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We're discussing interoperability in the Swift programming language.

So it's going to be pretty common that you have some legacy Objective-C code and

you want to be able to use that in your new Swift code.

Or you might have new Swift code and you want to be able to use that in a legacy

Objective-C area, so we're going to talk about that.

We're mainly going to talk about the mechanics of getting your project to

a point that will allow that.

There's some other aspects of when you use Objective-C and Swift,

how you would use blocks as closures and we'll leave that up to you to look up.

But this is mainly going to talk about how we deal with the project, and

how we set up header files to import the right code into our Swift or

into our Objective-C files.

So if you're going from Objective-C to Swift, you need a bridging header.

And this is automatically created for you by Xcode,

if you already have an Objective-C project and

you bring in a Swift file, so we'll see that in just a little bit here.

But if you're going to do it manually,

then you need to name the file a certain way.

So, you can see here it has to be named [ProductName]-Bridging-Header.h.

And there you would bring in your, you would actually write whatever Objective-C

files that you have, header files that you want to bring into Swift.

And then you can just write from the Swift code,

start accessing that Objective-C code.

And a note that the product name, it is product name not target name.

And for the most cases, if you look at an Xcode project, the target name and

the product name are the same, but they can be different, so

just to note that the, it's the product name not the target name.

And then in the Build Settings area, there is actually a Objective-C bridging

header area that you need to actually put the name of this bridging header into.

Again, that's usually done automatically for you but if you do it manually

then you have to find that and put it in the name of your bridging header in there.

And once you do that and

you are going to access your Objective-C code in your Swift file,

all of your code from your Objective-C is fully compatible there in Swift.

Now, if you're going from Swift to Objective-C, you need to,

in your Objective-C file where you're going to access your Swift code,

you need to put in an import statement.

You don't have to create, this is an auto-created file.

So you're not creating a file in this case,

you're actually just importing this name.

So you'd have your [ProductName]-Swift.h and

that would be in your Objective-C file somewhere.

And again, product name not target.

And your Swift classes that you're going to bring into Objective-C,

they have to inherit from an Objective-C class, so like NSObject, for instance.

And we'll see that in just a little bit here, when we look at the Xcode project.

Any Swift declarations marked as private will not be imported.

And not all Swift features are compatible, so

it's not like going from Objective-C into Swift.

There are some newer features in Swift that Objective-C just

won't be able to understand and be compatible with, so generics, for example.

And there's a list of them and if you want to see that list, look for,

using Swift from Objective-C, and that's in the iOS developer library.

So let's go ahead and look at our Xcode project now.

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Interoperability Part 1

Toward the Future of iOS Development with Swift

Meet the Instructors