Sometimes when compiling more sophisticated iOS projects you need the IOKit headers which were removed from the iOS SDK a few versions ago. A simple workaround is to copy them from the Mac OS SDK to the iOS SDK with these commands:
sudo cp -r /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/IOKit.framework/Versions/A/Headers /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks/IOKit.framework
Sometimes you also need OSTypes.h from libkern:
sudo cp /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/include/libkern/OSTypes.h /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/libkern
If you still have build errors check you are building for device and not simulator.
This post is about my Stack Overflow answer.
In Xcode, Window->Devices, choosing a device and clicking the up arrow in the bottom bar brings up the console and this traditionally allowed you to view output from your app when not running in the debugger, e.g. for testing background launching behaviour. Unfortunately as of Xcode 8 and iOS 10 there is now a lot more log output – very low level debug logging is on so hundreds of lines pass by every second, making it impossible to see the logs you are interested in.
The solution is to upgrade to macOS Sierra, the new Console app now displays connected devices, and it allows filtering the log by many different categories, process is probably the most handy where you can simply enter the name of your app’s executable. This now makes the Xcode Devices log redundant, it never was very good at search anyway.
Some of the new iOS 10 features contain link-time checks, that is they are only enabled if the app was linked to the iOS 10 SDK. When working on an open source library it is necessary to debug when linked to an older SDK, e.g. iOS 9.3, on a newer device iOS, e.g. iOS 10. It currently isn’t possible to deploy to a newer iOS device with the old Xcode designed for the older SDK. For this reason it can be necessary to enable the older SDK in the newer Xcode, which can be done as follows:
Note: these commands assume Xcode 7 is at \Applications\Xcode.app and Xcode 8 is at \Applications\Xcode-beta.app
sudo ln -s /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS9.3.sdk
sudo ln -s /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator9.3.sdk
sudo /usr/libexec/PlistBuddy -c "Set :MinimumSDKVersion 9.3" /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Info.plist
sudo /usr/libexec/PlistBuddy -c "Set :MinimumSDKVersion 9.3" /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Info.plist
After running these commands, restart Xcode 8. Now you can set the Base SDK to iOS 9.3 and deploy to an iOS 10 device.
Any newer code generation features in Xcode 8 will need to be turned off, e.g. a Core Data model will need to have code generation set to none.