once  viewWilLAppear  Whatever processing that needs to change every time the page is loaded   Labels  icons  button titles or most dataInputedByDeveloper usually don t change  Names  photos  links  button status  lists  input Arrays for your tableViews or collectionView  or most dataInputedByUser usually do change

User · Answer

Initially used only ViewDidLoad with tableView  On testing with loss of Wifi  by setting device to airplane mode  realized that the table did not refresh with return of Wifi  In fact  there appears to be no way to refresh tableView on the device even by hitting the home button with background mode set to YES in -Info plist   My solution    - void  viewWillAppear   BOOL  animated    self tableView reloadData

User · Answer

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

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

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