在 viewDidLoad 中加载数据是否太晚而无法在 UIViewController 中显示？

Question

Where do you usually load data when using a UIViewController?

When I say "loading data" I mean: API calls to fetch it and its manipulation.

Do you load it in the view controller initializer, or load it before to initialize it and pass it? Or do you add the code to viewDidLoad?

Also, what about the data for the rootViewController? The one that initialises from storyboard when you launch the app?

Answer 1

Do you load it in the view controller initializer, or load it before to initialize it and pass it? Or do you add the code to viewDidLoad?

Usually this done inisde viewDidLoad ex in MVC you call the controller to load the data and refresh the contents of the vc like table/collection, regarding sending data case this known as dependency injection

Also, what about the data for the rootViewController?

rootViewController is same as any other vc

Answer 2

First of all let me suggest not to have data loading code in ViewController if your app is not very very simple. It would be a better practice to have it in a separate class. Check out MVP or VIPER design patterns for more info.

As for when to load your data (after view loaded or before) is more of a UX decision. If you start loading after, of course, screen might be empty for a while, it would be good to have some loading indicator on the screen so that users do not get confused. Whether users will see empty screens often or not depends on whether you store your loaded data permanently (in a local DB), have some run time cache, or non of that. If you have some caching, empty screen will be visible just once, because if data is loaded and cached you will show that and update the screen after new data is received.

You can also start loading data before view is loaded (in loadView()) or may load some minimal data for the views which are not visible (so that they are not completely empty when opened) and then load full data after view is loaded.

Any approach you choose is highly dependent on what kind of user experience do you want to provide, also on how long it takes to load your data.

Answer 3

Answer in one line is viewididload but below is the actual structural method.

So for this you can have multiple answer the most popular answer for these days would be using MVC/MVVM. So let's discus about MVVM with delegate/protocol

Model - your data.

View model - here you initialize/modify/handle your data.

Viewcontroller - viewdidload - here you can initialize your view model and interact with the data that can be provided by view model with the help of delegate-protocol mechanism.