how to create and install own keyboard (like emoji) which we can use in any application?

emoji keyboard is being enabled on device when we enable the key KeyboardEmojiEverywhere in the plist file /private/var/mobile/Library/Preferences/com.apple.Preferences.plist

So,just with a key how can we get a keyboard? What is logic behind that?

I want to create my custom keyboard like emoji and want to install it on iphone,so that i can use it with any application with pressing globe button.

Please help. Thanks in advance.

With iOS 8, Apple has made it possible to create custom keyboard that user can access throughout the device(in other applications also). Please check Keyboard Extension.

You can create your own custom keyboard using Keyboard extension. You can check a nice tutorial here.