objective c - what is the meaning of + symbol in iOS file naming? -

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i have seen examples of ios project, little confused naming rule of file. meaning of + symbol in ios naming rule? in case should use symbol.

and mean put draggle within ().

hopefully can help. thank much.

those categories

see here: https://developer.apple.com/library/ios/documentation/cocoa/conceptual/programmingwithobjectivec/customizingexistingclasses/customizingexistingclasses.html

the "draggable" category of uicollectionview

here's snippent apple:

if need add method existing class, perhaps add functionality make easier in own application, easiest way use category.

the syntax declare category uses @interface keyword, standard objective-c class description, not indicate inheritance subclass. instead, specifies name of category in parentheses, this:

@interface classname (categoryname)    @end 

here's example

#import "uiview+roundify.h"   @implementation uiview (roundify)  -(void)addroundedcorners:(uirectcorner)corners withradii:(cgsize)radii {     calayer *tmasklayer = [self maskforroundedcorners:corners withradii:radii];     [[self layer] setmask:tmasklayer]; }  -(calayer*)maskforroundedcorners:(uirectcorner)corners withradii:(cgsize)radii {     cashapelayer *masklayer = [cashapelayer layer];     masklayer.frame = self.bounds;      uibezierpath *roundedpath = [uibezierpath bezierpathwithroundedrect:                                  masklayer.bounds byroundingcorners:corners cornerradii:radii];     masklayer.fillcolor = [[uicolor whitecolor] cgcolor];     masklayer.backgroundcolor = [[uicolor whitecolor] cgcolor];     masklayer.path = [roundedpath cgpath];      return masklayer; }  @end 

header

@interface uiview (roundify)  -(void)addroundedcorners:(uirectcorner)corners withradii:(cgsize)radii; -(calayer*)maskforroundedcorners:(uirectcorner)corners withradii:(cgsize)radii;  @end 

this means when import file, can call method "addroundcorners" uiview