Cannot find protocol definition for XXX

Question

I have declared a protocol firstly, and then use it. But I get a warning "Cannot find protocol definition for LeveyPopListViewDelegate". Here is the code:

@protocol LeveyPopListViewDelegate; @interface LeveyPopListView : UIView <LeveyPopListViewDelegate,UITableViewDataSource, UITableViewDelegate,UITextFieldDelegate> //the content of LeveyPopListView @end @protocol LeveyPopListViewDelegate <NSObject> //the definition for LeveyPopListViewDelegate @end

if I put the definition LeveyPopListViewDelegate at first, I can not use the LeveyPopListView in the protocol.

Max_: While some things we used to do with delegates are now better done with blocks, there are LOTS of reasons to use protocols. — Mark Bernstein
– Mark Bernstein, Commented Feb 21, 2013 at 2:04
not that it matters... your code is running fine without errors for me (XCode4.6) - I just tried it in some older versions in case something had changed, but it's ok also in 4.2 ;-j — foundry
– foundry, Commented Feb 21, 2013 at 2:36
But the weird thing is that despite the warning it does work, right? — Alper
– Alper, Commented Mar 16, 2018 at 11:20

DawnSong · Accepted Answer · 2018-11-03 08:03:23Z

I ended up suppressing all warnings for that particular line, which is not ideal but works well.

// Forward-declare protocols (to avoid circular inclusion) @protocol YourProtocol; #pragma clang diagnostic push // To get rid of 'No protocol definition found' warnings which are not accurate #pragma clang diagnostic ignored "-Weverything" @interface YourClass: NSObject // <YourProtocol> #pragma clang diagnostic pop

Make sure you do push & pop, otherwise you'll end up with all warnings being ignored for this file!

That did the trick. As I am using a Swift protocol, that was the only way to remove this warning. I also found a good source here in this blogpost from NSHipster

rmaddy · Accepted Answer · 2013-02-21 01:57:08Z

2

I always do it this way:

@class LeveyPopListView; @protocol LeveyPopListViewDelegate <NSObject> //the definition for LeveyPopListViewDelegate @end @interface LeveyPopListView : UIView <LeveyPopListViewDelegate,UITableViewDataSource, UITableViewDelegate,UITextFieldDelegate> //the content of LeveyPopListView @end

answered Feb 21, 2013 at 1:57

rmaddy

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4 Comments

Bohan Gao Over a year ago

But I want to use LeveyPopListView in protocol LeveyPopListViewDelegate

rmaddy Over a year ago

You can with what I posted. That's the point of the forward class declaration.

Bohan Gao Over a year ago

Thank you very much. But why declaring a protocol first will get a warning?

rmaddy Over a year ago

I've never been able to make forward protocol definitions work so I always do as I posted.

Ryan · Accepted Answer · 2013-10-08 16:39:29Z

If you followed the good advice in this post and still have the issue try just doing a clean. I was scratching my head over it for a while and a clean resolved the issue.

Denis Kutlubaev · Accepted Answer · 2018-12-06 18:31:57Z

1

This happened to me when I imported Swift protocol to Objective C class. What helped me is to add *-Swift.h file to the Objective C class file:

#import "MyApp-Swift.h"

and declare protocol as @objc:

@objc protocol VerificationGate

answered Dec 6, 2018 at 18:31

Denis Kutlubaev

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1 Comment

p13n Over a year ago

I am curious how that worked out. I have the same warning. It is not possible to import the automatically generated Swift bridging header in Objective-C headers as it is not generated yet. It can only be imported in Objective-C implementation files. But the protocol conformance is defined in Objective-C headers. A forward declaration in the Objective-C header does not help.

efimovdk · Accepted Answer · 2018-12-20 08:54:40Z

Also, if you declared and defined protocol in different file, you have to #import that file, forward declaration won't help in this situation.

BTW. Never suppress warnings as some answers suggest.

Victor Jalencas · Accepted Answer · 2015-06-05 13:50:07Z

It's unusual having to use a concrete class name in a protocol definition. What you should do (most of the cases, exceptions may apply… though they are a bad smell) is make your class conform to a protocol, and use that class in the delegate protocol definition.

It is also a bad smell that a class needs to be its own delegate. I'd revise the design carefully.

nkongara · Accepted Answer · 2013-02-21 01:58:52Z

You have to define the protocol first. Try like below

@protocol LeveyPopListViewDelegate <NSObject> //the definition for LeveyPopListViewDelegate @end @interface LeveyPopListView : UIView <LeveyPopListViewDelegate,UITableViewDataSource, UITableViewDelegate,UITextFieldDelegate> //the content of LeveyPopListView @end

But I want to use LeveyPopListView in protocol LeveyPopListViewDelegate
You can forward declare LeveyPopListView above the protocol definition. i.e @class LeveyPopListView;

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