CODEWITHSUNDEEP
iosiphoneipadxcode-instruments
MLQ
MLQ

Reputation: 13511

App freezes but CPU usage increases over time

I've been stuck on this thing for many hours now and I don't know what else to search for.

There's not much I can provide since the debugger doesn't show any errors but it's reproducible--I tap on a very specific item in a table view, the act of which should dismiss that modal, and then my app freezes. That doesn't happen for the other items in the table view--the modal dismisses perfectly and the app goes on.

I checked this answer suspecting that it's a deadlock, however:

How can I debug this thing? I've been looking around Xcode Instruments but I can't make sense of the data I'm seeing. The System Trace template, specifically, seems capable of stopping right when the freeze occurs, unlike the others which keep on recording.

Added: What I see in System Trace What I see in System Trace

Upvotes: 1

Views: 1506

Answers (2)

MLQ
MLQ

Reputation: 13511

@Paulw11's comment helped--the Time Profiler template is better suited for this task than the System Trace instrument.

I used the Time Profiler and got led to a bunch of traces that point to the UINavigationBar as the suspect repetitive caller to my custom UIControl's layoutSubviews. To further explain my view hierarchy:

  • My "Home" view controller has a custom title view in its UINavigationItem
  • The custom title view is a custom UIControl that launches a modal when tapped

Here's the deal: If I alloc-initWithFrame my custom UIControl with a frame of CGRectZero, the app freezes. If I provide a garbage initial value to the frame (which is disregarded anyway since UINavigationBar reshapes my custom UIControl) like CGRectMake(0, 0, 10, 10), the crash doesn't happen.

I'm guessing that UINavigationBar gets confused about how to layout a custom title view that has an initial frame of (0, 0, 0, 0). Sounds like an Apple bug.

Note: I'm running on iOS 8.2.

Upvotes: 0

nmock
nmock

Reputation: 1907

Instruments is the tool you want to diagnose the issue. Try inspecting your app with Time Profiler, performing the task that you were observing to increase CPU usage and then analyze the results, checking Invert Call Tree and Hide System Libraries. You can also set time markers if there is a specific time period you are looking to inspect. From here, you can see what calls are sucking up the CPU.

Upvotes: 2

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