Question

I have a navigation based application, I push uitableviews with “init with nib name”.

I tested the app with instruments there is no leaks and in All allocations menu I see live bytes around 2-3 MB. when I start navigation and go through 30 pages, in Instruments I can see from “live bytes” that it adds around 40 KB for each pushed uitableview, which I think normal.

Then I wanted to test it in my IOS4 phone and with a free activity monitor application that I have found in app store. Well, I can see that in each push the total free memory in device gets less around 800KB!

so after 30 pushes 28 MB of free memory is gone, and when I do “back” through navigation then I can see that memory gets freed again.

I can post some code if you want, but I couldnt find that what could take 800Kb memory in my uitableView, all allocs are released and I dont allocate any image file. I just send a few lines of information to be displayed in the table.

What is your suggestion? which parts should check in mycode? or is this normal and pushed views can take up to hundres KBs of memory. because if there are 100 pages in my app then it can grow up to 100 Mb of memory

Thanks

Answer 1

I am pretty sure that if you inspect memory in Instrument by using the “Memory Tool” (see picture), you will see about the same usage of memory as what you see by using the free iphone app.

Indeed, it is my experience that Instruments will give you different information about memory usage depending on the tool that you use; and, unfortunately, the Memory Tool is the one that gives the most “realistic” estimation. I cannot explain why, but it is no surprise to me that for a few MB of “live bytes” you have many more MBs of “real memory”.

Anyway, I would not worry about it. If you get to 28MB and the app is not killed, you are possibly using a “later” devices (not iPod touch, nor iPhone 3); I guess that if you tested on an older device, the overall memory occupation could be lower (i.e., your application would get more memory warnings and if everything is done correctly, more views would be unloaded freeing more memory).

What is important, IMO, is that when you go back, memory is recovered. Ideally, it should be entirely recovered, but this is not always easy to attain.

About the overall memory consumption of your app, my thinking is:

1. first of all, you should check what happens when your app gets a memory warning; I expect that many of your previously loaded views will be unloaded and memory recovered; you can override didReceiveMemoryWarning in your controller to log that they are unloaded (don’t forget to call super) and memory recovered when needed (the system will know when it does); as I said, I suppose that your app is filling up memory because it does not receive any memory warning, the point is what happens when a memory warning is received; if memory is recovered, then no problem; problem is when you receive a warning and memory does not decrease significantly;

2. if problem persists (i.e., the memory recovery mechanism does not work properly for you), you could consider popping the view controllers from the navigation controller before pushing the new ones. You can try if this works for you…