CODEWITHSUNDEEP
iosobjective-cmemorymemory-managementios7
knagode
knagode

Reputation: 6125

Memory management in IOS7 and "Terminated due to Memory Pressure"

The reason why I am doing everything below: I have a GPS tracking application which should run in background all day long. Memory usage doesn't go down when I put application in background. It seems like views are not removed from memory when app goes into the background... That is why the app is closed in few hours of normal usage of iPhone ... From IOS6 experience - memory usage should drop to cca 8KB.

Then I tried to debug/isolate the problem ...

I created simple ViewController with UIMapKitView just to make sure that view is consuming a lot of RAM (e.g.: 12-17MB). When app goes to background app uses same amount of RAM until "Terminated due to Memory Pressure" message. Still - sometimes memory lowers to 4KB and everything is OK. Problem is because it works kind of "random" and the app is plain simple.

Can I manually release RAM which is consumed by views? E.g.: set self.view = nil? Should I do it?

I also noticed that "- (void)didReceiveMemoryWarning" is not always called before app is killed. I would expect that when OS needs more memory it would first release views, than ask me to clear anything I can via this method ... Isn't this a little bit strange?

Upvotes: 0

Views: 368

Answers (2)

knagode
knagode

Reputation: 6125

In my case the problem was specific IOS7 version. Every app was crashing with this version of OS. When we updated OS version, everything started working back as it should.

Upvotes: 0

Duncan C
Duncan C

Reputation: 131426

Apple redesigned the way a VC's (view controller's) views were loaded quite a while back - I want to say starting with iOS 5? iOS 6? It used to be that the system would unload your VC's views when a VC was not front-most and it needed the memory.

With the changes, a VC's views are NEVER unloaded while the VC is active. ViewDidLoad only gets called once in the lifetime of the VC, and viewDidUnload is no longer called at all.

I don't know what would happen if you set your (non-frontmost) VCs' content views to view manually. Would the system load your view hierarchy when that view became frontmost again? You'd have to try it, but it is risky since I don't think the OS is designed that way any more.

If your VCs views are holding significant amounts of memory, you might want to re-architect your app so only the front-most app is kept around, and the other VCs are released (after saving their state.)

Apple does not make this sort of app easy to write. To the contrary, they actively discourage it. The GPS is a huge power drain, so keeping it active constantly is going to drain the user's battery fast.

I remember hearing about a new location chip in the 5s that will record a "crumb trail" of location data for your app even when it's not running, at your request. You might look into that, although it would only work on the newest devices with the A7 chip and location chip.

Upvotes: 1

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