Notarize a Command Line Tool

The upcoming macOS 10.15 Catalina will require more apps and tools to be notarized. Apple has some loosened the requirements at last minute, but these changed limitations are only temporary, to give developers more time to adapt.

Notarizing Mac Application bundles has its pitfalls, but is overall fairly well documented. However, I have been working on some command line tools written in Swift 5 and figured out how to get those properly signed and notarized.

Howard Oakley has written up his experiences and that post was extremely helpful. But there were a few omissions and some steps that aren’t really necessary, so I decided to make my own write-up.

And yes, there is a script at the end…

Note: these instructions are for macOS 10.14.6 Mojave, Xcode 10.3 and Swift 5.0. It is very likely that the details will change over time.

Update 2019-09-24: Tested with Xcode 11 and it still works (the screen layout has changed for some of the options)

What do you need?

  • Apple Developer Account (Personal or Enterprise, the free account does not provide the right certificates)
  • Xcode 10.3 or 11
  • Developer ID Certificates (Application and Install)
  • Application Specific Password for your Developer account
  • a Command Line Tool Project that you want to sign and notarize

That’s a longish list. If you are already building command line tools in Xcode, you should have most of these covered already. We will walk through the list step-by-step:

Apple Developer Program Account

You need either the paid membership in the Apple Developer Program or be invited to an Apple Developer Enterprise Program team with access to the proper certificates.

You cannot get the required certificates with a free Apple Developer account, unless you are member of a team that provides access.

Xcode

You can download Xcode from the Mac App Store or the developer download page. When you launch Xcode for the first time, it will prompt for some extra installations. Those are necessary for everything to in the article to work.

Developer ID Certificates

There are multiple certificates you can get from the Developer Program. By default you get a ‘Mac Developer’ certificate, which you can use for building and testing your own app locally.

To distribute binaries (apps and command line tools) outside of the App Store, you need a ‘Developer ID Application’ certificate. To sign installer packages for distribution outside of the Mac App Store, you need a ‘Developer ID Installer’ certificate.

We will need both types of Developer ID certificates, the first to sign the command line tool and the second to sign and notarize the installer package.

If you have not created these yet, you can do so in Xcode or in the Developer Portal. If you already have the certificates but on a different Mac, you need to export them and re-import them on the new Mac. Creating new certificates might invalidate the existing certificates! So beware.

Once you have created or imported the certificates on your work machine, you can verify their presence in the Terminal with:

% security find-identity -p basic -v

This command will list all available certificates on this Mac. Check that you can see the ‘Developer ID Application’ and ‘Developer ID Installer’ certificates. If you are a member of multiple teams, you may see multiple certificates for each team.

You can later identify the certificates (or ‘identities’) by the long hex number or by the descriptive name, e.g. "Developer ID Installer: Armin Briegel (ABCD123456)"

The ten character code at the end of the name is your Developer Team ID. Make a note of it. If you are a member of multiple developer teams, you can have multiple Developer ID certificates and the team ID will help you distinguish them.

Application Specific Password for your Developer Account

Apple requires Developer Accounts to be protected with two-factor authentication. To allow automated workflows which require authentication, you can create application specific passwords.

Create a new application specific password in Apple ID portal for your developer account.

You will only be shown the password when you create it. Immediately create a ‘New Password Item’ in your Keychain with the following fields:

  • Keychain Item Name: Developer-altool
  • Account Name: your developer account email
  • Password: the application-specific password you just created

This will create a developer specific password item that we can access safely from the tools.

If you want, you can also store the app specific password in a different password manager, but the Xcode tools have a special option to use Keychain.

A Command Line Tool Project

You may already have a project to create a command line in Xcode. If you don’t have one, or just want a new one to experiment, you can just create a new project in Xcode and choose the ‘Command Line Tool’ template from ‘macOS’ section in the picker. The template creates a simple “Hello, world” tool, which you can use to test the notarization process.

My sample project for this article will be named “hello.”

Preparing the Xcode Project

The default settings in the ‘Command Line Tool’ project are suitable for building and testing the tool on your Mac, but need some changes to create a distributable tool.

Choosing the proper signing certificates

Before you can notarize the command line tool, it needs to be signed with the correct certificates.

  1. in Xcode, select the blue project icon in the left sidebar
  2. select the black “terminal” icon with your project’s name under the “Targets” list entry
  3. make sure the ‘General’ tab is selected
  4. under ‘Signing’ disable ‘Automatically manage signing’
  5. under ‘Signing (Debug)’ choose your Team and choose ‘Developer ID Application’ as the certificate
  6. under ‘Signing (Release)’ choose your Team and choose ‘Developer ID Application’ as the certificate
Setting the certificates
Setting the certificates

Enable Hardened Runtime

Enabling the ‘Hardened Runtime’ will compile the binary in a way that makes it harder for external process to inject code. This will be requirement for successful notarization starting January 2020.

  1. from the view where you changed the signing options, click on ‘Build Settings’ in the upper tab row
  2. click on ‘All’ to show all available settings
  3. enter ‘enable hardened’ in the search field, this will show the ‘Enable Hardened Runtime’ setting
  4. set the value in the project column (blue icon) to YES
Enable Hardened Runtime
Enable Hardened Runtime

Change the Install Build Location

If we want to automate the packaging and notarization, we need to know where Xcode builds the binary. The default location is in some /tmp subdirectory and not very convenient. We will change the location for the final binary (the ‘product’) to the build subdirectory in the project folder:

  1. in the same view as above, enter ‘Installation Build’ in the search field, this will show the ‘Installation Build Products Location’ setting
  2. double click on the value in the Project column (blue icon), this will open a popup window
  3. change the value to $SRCROOT/build/pkgroot
Change the Installation Build location
Change the Installation Build location

If you manage your code in git or another VCS, you want to add the build subdirectory to the ignored locations (.gitignore)

Build the Binary

You can use Xcode to write, test, and command line tool debug your. When you are ready to build and notarize a pkg installer, do the following:

  1. open Terminal and change directory to the project folder
  2. % xcodebuild clean install

This will spew a lot of information out to the command line. You will see a build subdirectory appear in the project folder, which will be filled with some directories with intermediate data.

After a successful build you should see a pkgroot directory in the build folder, which contains your binary in the usr/local/bin sub-path.

/usr/local/bin is the default location for command line tools in the Command Line Tool project template. It suits me fine most of the time, but you can change it by modifying the ‘Installation Directory’ build setting in Xcode and re-building from the command line.

Build the pkg

Command Line Tools can be signed, but not directly notarized. You can however notarize a zip, dmg, or pkg file containing a Command Line Tool. Also, it is much easier for users and administrators to install your tool when it comes in a proper installation package.

We can use the pkgroot directory as our payload to build the installer package:

% pkgbuild --root build/pkgroot \
           --identifier "com.example.hello" \
           --version "1.0" \
           --install-location "/" \
           --sign "Developer ID Installer: Armin Briegel (ABCD123456)" \
           build/hello-1.0.pkg

I have broken the command into multiple lines for clarity, you can enter the command in one line without the end-of-line backslashes \. You want to replace the values for the identifier, version and signing certificate with your data.

This will build an installer package which would install your binary on the target system. You should inspect the pkg file with Pacifist or Suspicious Package and do a test install on a test system to verify everything works.

If you want to learn more about installer packages and pkgbuild read my book “Packaging for Apple Administrators.”

Notarizing the Installer Package

Xcode has a command line tool altool which you can use to upload your tool for notarization:

xcrun altool --notarize-app \
             --primary-bundle-id "com.example.com" \
             --username "username@example.com" \
             --password "@keychain:Developer-altool" \
             --asc-provider "ABCD123456" \
             --file "build/hello-1.0.pkg"

The username is your developer account email.

The asc-provider is your ten digit Team ID. If you are only a member in a single team you do not need to provide this.

The password uses a special @keychain: keyword that tells altool to get the app-specific password out of a keychain item named Developer-altool. (Remember we created that earlier?)

This will take a while. When the command has successfully uploaded the pkg to Apple’s Notarization Servers, it will return a RequestUUID. Your notarization request will be queued and eventually processed. You can check the status of your request with:

xcrun altool --notarization-info "Your-Request-UUID" \
             --username "username@example.com" \                                    
             --password "@keychain:Developer-altool"   

Apple will also send an email to your developer account when the process is complete. I my experience this rarely takes more than a minute or two. (Being in Central EU time zone might be an advantage there). When the process is complete, you can run the above notarization-info command to get some details. The info will include a link that contains even more information, which can be useful when your request is rejected.

Note that the info links expire after 24 hours or so. You should copy down any information you want to keep longer.

Completing the Process

You will not receive anything back from Apple other than the confirmation or rejection of your request. When a Mac downloads your installer package and verifies its notarization status it will reach out to Apple’s Notarization servers and they will confirm or reject the status.

If the Mac is offline at this time, or behind a proxy or firewall that blocks access to the Apple Servers, then it cannot verify whether your pkg file is notarized.

You can, however, ‘staple’ the notarization ticket to the pkg file, so the clients do not need to connect to the servers:

% xcrun stapler staple build/hello-1.0.pkg

You can also use stapler to verify the process went well:

% xcrun stapler validate build/hello-1.0.pkg

But since stapler depends on the developer tools to be installed, you should generally prefer spctl to check notarization:

% spctl --assess -vvv --type install build/hello-1.0.pkg

Automating the Process

Obviously, I built a script to automate all this. Put the following script in the root of the project folder, modify the variables at the start of the script (lines 20–38) with your information, and run it.

The script will build the tool, create a signed pkg, upload it for notarization, wait for the result, and then staple the pkg.

You can use this script as an external build tool target in Xcode. There are other ways to integrate scripts for automation in Xcode, but all of this is a new area for me and I am unsure which option is the best, and which I should recommend.

Links and Videos

These links and videos, especially Howard Oakley’s post and Tom Bridge’s PSU Presentation have been hugely helpful. Also thanks to co-worker Arnold for showing me this was even possible.

Going forward

Notarization is a key part of Apple’s security strategy going in macOS.

As MacAdmins we will usually deploy software through management systems, where the Gatekeeper mechanisms which evaluate notarization are bypassed. There are, however, already special cases (Kernel Extensions) where notarization is mandatory. It is likely that Apple will continue to tighten these requirements in the future. The macOS Mojave 10.14.5 update has shown that Apple may not even wait for major releases to increase the requirements.

If you are building your own tools and software for macOS and plan to distribute the software to other computers, you should start signing and notarizing.

On the other hand, I find the introduction of Notarization to macOS encouraging. If Apple wanted to turn macOS into a “App Store only system” like iOS, they would not have needed to build the notarization process and infrastructure. Instead, Apple seems to have embraced third-party-software from outside the App Store.

Notarization allows Apple to provide a security mechanism for software distributed through other means. It cannot be 100% effective, but when used correctly by Apple and the software developers it will provide a level of validation and trust for software downloaded from the internet.

Swift 5 for MacAdmins

macOS 10.14.4 also includes Swift 5. The main new feature of Swift 5 is that Swift is ABI stable.

Simply said, ABI stability allows swift binaries to use a Swift library on the system instead of having to bundle the libraries with them. This will, of course reduce the size of the binaries.

For example, my desktoppr tool compiles to 6.5MB with Swift 4.2 and 56KB with Swift 5.

However, command line tools built with Xcode 10.2 now rely on the Swift library to be available on the system. macOS 10.14.4 and future versions will include the libraries, but older macOS versions did not. There is no option in Xcode 10.2 to keep the old behavior of bundling the libraries in the tool.

This means that when you re-build a tool in Xcode 10.2 with Swift it will not run on older macOS version:

$ sw_vers -productVersion
10.13.6
$ ./desktoppr 
dyld: Library not loaded: @rpath/libswiftAppKit.dylib
  Referenced from: /Users/armin/Desktop/desktoppr
  Reason: image not found
Abort trap: 6

Apple provides an installer for the Swift libraries for “earlier versions of macOS.” (The package installer declares a minimum OS version of 10.9.)

The libraries are installed in /usr/lib/swift, where your binaries can find them:

$ ./desktoppr 
/Library/Desktop Pictures/BoringBlueDesktop.png

Note: these libraries are used by compiled binaries. Installing the runtime libriaries will not allow you to run swift script files, i.e. text files starting with the #!/usr/bin/swift shebang. You still need to install Xcode or the Developer Command Line tools for that.

So far, only command line tools written and compiled in Xcode 10.2 will require the libraries. Application bundles will continue to include their own libraries.

As Swift gets updated, you will need to update the installed libraries as well. You can get the installed version of the Runtime with pkgutil:

$ pkgutil --info com.apple.pkg.SwiftRuntimeForCommandLineTools
package-id: com.apple.pkg.SwiftRuntimeForCommandLineTools
version: 10.2.0.0.1.1552586384
volume: /
location: /
install-time: 1553789052
groups: com.apple.FindSystemFiles.pkg-group 

However, on a Mac with 10.14.4 the swift libraries are present but not installed by the same installer package, they are part of the entire system:

$ pkgutil --file-info /usr/lib/swift/libswiftFoundation.dylib
volume: /
path: /usr/lib/swift/libswiftFoundation.dylib

pkgid: com.apple.pkg.update.os.10.14.4.18E226
pkg-version: 1.0.0.0.1.1553145155
install-time: 1553765876
uid: 0
gid: 0
mode: 755

If/When Apple updates the runtime libraries, this might be a challenge to track and update properly.

Note: While I used my tool desktoppr as an example, I have not updated the version available for download to Swift 5 yet. So, that is still built with the “old” Swift and Xcode and should work everywhere without the runtime libraries.

Nevertheless, it should be prudent for MacAdmins to install the Swift 5 runtime libraries on their fleet. At the very least be aware that these errors can occur and how to fix them.

Build an Application to Run a Shell Command in Xcode and Swift – Part 2

At the end of the previous part you had a working application, but it did not do much. All user interaction consisted of a click on a single button. This part will add more functionality.

Note: please consider supporting the author of this site by purchasing one of my books! Thank you!

Add a Text Field

Right now the argument you are passing into the say command is fixed. It would be better to have a field where the user can enter arbitrary text that will be passed to the command.

In the file sidebar, select the ‘MainMenu.xib’ file and then move the ‘Talk’ button to the top right corner of the ‘SayThis’ window. As you move the button around the window blue lines will appear to guide you to the proper distances of the edges. Use these blue lines. Their alignments will help you later.

Use the blue guide lines to align the button in the top right corner
Use the blue guide lines to align the button in the top right corner

Next, use the object library in the lower right of the Xcode window to find a ‘Text Field’ object.

Object Library: search for text field
Object Library: search for text field

Drag the text field to your ‘SayThis’ window. Use the blue guide lines to align it in the top right corner and then extend it to the right until the blue lines show you it is right distance from the button.

Drag the right side until it snaps to the blue guide
Drag the right side until it snaps to the blue guide

You could now build the app and see the text field is there. You can even enter text. However, clicking the ‘Talk’ button will still only say “hello world” since you have not changed the code yet.

In your code you need to get the text from the text field. For that you need some reference to the text field object in the window. Create this ‘outlet’ the same way you hooked up the button action. First make sure you have a two part Xcode window. If you have closed the second pane, you can get it back by clicking the ‘Assistant Editor’ button in the top right window tool bar.

Just clicking this button shows or hides the second editor pane
Just clicking this button shows or hides the second editor pane

And then choosing the ‘AppController’ file for the second pane.

Choose the AppController file
Choose the AppController file

Then drag while holding the ctrl-key or with the secondary (right) mouse button from the text field to the code in the second pane. A blue line will appear to show the connection and a label ‘Insert Outlet or Action’ will show you what will happen and where. Let go of the drag below the line @IBOutlet weak var window: NSWindow!.

Ctrl or right drag from the UI to code to create connections
Ctrl or right drag from the UI to code to create connections

Then a small panel will appear asking for a name for the outlet connection. Enter sayThisTextField.

Enter the name, but leave everything else.
Enter the name, but leave everything else.

This will insert the following line of code:

    @IBOutlet weak var sayThisTextField: NSTextField!

In code terms this is a property of the AppController class. The @IBOutlet label tells Xcode that this property can be connected to a UI element, same as the @IBAction for the talk method. But this does not only create the proper code in the class to declare the property. The xib file also stores the instructions that this property will be set with the proper reference when the application loads. Same as the window property above which was part of the default template. Either way you look at it, you can now use the sayThisTextField property to get data from the text field.

Read More: Connecting Objects to Code – Mac Developer Library

Read More: Properties – Swift Language Guide

Change the talk method like this:

    @IBAction func talk(sender: NSButton) {
        let path = "/usr/bin/say"
        let textToSay = sayThisTextField.stringValue
        let arguments = [textToSay]

Leave the remainder of the method as it is.

Build and run the application, then enter some english text in the text field and click the ‘Talk’ button.

Make the Talk Button React to Return Key

If you are like me, you may have tried to hit the ‘return’ key to make the application say the text. It is a standard OS X behavior, that the return key activates the default button. But you need to configure our UI the right way for that to work. (Imagine a more complex application where there were more buttons. You need to tell the application which button is the default.)

To do this, select the ‘Talk’ button (1), then make sure the ‘Attributes Inspector’ tab is selected on the right side of the Xcode window (2). Among the button attributes is one called ‘Key Equivalent’. Select the field next to this label and hit the return key. It should show the return icon as the key equivalent and turn the ‘Talk’ button blue. Now you can just enter text and hit the return key to activate the ‘Talk’ button and thus our action.

Re-sizing the Window

When you build and run our application you can resize the window, but the text field and the button just stay where they are. This is not the right behavior. You can set re-sizing behavior in Xcode. Once again you need to ctrl or right drag from the object, but this time just drag towards the edge of the window which contains the object. The panel that pops up will then have options on how you want to ‘pin’ the object in the enclosing container.

Movie demonstrating how to setup Size Constraints

In the movie, normal clicks are shown as black circles and ctrl or right clicks are shown as blue circles.

You need to drag from the talk button to the right margin and upper margin. Then from the text field to the upper margin and left margin. Finally drag from the text field to the button and fix that distance as well.

When you then rebuild, then button and text field will react as you expect. You can inspect and change or delete the constraints for an object by clicking on the ruler icon in the Inspector pane on the right of the Xcode window. You can also click the constraint lines in the interface directly but they are small and hard to hit with the mouse.

Size Inspektor shows constraints
Size Inspektor shows constraints

Setting up the constraints manually is powerful, but tedious and error-prone. You can also let Xcode suggest constraints. To do this select an object and choose “Editor > Resolve Auto Layout Issues > Reset to Suggested Constraints” from the menu.

Reset to Suggested Constraints
Reset to Suggested Constraints

This will use the blue guide lines as the default constraints which is why it is important that you use them when placing objects. You can choose to reset the constraints of the selected object(s) or all objects (views) in a window. This will overwrite all constraints you may have set manually!

Read more: Auto Layout Guide – Mac Developer Library

Add a Progress Indicator

The de-activation of the talk button from in the previous part still works. But it would be nice to have some indication that the system is working on something, especially on longer texts.

Use the object library to add an “Indeterminate Circular Progress Indicatior” to your window. Place it above the right end of the text field and use the “Reset to Suggested Constraints” menu to set up the re-sizing behavior. Then disable the “Display when Stopped” behavior in the attributes inspektor.

Add a Circular Indeterminate Progress Indicator
Add a Circular Indeterminate Progress Indicator

To give the progress indicator the instructions to start and stop the animation you need to hook it up to our AppController class. ctrl- or right-drag from the progress indicator to the AppController class to insert a new @IBOutlet and name it sayProgress.

Then change the talk action method like this: (add the two lines starting with sayProgress)

    @IBAction func talk(sender: NSButton) {
        let path = "/usr/bin/say"
        let textToSay = sayThisTextField.stringValue
        let arguments = [textToSay]
        
        sender.enabled = false
        sayProgress.startAnimation(self)
        
        let task = NSTask.launchedTaskWithLaunchPath(path, arguments: arguments)
        task.waitUntilExit()
        
        sender.enabled = true
        sayProgress.stopAnimation(self)
    }

The progress indicator object has actions named startAnimation and stopAnimation. So you can tell them to take that action. Just like your talk action method you have to pass one parameter indicating the sender. When using other objects’ actions you would usually give self to pass a reference to the calling object.

Note that you use the sender parameter to address the talk button. Since the talk button is the only UI element that can is hooked up to send the talk action this is safe to do. You can also hook up the talk button as an @IBOutlet and address it directly that way.

Note: in the Xcode split view you can hover over the grey circles next to the @IB... labels and Xcode will indicate the objects this action or outlet is hooked up to. If an outlet or action is not hooked up then the grey circle will be empty.

A Choice of Voices

The default OS X text to speech voice is called ‘Alex’, but there are many more. You can configure the avilable voices in the “Dictation & Speech” pane in System Preferences. When you click on the popup next to System Voice and then select “Customize” you can choose voices for different languages. Note that the download for the enhanced voices can be quite large.

The customize voices panel in the Dictation & Speech pane in System Preferences
The customize voices panel in the “Dictation & Speech” pane in System Preferences

You can also have the say command list available voices:

say -v ?

You can tell the say command to use a different voice with the -v option

say -v Allison "hello world"

To give the user an option to choose from a list of voices, search for “popup” in the Object Library and drag the normal Pop Up Button to your SayThis Window. Also search for “label” and drag a label next to it. Change the Label to show “Voice:” and align both with other items and the blue guides. Set the suggest constraints.

Add a Pop Up Button and a Label
Add a Pop Up Button and a Label

Next create an @IBOutlet for the popup button, call it voicePopup.

Now, you can double click the popup button to edit its contents. There are three defaults and you can add more by dragging a “menu item” from the object library on to the popup button.

Popup Button with Voices
Popup Button with Voices

Then you need to add to the talk method to get the information from the popup button and pass it into the task.

    @IBAction func talk(sender: NSButton) {
        let path = "/usr/bin/say"
        let textToSay = sayThisTextField.stringValue

        var arguments = [textToSay]
        
        if let voice = voicePopup.titleOfSelectedItem {
            arguments += ["-v", voice]
        }
        
        sender.enabled = false
        sayProgress.startAnimation(self)
        
        let task = NSTask.launchedTaskWithLaunchPath(path, arguments: arguments)
        task.waitUntilExit()
        
        sender.enabled = true
        sayProgress.stopAnimation(self)
    }

First you have to change the arguments assignment to var, since you might change it later. Then you get the titleOfSelectedItem property from the voicePopup However, this is an ‘optional’, which means the value may be nothing. Swift requires you to deal with optional values, so you use a ‘conditional assignment’: if let voice =... This construct means “ if voicePopup.titleOfSelectedItem has a value, assign it to voice and do the following”.

Read More: Optionals – Swift Language Guide

If there is a value from the popup, then append it to the arguments array. (Thankfully the say command does not care about order of the options.) Otherwise it adds no arguments and uses the default voice, which you set in System Preferences.

Save the Voice choice

Every time to quit and restart the app the setting on the voice popup reverts to the first item. There may be use cases where this is appropriate. However, often you want to store settings between application launches. The class to use for that called NSUserDefaults. However, this is such a common task, that you do not even need to write code. Select the popup button and then click on the square spiral icon to show the Bindings Inspector. Click the triangle next to ‘Selected Value’ to expose the settings for that. Check “Bind to” and make sure “Shared User Defaults Controller” is selected in this popup. Leave ‘values’ in the controller key field and enter ‘voice’ as the model key path.

The Bindings Inspector for the voice popup button

With this configuration, the popup button to “binds” its selected value to the key ‘voice’ of the property ‘value’ of the ‘Shared User Defaults Controller’. This binding goes both ways, the popup button will read its initial state when starting the application from there and will write it back to there when the user changes it.

Re-build and launch the application, change the voice, quit and re-launch. The setting will persist.

Read more: User Defaults and Bindings – Mac Developer Library

Now open Terminal and enter:

defaults read com.scriptingosx.SayThis

But instead of com.scriptingosx.SayThis use the full bundle identifier you entered when creating the project in the first part. If you do not remember what you chose, you can select the blue ‘SayThis’ project icon in the left side file selector to see all you project information.

Project Information and Bundle Identifier
Project Information and Bundle Identifier

The defaults command will return the following:

$ defaults read com.scriptingosx.SayThis
{
    voice = Allison;
}

Now quit the application and enter this in Terminal:

defaults write com.scriptingosx.SayThis voice "Karen"

Then re-launch the application and it will have preset the popup to “Karen”.

The actual setting is stored in a property list file in ~/Library/Preferences/com.scriptingosx.SayThis.plist. However, it is not recommended to directly manipulate this file. The system caches preference files in memory and the file may be out of date or overwritten without your changes being read. If you access the data through the defaults command you will get the current status. If you need to reset the settings of your app for testing, you can use

defaults delete com.scriptingosx.com

Note: preferences stored this way can be managed with custom configuration profiles.

Build an Application to Run a Shell Command in Xcode and Swift – Part 1

This is a simple task but a nice project to find your way around Xcode and Swift. We will build a small Cocoa application in Xcode that executes a shell command on the click of a button.

Note: please consider supporting the author of this site by purchasing one of my books! Thank you!

For this example we will use the say command which use OS X’s text to speech to say a given text. You can try this by opening the Terminal and typing say "Hello world".

This tutorial is for Xcode 7.3 with OS X 10.11.4 El Capitan. It will probably not change too much with minor version changes, but no promises for major version differences.

All you need is a Mac with 10.11.4+ El Capitan and Xcode 7.3+ which you can download for free in the Mac App Store or Apple’s Developer page (free registration with any Apple ID required).

Creating the Project

Once you have downloaded and installed Xcode, launch it. It may prompt you for some extra installations and a password on first launch. Acknowledge those and you get to a splash screen with a few options. If you have used Xcode before it will list your previous projects. But for now, select “Create a new Xcode Project”.

1-SplashScreen

On the next step Xcode suggests many templates to build your application from. Select “Application” under “OS X” and then the “Cocoa Application” icon. Then click next to continue.

2-ChooseTemplate

In the next step you will have to fill in some identification for your applications. For the “ProductName” or the name of the application enter “SayThis”. Fill your name or organization name into the next field. The identifier in the third field should follow a “reverse DNS schema” for your organization. It is ok to use more than two segments, like “com.example.department”. If you don’t really know what to put in here use your email or github account in reverse order, i.e. “com.gmail.username” or “com.github.username”.

For the language select Swift and disable “Use Storyboards” and every other checkbox here. Our first application is going to be very simple.

3-ProjectOptions

Finally, Xcode will ask you where to save the project. Xcode will create a folder named “SayThis” with all the necessary files. If you want, you can make the project folder a local git repository for version control.

Creating the Interface

The Xcode window has a navigation area or file selector on the left, a main editor area in the center and an utility or information panel on the right. There are buttons in top right toolbar to show and hide the left and right panels.

4-PanelButtons

Right now the project itself is selected in the navigation area and the center editor shows various properties of the project. These were already set to useful defaults when the template was setup.

There are four files in this particular template. Select “MainMenu.xib”. xib files store how the interface looks like. The editor will change to a graphical area to design the interface. The application’s menu bar is at the top. However, there is no window to put an interface visible. There is a list of icons, next to the navigation bar, representing various objects in this xib file. The lowest is a window.

5-Objects

Click the icon to make the window visible in the editor area.

6-Window

In the lower right corner of the Xcode window is a list of objects that can be added to the interface. You may have to select the circle icon with a square in it to see it. You can scroll through the list, but there are so many objects that it is easier to use the search field at the very bottom.

7-ObjectPalette

Enter ‘button’ in the search then drag the “Push Button” to your window. As you drag the button around the window, you will see blue lines appear, guiding the button to the right center line or the right distance from the edges of the window. Use the blue guide lines to drop the button in the center of the window.

8-FirstButton

You can double-click the text on the button to change the default label. Let’s use “Talk”. At this time you can already “Build and Run” the project. There is a “Play” triangle button in the upper right area of the window or you can choose “Run” from the project menu. Since this is the first time to build this project it will take a bit longer.
Xcode will launch the application after building and it should show the window with the “Talk” button. You can click the button, however aside from the standard click animation, nothing will happen, since we haven’t told the button to do anything yet.

To connect the button to some action, we need to connect it to some code. We need to show the code and the UI side-by-side. There is a toolbar button on the right with two blue circles, click that and choose “Assistant Editors on Bottom” or “…on Right” (your choice) to open a second editor pane.

9-AssistantEditor

By default Xcode will show a header file we do not care about in the second panel. You can change this by clicking in the title bar of the second pane and selecting “Manual > SayThis > SayThis > AppDelegate.swift”

10-selectAppController

11-AssistantEditorWindow

The template filled the AppDelegate.swift file with some code and one property that is connected to the window. We want perform an action method in the AppDelegate when the button it clicked. To make this connection hold the ctrl-key and drag from the button to the empty space in the AppDelegate below the two template function, but above the final closing brace }. When you end the drag there a small dialog will pop up asking for specific settings. Set it to be an action, name it talk and set the sender type to NSButton.

ConnectTalkButton

This inserts an empty action method into the AppDelegate class.

    @IBAction func talk(sender: NSButton) {
    }

The @IBAction is a label for the interface builder part of Xcode to know this function is available to connect to the UI. func designates this as a function, but since this is within the definition of the AppDelegate class it is actually a class method of AppDelegate. In the brackets we define one parameter, labelled sender of type NSButton. The curly braces enclose the function code which is still empty.

Insert the following code between the curly braces:

    @IBAction func talk(sender: NSButton) {
        let path = "/usr/bin/say"
        let arguments = ["hello world"]
        
        let task = NSTask.launchedTaskWithLaunchPath(path, arguments: arguments)
        task.waitUntilExit()
    }

While you are typing Xcode will suggest completions for the code that you are typing. This can be very helpful and helps you avoid typing errors. You can hit the tab-key to accept the suggestion.

13-CodeCompletion

The let statement is very particular to Swift and declares a variable as constant. The alternative label var would tell the compiler that we plan to change the content of the variable later. Choosing let and var properly will allow the compiler to optimize the resulting code. For example in this specific case, the compiler will use a non-mutable string and array class for our arguments, since they will not change later in the code.

If you replace let with var and build then the compiler will notice you are not modifying the variable and place a warning that you should use let instead.

14-letwarning

Since the say command will not run within a shell and we cannot rely on environment variables being set, especially the PATH variable, we need to give the full path to the say command. To figure out the full path to a command you can use the which command in Terminal.

$ which say
/usr/bin/say

The arguments are passed as an array of Strings. Right now we have only a single static argument, but we could pass more, each option or argument will be its own String in the array. so if you wanted to use another voice you could extend the array to

let arguments = ["hello world", "-v", "Kathy"]

(One String per argument, no need to escape spaces.)

Finally we use the NSTask class to create and launch the command. Then the waitUntilExit() method of NSTask pauses code execution until the command finished.

There is a minor problem in the UI. If you hit the button quickly in succession, you will get multiple “hello worlds” on top of each other. One solution to that is to disable the button while the task is being processed. Alle interface elements have an enabled property we can use for that purpose. Change the talk method to this:

    @IBAction func talk(sender: NSButton) {
        let path = "/usr/bin/say"
        let arguments = ["hello world"]
        
        sender.enabled = false
        
        let task = NSTask.launchedTaskWithLaunchPath(path, arguments: arguments)
        task.waitUntilExit()
        
        sender.enabled = true
    }

Before we execute the task, we disable the button, then enable it later. Now, when you click the button it will be disabled while the task is running and be re-enabled afterwards.

Congratulations! You have built a simple OS X Application. In the next part, we will hook up a few more UI Elements to give the app some more functionality.

Continue to Part 2