https://developers.facebook.com/docs/ios/share/cn

https://github.com/fbsamples/ios-howtos

http://stackoverflow.com/questions/18459252/how-to-post-on-twitter-by-hiding-slcomposeviewcontroller-tweetsheettweet-instan/18460093#18460093

http://stackoverflow.com/questions/12503287/tutorial-for-slcomposeviewcontroller-sharing

http://stackoverflow.com/questions/9092142/ios-uialertview-button-to-go-to-setting-app