#interfacebuilder

Everyone who's ever coded iOS apps with me knows I'm a huge fan of Storyboards, though the one thing which has always annoyed me about it is just how difficult it is to lay out content in a UIScrollView which is larger than the size on screen.  

I was just browsing YouTube, and managed to find this excellent tutorial on how to do just that in Interface Builder.  It goes through laying out content not just for NIBs / XIBs, but also for Storyboards, and there's even a little bit about using Auto Layout too.  (Pro-tip, when using Auto Layout don't forget to pin the first element to the top and left of the scroll view, and the last element to the bottom and right of the scroll view - which is used by Xcode to automatically set the contentSize - so you don't have to).

If you don't have Scroll View problems the video is still worth a watch, if just to learn all the keyboard shortcuts for navigating and manipulating the view hierarchy.

reason: ‘-[UIViewController _loadViewFromNibNamed:bundle:] loaded the “ThirdView” nib but the view outlet was not set.‘

これは、「”ThirdView”をロードしたけど、viewアウトレットが設定されていないよ！」ということなので、先ほど作成した”ThirdView.xib”をダブルクリックし、「File’s Owner」をクリックし、Identity Inspector を開きます。表示されたinspectorの上部にある「Class」という箇所に「FirstViewController」を設定します。

この状態で　File’s Owner を右クリックすると、Outlets の中に view というのがありますので、それと、File’s Owner というオブジェクトが入っているウインドウ内のview とを接続します。

ここまで出来たら、保存します。

I read a piece of advice somewhere that I vaguely remembered but never took much notice of. It was (I think) about weither to use 'retain' or 'assign' for properties and went along these lines, "Use 'retain' because objects from NIB file can get released during low memory conditions". I remembered it but didn't take much notice, mostly because I mainly use properties for floats rather then objects.

An odd thing about testing on newer devices is that because apps you open stay in ram as long as they can you actually get more memory warnings then on older devices. Unless I want to access it from other objects I connect things using IBOutlet 'class' *'object_name'; in the interface declaration, rather then through @property. 1 reason for this was I didn't have to do any memory management for it.

Normally if I use IB (interface builder) I only connect up buttons with actions and don't touch the UI after that. Recently though I was working on a project where I was fiddling with the button's background color as it was pressed to get a nice subtle effect.

When I tested it on the device though I would randomly be getting unexplained crashes, rarely when the same button was pressed as last time.

After lots of bug fixing (which fixed a few other issues as well) a noticed the game always received a Level 2 memory warning just before crashing and that piece of advice I had read popped into the back of my head.

After anding [object retain]; in the -viewDidLoad method and [object release]; in the dealloc method it stopped crashing!

Rule

Yesterday I started to develop an application using PyObjC and The Apple Interface Builder tool. At the beginning it's quite confusing and it has a bit of a learning curve, but after a while, it worth the time spent because you will be developing with Python.

One of the first thing I had to confront was to find a method with the behavior of viewDidAppear. Fortunately I found it, it's called awakeFromNib. So... let's suppose you have a class called LoginController, which will be the representation of the NSObject linked to your view. Well you will have to define the function awakeFromNib inside the class.

At the end, your code should look pretty similar to this:

import objc from Foundation import * class LoginController(NSObject): window = objc.IBOutlet() username_textfield = objc.IBOutlet() password_textfield = objc.IBOutlet() login_button = objc.IBOutlet() def awakeFromNib(self): NSLog("awakeFromNib do whatever you want")