I previously explained how to use NSUserDefaults to your advantage, basically being the OSX equivalent to the Windows registry. User Defaults are the way how you can persist small amounts of data in a convenient way. They are basically dictionaries that the system takes care of for you with the added benefit of being cached in memory.

Today we’ll up it one notch. Session 124 of the WWDC 2010 videos brought to my attention the fact that there’s also a mechanism to provide default values for the defaults. Up until now I would have retrieved an object from the defaults, checked if it’s nil and then set the value. Consider the following code snipped from SpeakerClock:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSNumber *countdownNum = [defaults objectForKey:@"Countdown"];
 
if (countdownNum)
{
	countdown = [countdownNum doubleValue];
}
else
{
	countdown = self.currentPreset.startDuration;
}

This works, but it’s not elegant. Wouldn’t it be great if we could pre-register those values so that a simple retrieval always has a result?

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UPDATE: Added handleOpenURL to the flow charts. Added UIApplicationExitsOnSuspend. Untangled some lines.

UPDATE: renamed deprecated handleOpenURL to newer name.

Now that we all are moving our source code gradually to iOS 4 I had to pause and think a bit about where to move which code. A problem that I’m facing frequently when updating a project is that the didFinishLaunching is only called if the app really launches.

That poses a bit of a challenge if you are used to doing things like refreshing images or other files off the internet. An app that is resumed from standby does no longer go through this delegate method. So an app that would always show fresh content upon launch before 4.0 multitasking would no longer load any new content as soon as you build it for 4.0. That’s actually one of the main reasons why I have not yet had time to update MyAppSales to 4.0.

To gain the possibility for “fast app switching” you actually don’t need to do anything. All apps automatically support it because they no longer get terminated if the user pushes the Home button. They get put into a sleep mode while the iPhone still has enough memory for everything else. It’s only if RAM runs out that the OS starts killing apps. There is begins with the ones that have the most memory reserved.

I grabbed the free trial of Omnigraffle and the Non-techie Process Flowchart Stencils by gfraser. Then I researched when all these various delegate methods of UIApplication are being called and drew charts to illustrate the flow.

By inhaling first how it was before multitasking and then upgrading your mental process to backgrounding we can begin to fully appreciate how it all fits together.

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Prior to iOS 3.2 your only option for playing videos on iPhone was to use MPMoviePlayerController and only in full screen mode. It made sense because who really wants to look at stamp sized videos on his mobile phone.

The iPad changed all that and brought along several changes in how you can place videos. All those changes also made it into the iPhone SDKs. Here’s a pitfall that you might not have seen if you didn’t upgrade the SDK on one of your iPhone projects.
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As of SDK 3.2 most of the touch handling code in stock controls has been taken out and replaced with this amazing new technology called Gesture Recognizers. This means besides of using them yourself and creating your own you can also fiddle with behaviors of standard controls if they interfere with your own gestures.

I’m currently working quite a bit on something based on UIScrollView and there I found several things that I needed to tweak.

Disabling Pinch

The first modification I did was to get around a bug in UIScrollView.  I did not actually want user zooming in my scroll view, but just use the setting of the zoomLevel to scale images without having to redraw them. And you can only set the zoomLevel to values between min and max.

So, during autorotation, I reduced the min zoom scale, set the new zoom level and then set min and max both to the new zoom. But the problem with this, as of SDK 3.2., is that if you change the min or max zoomLevel property the scroll silently adds a UIPinchGestureRecognizer to itself via the addGestureRecognizer method that now all views have.
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