CODEWITHSUNDEEP
iosobjective-cswift
Andrew Paul Simmons
Andrew Paul Simmons

Reputation: 4513

Is it a possible for an objective-c class to implement a swift protocol in the .h

Is it a possible for an Objective-C class to implement a Swift protocol in the .h so that other Swift classes can reference the Objective-C class by the Swift protocol type?

Let MySwiftProtocol be the Swift protocol type, now assume I have this in .h for my class:

@protocol MySwiftProtocol;
@interface MyObj : NSObject< MySwiftProtocol>

Then I'll get a warning: cannot find protocol definition for MySwiftProtocol
The warning is no good, so that doesn't work.

So let's assume I do this in the .m and remove the references to the protocol in the .h.

@interface MyObj () <MySwiftProtocol>

Then I end up not being able to cast objects of type MyObj to type MySwiftProtocol in Swift classes.

So neither approach above works.

Please help!

Upvotes: 2

Views: 1099

Answers (1)

Andrew Paul Simmons
Andrew Paul Simmons

Reputation: 4513

According to apple. Forward declarations of Swift classes and protocols can only be used as types for method and property declarations. Further apple says, An Objective-C class can adopt a Swift protocol in its implementation (.m) file by importing the Xcode generated header for Swift code...

Basically you cannot mark an obj-c class as conforming to a swift protocol in the .h. So you must do it in the .m and then have the class pass itself to any object that is expecting a reference the objc object as the swift protocol type.

See sections Referencing a Swift Class or Protocol in an Objective-C Header and Adopting a Swift Protocol in an Objective-C Implementation at https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/MixandMatch.html

Upvotes: 2

Related Questions