bundle

What is Bundle?
A bundle is a directory in file system that groups executable code and related resources such as executable code, images, sounds, nib files, private frameworks and libraries, plug-ins , loadable bundles.
event contain runtime-configuration file called the information property list(Info.plist)

feature
1.easy to install or relocate an application.
2. internationalization. you can setting English GUI and easy change to French GUI.
3.App can dynamically load code and resource from main bundle or subordinate bundles as require.

PS:
nib file
a special type of resource file use to store user interface of iOS and Mac Apps.
(like older storyboard)

Demo
use bundle switch storyboard in different Device
purpose:
iphone device use Main.storyboard automatically
ipad device use ipad.storyboard automatically

Detect method 1:
use userinterfaceIdiom to detect screen

add ipad.storyboard

use currentDevice to switch storyboard in different device

chose iphone device

show the main.storyboard automatically

show ipad.storyboard automatically

add PressMe code

add class ViewController in ipad.storyboard

drag Outlets to GUI connect code

drag Outlets to GUI connect code

now Press Me button will show ipad storyboard on Top

Detect method 2 :
use [[UIScreen mainScreen] bounds].size.height to check device

SourceCode

Data From
https://developer.apple.com/library/content/documentation/General/Conceptual/DevPedia-CocoaCore/Bundle.htmlhttp://blog.csdn.net/startexcel/article/details/7099234

Edit:
20171121: add bundle example code