Neglected Potential

A common cause of problems in iOS applications can be memory warnings. In the simplest terms, when the device is running low on available memory, iOS issues a memory warning which tells all running applications to stop being so greedy and to free up any memory they don’t absolutely need (and if that doesn’t free up enough, it will just start ruthlessly slaughtering them one by one). If an application doesn’t handle this properly and does something like release an object from memory without unlinking it, you can get a crash. Often times this will arise when a user has drilled down several views deep, a memory warning occurs, and as the user navigates back up the stack… kaboom! Let’s say a user is in an application, which has a photo albums view, and from there the user selects an album, and in that album they select a photo. So we have something like: Photo Albums view > Album view > Photo view. Normally when you’d come back to something like the Photo Albums view, it would have a reference stored of which photo album you tapped on so that it could do a fancy deselect animation when you came back up out of your album view. So let’s say you’re on Photo Details, a memory warning gets issued and in an attempt to free up memory, the application releases the contents of the Photo Albums view, including the cell that you tapped and which it is holding a reference to. As you come back out of the stack to the Photo Albums view, the application will try to reference the cell for the album that you tapped, and be like “WTF? That cell doesn’t exist.” Naturally the application will throw a temper tantrum at this point, or in more technical terms, it will crash. This is just one type of scenario that can cause a crash from a memory warning. (I might cover more later, but for now it’s just important to know that nested views are where to look for these issues). Memory warnings, like all relationships, occur naturally in the wild all the time, but it’s so much easier if you can just force them to happen when it’s convenient for you. Fortunately for us, iOS Simulator provides this functionality. You can simulate a memory warning by going to the Hardware menu in iOS Simulator and selecting Simulate Memory Warning (who knows why they named it something so cryptic). You should go ahead and set a keyboard shortcut for this now because you’ll be using it a lot from now on. For this just go to System Preferences, then select the Keyboard preference pane. Then select the Keyboard Shortcuts tab, select Application Shortcuts in the left pane, then click + at the bottom. Set Application to iOS Simulator, Menu Title to Simulator Memory Warning and your shortcut to whatever you want (I went with ⌘-1 because I think memory warnings are A #1). Also remember as you’re finding these crashes to note the path you took through the views to make it happen; no need to give developers another reason to curse your name.