R – IPhone – Which View Controller methods to use

cocoa-touchdesign-patternsiphoneuiviewcontroller

I'm trying to figure out what logic should go into the different UIViewController methods like viewDidLoad, viewDidAppear, viewWillAppear, …

The structure of my app is that I have a root view controller that doesn't really have a view of its own, rather it has a tab view controller and loads other view controllers into it. But in the future, it may have to load other view controllers instead of the tab bar controller depending on app logic.

My main question is, what do people usually put into the viewDidLoad, …. methods.

Currently I:

viewDidLoad – setup the tab bar controller and set its view to the view controller's own view

viewDidAppear – check if user has stored login info
if not – present with login
if so, login and get app data for first tab

I'm trying to figure out now if my logic for setting up my tab bar controller should go into loadView rather than viewDidLoad.

Any help would be great. Small examples found on the web are great, but they don't go into detail on how larger apps should be structured.

Best Answer

You should not implement both -viewDidLoad and -loadView; they are for different purposes. If you load a NIB, you should implement -viewDidLoad to perform any functions that need to be done after loading the NIB. Wiring up the tabbar is appropriate there if you haven't already done it in the NIB.

-loadView should be implemented if you do not use a NIB, and should construct the view.

-viewWillAppear is called immediately before you come onscreen. This is a good place to set up notification observations, update your data based on model classes that have changed since you were last on screen, and otherwise get your act together before the user sees you. You should not perform any animations here. You're not on the screen; you can't animate. I see a lot of animation glitches due to this mistake. It kind of works, but it looks weird.

-viewDidAppear is called after you come onscreen. This is where you do any entry animations (sliding up a modal, for instance; not that you should do that very often, but I was just looking at some code that did).

-viewWillDisappear is called right before you go offscreen. This is where you can do any leaving animations (including unselecting tableview cells and the like).

-viewDidDisappar is called after you're offscreen (and the animations have finished). Tear down any observations here, free up memory if possible, go to sleep as best you can.

I touch on setting up and tearing down observations here. I go into that in more depth in View controllers and notifications.

Related Solutions

Ios – How to develop for iPhone using a Windows development machine

It's certainly possible to develop on a Windows machine, in fact, my first application was exclusively developed on the old Dell Precision I had at the time :)

There are three routes;

Install OSx86 (aka iATKOS / Kalyway) on a second partition/disk and dual boot.
Run Mac OS X Server under VMWare (Mac OS X 10.7 (Lion) onwards, read the update below).
Use Delphi XE4 and the macincloud service. This is a commercial toolset, but the component and lib support is growing.

The first route requires modifying (or using a pre-modified) image of Leopard that can be installed on a regular PC. This is not as hard as you would think, although your success/effort ratio will depend upon how closely the hardware in your PC matches that in Mac hardware - e.g. if you're running a Core 2 Duo on an Intel Motherboard, with an NVidia graphics card you are laughing. If you're running an AMD machine or something without SSE3 it gets a little more involved.

If you purchase (or already own) a version of Leopard then this is a gray area since the Leopard EULA states you may only run it on an "Apple Labeled" machine. As many point out if you stick an Apple sticker on your PC you're probably covered.

The second option is more costly. The EULA for the workstation version of Leopard prevents it from being run under emulation and as a result, there's no support in VMWare for this. Leopard server, however, CAN be run under emulation and can be used for desktop purposes. Leopard server and VMWare are expensive, however.

If you're interested in option 1) I would suggest starting at Insanelymac and reading the OSx86 sections.

I do think you should consider whether the time you will invest is going to be worth the money you will save though. It was for me because I enjoy tinkering with this type of stuff and I started during the early iPhone betas, months before their App Store became available.

Alternatively, you could pick up a low-spec Mac Mini from eBay. You don't need much horsepower to run the SDK and you can always sell it on later if you decide to stop development or buy a better Mac.

Update: You cannot create a Mac OS X Client virtual machine for OS X 10.6 and earlier. Apple does not allow these Client OSes to be virtualized. With Mac OS X 10.7 (Lion) onwards, Apple has changed its licensing agreement in regards to virtualization. Source: VMWare KnowledgeBase

Ios – iPhone SDK: what is the difference between loadView and viewDidLoad

I can guess what might be the problem here, because I've done it:

I've found that often when I add init code to loadView, I end up with an infinite stack trace

Don't read self.view in -loadView. Only set it, don't get it.

The self.view property accessor calls -loadView if the view isn't currently loaded. There's your infinite recursion.

The usual way to build the view programmatically in -loadView, as demonstrated in Apple's pre-Interface-Builder examples, is more like this:

UIView *view = [[UIView alloc] init...];
...
[view addSubview:whatever];
[view addSubview:whatever2];
...
self.view = view;
[view release];

And I don't blame you for not using IB. I've stuck with this method for all of Instapaper and find myself much more comfortable with it than dealing with IB's complexities, interface quirks, and unexpected behind-the-scenes behavior.

Best Answer

Related Solutions

Ios – How to develop for iPhone using a Windows development machine

Ios – iPhone SDK: what is the difference between loadView and viewDidLoad

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