objective c - iOS what is difference between Different type of app delegate? -

i beginner in ios , know basic question creates confusin many times me , faced several issue due app delegate declaration. difference between type of appdelegate declaration , when declared it?

1) when declared appdelegate object .

//in viewcontroller.h file  #import "appdelegate.h" #import "friendsviewcontroller.h" #import "xmppstream.h" @class appdelegate; @interface viewcontroller :uiviewcontroller<xmppstreamdelegate,uitextfielddelegate, uialertviewdelegate, uiapplicationdelegate>  {     uiview *padding;     appdelegate *appdelegate; } 

2) when declared appdelegate in properties.

//in viewcontroller.h file @property (weak, nonatomic) appdelegate *appdelegate; 

3) when declare appdelegate in viewcontroller.m file make object.

//in viewcontroller.m file uistoryboard *storyboard = [uistoryboard storyboardwithname:@"mainstoryboard" bundle:[nsbundle mainbundle]]; appdelegate *appdelegate = (appdelegate *)[[uiapplication sharedapplication] delegate]; 

4) when declare appdelegate this

// in viewcontroller.m file +(appdelegate *) sharedappdelegate {     return (appdelegate *) [uiapplication sharedapplication].delegate; } 

difference

- (appdelegate *)appdelegate {     return (appdelegate *)[[uiapplication sharedapplication] delegate]; } 

i know basic question many people me face difficulty declare.

first 1 used create private object of class.

appdelegate *appdelegate; 

second 1 used create public , global object of class, used property attributes.

@property (weak, nonatomic) appdelegate *appdelegate; 

but first 2 object declaration third, fourth , fifth same, differance dot(.) used getter , setter method, square brackets shows not property, instead class method of class.

in declared object passing instance of appdelegate

4th case class methods , 5th case instance method

appdelegate *appdelegate = (appdelegate *)[[uiapplication sharedapplication] delegate]; //or appdelegate *appdelegate = (appdelegate *) [uiapplication sharedapplication].delegate;