如何使用Core Data预加载数据

Question

I created a core data app for the first time. It's running good. I created all my objects with data with a web service (with AFNetworking). My objects are all built. So, now I want to know what is the best way to preload data. (webservice>Core data>My views) For the time being, it's simple but absolutely no user-friendly and that is this :

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [ManagedMember loadDataFromWebService];
    [ManagedLesson loadDataFromWebService];
    [ManagedThematic loadDataFromWebService];
    [ManagedNew loadDataFromWebService];
    [ManagedProject loadDataFromWebService];

    return YES;
}

loadDataFromWebService is a function which call two consecutive functions. (Delete all data in Core data objects and re-create objects which working well) So, I want to know where I can call this 5 functions ? Is it possible to have a loader in the splash screen like many iOS apps ? Or created an intermediate view which load the data.
Many thanks.

Answer 1

Never, never, ever load data like this in didFinishLaunchingWithOptions: . This method should do the minimum necessary and then return, as quickly as possible. Putting slow stuff there can cause a bad user experience, and iOS can shut your app down forcibly if it doesn't exit that function quickly enough.

As D-eptdeveloper suggests, viewDidLoad is a better place to trigger loading code, but it's still not great. Ideally, you trigger your data loading somewhere early on in the app, and individual view controllers just request the data as necessary (with the understanding that the data might not be available yet, and so might have to show some sort of progress indicator).

A suitable place/time to trigger data loading is after the initial UI has been shown to the user. This reduces the potential problem whereby triggering data loading at an earlier time actually slows down the appearance of the UI (not a good user experience).

Answer 2

It's ok to trigger syncing in the AppDelegate (in the applicationDidBecomeActive: method), because it's the first place where your code is executed. Just make sure you do all the syncing in a background thread.

This topic is quite general, but you can find good examples about sync strategies online, eg How To Synchronize Core Data with a Web Service – Part 1 .