Creating Frameworks for iOS/OS X App Development

Creating Swift Frameworks

Creating Swift Frameworks is easy. The steps below walk you through creating a Swift Framework. The steps below have been performed on Xcode 7.3

Launch Xcode.
Select Create New Project. Or from the menu bar select File > New > Project
From the Template chooser select the Framework & Library Option under iOS
Select Cocoa Touch Framework
Give your project a name.
Make sure the language selected is Swift.
Feel free to enter values of your choice for organisation name and organisation identifier.
Save your project. Optionally, if you have a version control repository like Git you may save it there.
In left hand side bar make sure you have selected the Project Navigator.
Within the Project Navigator make sure you have selected the folder named after your project.
Click on File > New > File.
Make sure iOS Source is selected on the left hand side.
Select the file type as Swift.
Write down the code that you want to make available through a framework.
Now this is the key point. Place the keyword public before all the elements that you want to make publicly accessible.Why do we need to do this? To understand this we need to understand the scope of different elements within a typical Swift project.
Different variables/classes/functions that are declared within a module are accessible freely within the module. Swift files contain code & are themselves found within Swift modules. So a module can mean project or a framework.So, to access the variables/functions/classes from module A in module B, we have to make those elements of module A public in order to access them in module B.

For more information, do read Apple’s Swift Documentation.
The next steps depend on what your ultimate objective is. If you wish to build a framework for distribution then you need to follow a process that is similar to distributing an app. You need to get the code signing done & prepare the project for distribution.
If however, you plan to release it internally, or even just test it. Then you can follow the steps below.
Firstly, our objective is to make this framework run on both OS X(macOS) as well as iOS.
To do that we will be adding a new target. Click on File > New > Target.
Select OS X & the Frameworks & Libraries from the sidebar.
Select Cocoa Touch Framework
Give your framework a unique name. Something that indicates this framework is for OS X(macOS).
Now, we don’t need to rewrite the code for the Mac. We can simply make the file we have written a member for the OS X Framework Target.
To do that make sure that the right hand side sidebar is visible.
In the left hand side sidebar make sure that you have selected the new Swift file with the code you have written in there.
In the right hand side sidebar select the Document Inspector.
Under Target Membership make sure that both the Targets are checked. The target for iOS should already be checked.
Thats it. If you do not wish to make your code available for both iOS & OS X then skip steps 19 – 27.
The next part is building the framework. We will be building this framework for use internally. We will first build the iOS framework.
From the tool bar, make sure the target selected is for iOS. For the device you can select any device that you wish.
Then click on Product > Build to build the framework. If all goes well then you should get the message Build Succeeded on your screen.
To get hold of the framework, expand the product folder from the left hand side sidebar.
Select the Framework you have just built. Note that it should be black in colour. If you have opted to make a framework for OS X, then you should see that framework listed too, it should be in red colour. The red colour indicates that it has not yet been built.
Control-click on the iOS version of the framework and select Show in Finder.
This will take you directly to the folder containing the framework. Copy paste it to the desktop or to any other location to easily access it when required.
Repeat steps 30 – 34 to build the OS X version of the Framework. Make sure that the target selected is OS X.
Once we have done that, we need to test the framework we just created.
Create a dummy iOS Project for testing.
From the left hand side project navigator make sure that the blue project settings file is selected.
Make sure that the Target is selected within the settings screen.
Under the General tab scroll down to the Embedded Binaries section.
Click on the ‘+’ sign to add a framework.
Click on Add other
Navigate to the folder where you saved the Framework and select it.
Click Open
Select Copy Items if needed
The framework should be added to your project.
In the ViewController.swift file import your Framework: import CustomStack
Replace CustomStack with your frameworks name.
Try to write the code which uses the elements you have packaged within the framework.

Creating Mixed Frameworks (Swift & Objective-C)

The process of creating a mixed library is straightforward. Its almost the same as above with some minor differences.

Follow the steps mentioned above to add your Swift Code.
Add your objective-C files to the project.
While adding the files make sure that the checkbox for the targets is selected appropriately.
Write the code that you wish to write in Objective-C. Of course, if you are including prewritten files then you do not need to do this.
To make the Objective-C code accessible in Swift you need to make the following changes:
1. In the umbrella header of your framework add the line to import the header
```
#import "<FrameworkName>/<HeaderName>.h
```
2. Modify the access property located within the target membership of the Objective-C header file.
This should make your Objective-C code accessible to the Swift files.
Test the changes by accessing your Objective-C code in your Swift files within the framework.
Test the changes further by embedding your mixed language framework into a project & then try to access both the Swift as well as Objective-C versions of the code in your new project.
To make your Swift code accessible to Objective-C File make the following changes:
1. Make sure that your Swift code is compatible with Objective-C. There are 2 ways of doing this. One you can make your Swift class inherit from NSObject. The second way is to use the @objc keyword before your class declaration.
2. In the Objective-C header file add the line to add the bridging header which is auto generated. You do not need to create your own bridging header.
```
#import "<FrameworkName>/<FrameworkName>-Swift.h"
```
  Replace the word FrameworkName with the name of your Framework.
3. This should allow you to access your Swift code in your Objective-C header file within the same Framework Project.
This way you can make a single framework which contains code written in both Swift & Objective-C.