I am building an application in iOS8 and have had issues with the status bar with all native functions such as the mail composer, the camera, etc.. The following will solve your issues:
Put the following in your plist file
<key>UIStatusBarHidden</key>
<false/>
<key>UIViewControllerBasedStatusBarAppearance</key>
<false/>
If you are using the add row feature in storyboard, the UIViewControllerBasedStatusBarAppearance is not an option. Also when adding a row it asks for BOOLEAN (YES/NO). It cannot be a NO string in the source code it must be a false boolean. Open the plist as source code instead and add the above rows. Remove your old attempts. You will now be able to successfully apply the code snippets given in so many incomplete answers found on the net.
You can now add global changes in the app delegate file and/or overrides in the controllers themselves. Without the above being in place all the stack overflow code I have tried has failed when using a native function. Now all is working perfectly.
As a test, replace any calls to any onboard "completion" calls with
completion:^{[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];}