iPad performance issues

I have this problem with performance of my iPad app..

For developing, I use MonoDevelop, which takes care of Garbage collecting. Still my questions are rather generic, I'd say.

OK, I use TabBarController with 5 NavigationControllers. Inside nav controllers there ar开发者_StackOverflowe some controllers, whose views are TableViews or ScrollViews. Next child is always just regular view.

I have a few questions:

1) TableViews never scroll smoothly. I have some alpha transparency, but since I did my graphics in Photoshop and not programmatically, this transparency should not cause much problems. It doesn't matter whether I have few or many results in table. On the other hand, I have ScrollView which serves same purpose, i.e. to be a table with different layout and buttons have Photoshop generated transparency as well. It works perfectly.

For tables I applied DequeueReusableCell() which works fine (I see that memory usage is not increasing after scrolling). So why would tables scroll so jerky?

2) My app supports rotation. When I scroll table or scrollView and simultaneously tilt the device a bit, I get maybe 1 or 2 FPS. What is the best way to implement rotation? As I understand, ShouldAutorotateToInterfaceOrientation has to be overridden in all controllers in NavigationController chain. Also, I need to add observer in View I want some changes to happen. Do I have to use BeginGeneratingDeviceOrientationNotifications() in all views or is it enough to do it in Main.cs? Maybe this slows it down?

3) After some time app starts getting memory warnings and then crashes eventually. I tried to read logs and run app with Instruments, but can't find the cause of crash.

4) What exactly happens to a View popped from NavigationController stack? I can't reuse it. But could it be that Monotouch (or me) doesn't dispose it correctly?

I have almost same app for iPhone without support for rotation which never crashes. I think I'm doing something wrong with this rotation, but I'm not sure what.

Any help will be appreciated the most. So, thank you in advance.

Regards

1 - transparencies are always a problem. Even if you're not rendering the images in code, the phone still needs to do the compositing of the image, and that may take a lot of time. UITableViews have to calculate the final composite image every time a new cell is displayed, or the table is scrolled, while UIScrollViews can calculate only once, since the image won't change. So be very careful about it, turn the transparency off, and check if performance improves.

2 - You shouldn't need to notify every uiview in your application. Receive the notification in the controllers that you want to update only, like for example if you want to rearrange items in the UIViewControllers view.

3 - you have one (or many) memory leaks. My guess is that MonoTouch probably can't garbage collect UIViews or UIViewControllers, because they're still being linked from somewhere in UIKit, like a UINavigationController

4 - UIViews are not disposed by UIKit until the app gets a memory warning notification.

Like Eduardo said, alpha transparency in Views comes at a price. There are some tools that you can use to identify the bottlenecks discussed in these WWDC 2011 talks from:

https://developer.apple.com/videos/wwdc/2011/

• iOS Performance and Power Optimization with Instruments
• Understanding UIKit Rendering

In the "Debug" menu of the iOS simulator you can find various debugging tools that will color different regions of the screen indicating where some problematic rendering is taking place. The WWDC 2011 talks show what you can do to fix those problems.

For your memory problems, it is very likely that you have something pointing out to your objects around, so you need to make sure those objects are gone. While we currently are not shipping our new profiler for MonoTouch that can show the source of the problem, I wrote a "poor man's" debug utility that will help you narrow down which objects are alive. It is available here:

http://tirania.org/tmp/HttpDebug.cs

Call HttpDebug.Start () from your application and as you run, connect with a web browser to http://localhost:5000 to get a list of live Objective-C objects surfaced to C#. The tool is not perfect and shows a lot of irrelevant data, but it would at least give you an idea of what is going on.