In Swift, I extend the class "Date" to add one method named "swiftDate" used to print it self. May I use the method "swiftDate" like [dateObject swiftDate] in Objective-C environment？
You need to import ProjectName-Swift.h in Bridging header file then you can access swift method in your objective c class.
Yes, ofcourse you can use it but you need to import NSDate_SwiftDate.h into bridging file ProjectName-Bridging-Header.h and also import ProjectName-Swift.h which is automatically generated when you create .h and .m file into swift project.
Yes, You can do it.
Just Import swift class and initialise instance of swift class.
and call your method like
[swiftInstance swiftInstanceMethod];
Today, I look up the Apple Developer Reference and find that the Date is a Class declared in Swift, instead of Objective-C. So, I can not only use it in Objective-C, not to mention using the extended methods in Swift.
Maybe, I should extend its ReferenceType----NSDate. The classes that conform the protocol ReferenceConvertible have a typealias ReferenceType. For Date, its ReferenceType is NSDate.
You can look up the link to learn more about ReferenceConvertible.
Related
I read this documentation for importing swift code into objective c.
https://developer.apple.com/documentation/swift/imported_c_and_objective-c_apis/importing_swift_into_objective-c
I have a few questions.
Can I put #objc annotation for a Struct?
Do I need to inherit all the class that I want to export to obj to be child of NSobject ? I am getting error 'error: only classes that inherit from NSObject can be declared #objc'
When I export a swift class with #objc, I need to add #objc to all its parent classes, protocol and interface and also class and structure in all its methods, is that correct?
No. Objective-C cannot see a native Swift struct.
Yes. Objective-C classes must basically be derived from NSObject. Objective-C can be made aware of the existence of other classes, but it cannot do anything useful with them.
You can mark the class with #objcMembers, in which case you will give everything within it full visibility to Objective-C.
I am running project with lots of legacy code with objc and swift.
I've been using objc MPOldKeychainManager, which is now deprecated and swift's NewKeychainManager is to be used.
The problem is following: MPOldKeychainManager had some categories written and I don't want to rewrite them as swift extensions.
What I've done is:
naming the class derived from the NewKeychainManager (visible in "myTarget-Swift.h") to "MPOldKeychainManager"
removing the objc declaration of MPOldKeychainManager
...hoping that the categories will still work.
objc(MPOldKeychainManager)
class NewKeychainManager: KeychainManager {
}
Unfortunately, old extensions can't see the MPOldKeychainManager (derived from swift), even though I've updated the imported header to myTarget-Swift.h
#import "myTarget-Swift.h" //previously - objc "MPOldKeychainManager.h"
#interface MPOldKeychainManager (Authentication)
Question: is it possible to use categories for objc classes derived from swift?
I have already tried totally new naming
I have already tried loads of clean-builds
In case you haven't seen it, here is a useful resource for migrating from Objective-C to Swift: https://developer.apple.com/documentation/swift/migrating_your_objective_c_code_to_swift . Among other things, it states that one cannot subclass a Swift class in Objective-C. What you are trying to do is specify a different Objective-C name, MPOldKeychainManager, for the NewKeychainManager Swift class.
This will, actually, work if you add an ampersand before objc, like so:
#objc(MPOldKeychainManager)
class NewKeychainManager: KeychainManager {
}
You can then use all your existing categories in Objective-C. You will, however, have a problem using them in Swift, because to be usable in Swift they need to be available in the bridging header, and you won't be able to use the class' Objective-C name (MPOldKeychainManager) in the bridging header.
You can, however, write an Objective-C wrapper class that will have a method corresponding to each category method and also taking a NewKeychainManager pointer. A wrapper method can then delegate to the category method, which is available to Objective-C code, so you won't have to re-implement your category methods in Swift.
Let's say an Objective-C category has method authenticateUser::
#interface MPOldKeychainManager (Authentication)
-(void)authenticateUser:(int32_t)uid;
#end
The method could be wrapped as follows:
#interface OldKCMWrapper : NSObject
+(void)authenticateUser:(int32_t)uid withManager:(NewKeychainManager*)inst;
#end
This interface declaration must be available, directly or indirectly, via the bridging header. Then, somewhere in your Objective-C code, the wrapper could be implemented thus:
#implementation OldKCMWrapper
+(void)authenticateUser:(int32_t)uid withManager:(MPOldKeychainManager*)inst {
[inst authenticateUser:uid];
}
#end
The wrapper can then be used in Swift code, e.g.:
let kcm = NewKeychainManager()
OldKCMWrapper.authenticateUser(321, with: kcm)
In fact, the wrapper could be used in a Swift extension of NewKeychainManager. You would still have a Swift extension with equivalents of all the Objective-C category methods, but you would not have to re-implement their code in Swift: methods in the extension would simply delegate to the wrapper.
Hopefully this is helpful. There are other ways of implementing this idea, possibly more elegant.
I'm trying to use my Swift class into Objective-C code and I came across this answer to do so. However, after import MyModule-Swift.h, I'm getting compile error in MyModule-Swift.h:
No type or protocol named 'AVCapturePhotoCaptureDelegate'
Even though it contains #import AVFoundation; at the top. I'm clueless how to solve this. All I'm trying to do is to use one of the model class (written in Swift) in Objective-C.
I think you are using .mm file.
Use .m instead.
I want to extend my class which I wrote in Swift. I want to write the extension in Objective C because I need to put some Objective C code which I can't port into Swift. I know that I can create a .h and .m and then include the .h at the bridging header. But in the .h, I need to include the original .swift class file right?
How can I solve this? Can I include using myclass-swift.h? Thanks.
The following documentation may be helpful: https://developer.apple.com/library/content/documentation/Swift/Conceptual/BuildingCocoaApps/MixandMatch.html#//apple_ref/doc/uid/TP40014216-CH10-ID122. You've probably already looked at that, but just in case. The following question may also help: Extending a Swift class with Objective C category.
As you know, to use Objective-C code in Swift there is the bridging header. To go the other way around, there is the auto-generated *-Swift.h header that should be imported in .m (and .mm) implementation files. The documentation says it should not be imported into .h files. In fact, the compiler won't let you import it into a .h file that is included, directly or indirectly, in the bridging header. However, with some care you can import it into other .h files.
Now, suppose your Swift class is called SwiftClass and you want to add to it a method called ocFunction() implemented in Objective-C. One approach, essentially presented in the aforementioned answer, is to implement a category in an Objective-C source file (.m):
#implementation SwiftClass (OCExtension)
-(void)ocFunction {...}
#end
Then modify your SwiftClass to include the following:
class SwiftClass : NSObject
{
...
#nonobjc func ocFunction()
{
self.perform(Selector(("ocFunction")))
}
...
}
The referenced answer suggests doing this in an extension, but since you have full control of the SwiftClass source, you can just do it in the class directly. BTW, the Objective-C category function could be named something other than the SwiftClass's function, thus eliminating the need for #nonobjc.
Another approach might be to define an Objective-C wrapper interface like this:
#interface SwiftClassOC : NSObject
+(void)ocFunction:(SwiftClass*)sc;
#end
and make it available to Swift via the bridging header. The implementation would go into a .m file. Then your ocFunction() in SwiftClass would look like
func ocFunction()
{
SwiftClassOC.ocFunction(self)
}
Please note that SwiftClassOC is stateless, so it's essentially a set of helper functions that take a SwiftClass pointer. SwiftClass is the one maintaining the state.
You can extend an Objective-C class with Swift, but you cannot extend a Swift class with Objective-C.
I want to write the extension in Objective C because I need to put some Objective C code which I can't port into Swift
You can do that, but not as part of the Swift class. What I usually do is make a "helper" class in Objective-C and import it into Swift.
Here is the code that I want to call in Swift:
+ (Client*) clientWithInfo:(ServerInfo*)info {
return [[[Client alloc] initWithInfo:info] autorelease];
}
Here is how I am calling it in Swift:
Client.clientWithInfo(ServerInfo)
But it gives me the following error:
clientWithInfo unavailable: use object construction Client(info:)
First you need to have bridging headers and in this file included name of your class.
#import "MySingletonClass.h"
After you should be able to call MySingleton.sharedInstance.methodName
Start by reading Apple's guide Using Swift with Objective-C (Swift 2.1). There's a section on importing Objective-C into Swift.
You need to create a Objective-C bridging header file. When you add a Swift file to an Objective-C project or an Objective-C file to a Swift project Xcode will ask you if you want to add an Objective-C bridging header?
To use your Objective-C code with your Swift code you would import every Objective-C header you want to expose to swift. Note that this is for the same target.
#import "MyCustomObjectiveCCodeWithSingleton.h"
From the documentation:
Any public Objective-C headers listed in this bridging header file
will be visible to Swift. The Objective-C functionality will be
available in any Swift file within that target automatically, without
any import statements. Use your custom Objective-C code with the same
Swift syntax you use with system classes.