ios - Expected Type in Protocol -

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i implemented protocol in objective-c , when use own class type definition xcode tells type required.

#import <foundation/foundation.h> #import <uikit/uikit.h>  #import "lprphotocapturecamera.h"  @protocol lprphotocapturecameradelegate <nsobject>  - (void)camera:(lprphotocapturecamera *)camera finishedcapturingphoto:(uiimage *)captureduiimage;  @end

i looked in header files apples delegates , edited protocol @class lprphotocapturecamera , works.

#import <foundation/foundation.h> #import <uikit/uikit.h>  #import "lprphotocapturecamera.h"  @class lprphotocapturecamera; @protocol lprphotocapturecameradelegate <nsobject>  - (void)camera:(lprphotocapturecamera *)camera finishedcapturingphoto:(uiimage *)captureduiimage;  @end

i wonder why xcode not throw error uiimage here, have explanation this?

what happened (i guessing because did not show files) lprphotocapturecamera.h imports lprphotocapturecameradelegate.h @ top of file. have import cycle.

so example, when compiling lprphotocapturecamera.m, import lprphotocapturecamera.h, imports lprphotocapturecameradelegate.h @ top of file (before declaration of lprphotocapturecamera class). lprphotocapturecameradelegate.h imports lprphotocapturecamera.h, #import guarantees file imported once, import doesn't import anything. when gets inside declaration of lprphotocapturecameradelegate protocol, refers type lprphotocapturecamera *, doesn't understand because lprphotocapturecamera hasn't been declared yet.

in other words, although lprphotocapturecameradelegate.h imports lprphotocapturecamera.h, import doesn't import lprphotocapturecamera because have started importing (and in middle of) lprphotocapturecamera.h @ higher level.

the usual way deal when types refer each other in cycle use forward declarations. declaration of lprphotocapturecameradelegate uses pointer lprphotocapturecamera, doesn't need declaration of lprphotocapturecamera class -- needs know it's class. forward declaration @class lprphotocapturecamera do, allow no longer import lprphotocapturecamera.h in lprphotocapturecameradelegate.h. similarly, if declaration of lprphotocapturecamera uses lprphotocapturecameradelegate in type of variable, e.g. id<lprphotocapturecameradelegate> delegate, doesn't need declaration of lprphotocapturecameradelegate -- needs know it's protocol, forward declaration @protocol lprphotocapturecameradelegate do, , don't have import lprphotocapturecameradelegate.h in lprphotocapturecamera.h. usually, time need import b's header in a's header if implements b protocol or inherits b class.





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