If you’re looking to get higher frame rates and general application performance tweaks from your iOS application, you may need to take a look at transparent settings on your subviews. Any time you set a subview to be transparent, the OS has to blend multiple layers together to figure out the end flattened result. This blending takes CPU cycles and can impact performance of your app – especially in something as simple as a UITableViewCell.
Luckily there is an easy way to find these problems using Xcode’s companion tool, Instruments.
One of the instrumenting tools you can use on an app deployed to a device is Core Animation. The Core Animation instrument has a bunch of fancy switches you can flip.
That will turn on a visual indicator to show where multiple transparent layers exist on the screen. For example, the main table view of my app MigraineDiary shows the following:
To get your app into Instruments, simply select the “Profile” menu item under “Product”. This will build your app and launch Instruments. Make sure you have your device selected and not the iOS Simulator. Any areas that are heavily colored in red should be reviewed by you to ensure you’re not setting layers transparent that don’t need to be. This includes using [UIColor clearColor]!
You’ll notice transparency indicators in red on system components like the tab bar and nav bar. There isn’t much you can do about these, so you can really just ignore them. If you’ve overridden behaviors, however, you may wish to review your code to make sure you’re not breaking something.