在导航到ViewController之前为它加载数据的最佳方法是什么？

Question

In my application there are two view controllers that navigate to a DetailsViewController.

Right now, when the DetailsViewController appears, I fetch data from the server and display it on the UI. I dislike this because the UI is blank while the network request is going on. What I want is that the data be loaded in the previous view controllers and then passed to DetailsViewController.

Now the problem is that I have the exact same "load-data-and-then-push" code in two view controllers and I'm not sure what the most sensible way is to remove the repetition.

One idea is to have the two view controllers inherit from a common superclass which contains the loading/pushing method. I don't like this strategy because, supposing I have more ViewControllers like DetailsViewController down the line, I wouldn't like to write a loading superclass for each one.

Another idea would be to define a static method in the DetailsViewController which the two view controllers can invoke but this method contains UI related code (specifically, code to show an HUD Progressbar and a UIAlertView in case network fetch fails) which makes me uncomfortable.

I am very new to iOS and Objective-C so I might be missing something simple and obvious.

Answer 1

My favorite would be in this case to create a new class which handles the loading of the data (like http-request, etc.) and to create a delegate protocol for this class. This delegate callback might then be implemented in your two viewControllers which would then perform the push segue to your DetailsViewController when called. Delegation is a very nice and powerful feature, check out the documentation here: Delegation

Answer 2

Well, I'd better write it in the comments, but I have no reputation for that.

Imagine you are reading a json with several students information (name, year, etc.) you can create a student object with the property that will be read and an object that will have a method that will run in the background that will be responsible for accessing your WS (JSON or whatever it is) and record this information to the student object. So if you have 10 students you will have an NSArray containing 10 students. This array is what you will for your next viewcontroller.

It is a lot of code, but you think examples easily.

Answer 3

If you use Storyboards you can use prepareForSegue: sender: to pass your data/model class to your DetailsViewController. If you use xib's you can do the same after instantiating the DetailsViewController and before pushing it.

If you need to load subsequent data from your server you should write a class that does this network stuff for you.

If DetailsViewController needs to load some additional data, you can use something like a loading view like Andy suggested. This is a widely used method.