Category: SwiftUI

Document Types in SwiftUI Apps

SwiftUI supports making document-based apps that let people create and save documents. To ensure the documents have the right file extension and save and load correctly, you must configure the app’s document types. There’s not much information online about document types in SwiftUI apps so I’m sharing what I learned in this article.

Accessing the Document Type Settings

Take the following steps to access the document type settings for your SwiftUI project:

  1. Select the project file from the left side of Xcode’s project window to open the project editor.
  2. Select your app from the target list on the left side of the project editor.
  3. Click the Info button at the top of the project editor.

DocumentTypeSettings

There are three sections of document type settings.

  • Document Types
  • Exported Type Identifiers
  • Imported Type Identifiers

A new SwiftUI document-based app project gives you a plain text editor. Unless you’re making a plain text editor, you must change the document type settings.

Document Types

Every document type in a SwiftUI app requires you to supply the following information:

  • Name
  • Identifier
  • Handler Rank

The name describes the document. Enter a descriptive name in the text field.

The identifier uniquely identifies the document type. An iOS app has a Types text field to enter the identifier. Apple has a list of system defined types for common file types. But you can also define your own type using the following convention:

I found in an app I’m developing that the document had the wrong file extension and type on the Mac until I made the DocumentName part of the identifier match the file extension for the document. I didn’t have this problem on iOS.

The handler rank tells Xcode whether your app owns the document type. In most cases you can choose Default.

Mac document types also require you to choose whether your app can edit documents of that type or just view them. Choose Editor to let people edit documents in your app.

Exported Type Identifiers

You need an exported type identifier for each document type your app owns. If you create a custom document type for your app, you must add an exported type identifier for the custom document type. Do not add exported type identifiers for file types your app exports.

You must supply the following information for an exported type identifier:

  • Description
  • File extension
  • Identifier
  • Conforming identifiers

If you are adding a description for a custom document type, the description usually matches the name of the document type.

Enter the file extension without the leading dot in the Extensions text field.

The identifier should match the identifier for the document type.

You may be able to avoid entering conforming identifiers, but most document types require them. The conforming identifiers are a list of identifiers the type identifier conforms to. For example if you have a custom document type that saves the document in a file package, it must conform to com.apple.package. If you look at the list of system defined types, the Apple System Base Types section has the most common conforming types.

There are also fields to enter a MIME type and a reference URL for the exported type identifier. If your document type has a MIME type or a reference URL, enter them in the appropriate fields.

Imported Type Identifiers

Imported type identifiers are for types your app uses but doesn’t own. Xcode provides an imported type identifier for your document type. If your app imports other file types, you must add imported type identifiers for the other types. If you’re making an image editor, you would add imported type identifiers for the image file formats your app supports, such as PNG and JPEG files.

You supply the same information for imported type identifiers as you do for exported type identifiers so I’m not going to repeat the information here.

SwiftUI Code for Document Types

Open the Swift file for the document struct and you should see the following code:

If you changed the document type, you should replace the string com.example.plain-text with the identifier for your app’s document type. You should also change the variable name exampleText to something that better describes your document type.

Notice that the init for UTType has an importedAs argument. The UTType class reference in Apple’s documentation has a list of inits you can use for your document types.

The readableContentTypes property contains an array of the document types your app can read. There should be an array entry for each imported type identifier in your app. Apple has Swift enums for common document types.

SwiftUI documents also have a writableContentTypes property. This property defaults to matching the readable content types. If your app exports to a type that is not in readableContentTypes, you must add a variable for the writable content types and supply the writable types.

Summary

The most important points about SwiftUI document types are the following:

  • Document types must have a unique identifier.
  • Add exported type identifiers for any custom document types you make.
  • Add imported type identifiers for any file types your app can import.
  • You need a UTType property in your code for the document type.
  • You need to supply a readableContentTypes array in your code with an entry for each imported type identifier.

I have a WikiDemo project on GitHub that has its own document type. Clone the project to examine the settings for the document type, exported type identifiers, and imported type identifiers.

Disable a Text Field in a SwiftUI List Until Tapping Edit Button

SwiftUI lists support using text fields to change the name of list items. But if your list items are navigation links, you will run into some annoying behavior on iOS. You tap a list item expecting to go to the navigation link destination, but you end up changing the name of the list item.

When you tap a list item that is a navigation link, you normally want to go to the link destination. But you still want to be able to rename list items. In SwiftUI iOS apps, you can disable the list item’s text field until someone taps the Edit button. In edit mode you can tap the list item to rename it. When the person taps the Done button, disable the text field.

Variables to Add to the SwiftUI View

Start by adding two variables to your SwiftUI view that has the list. The first variable is an environment variable for the editing mode. This variable tracks when someone taps the Edit and Done buttons.

The second variable is a Boolean value that tracks if the text field is disabled. The name disabled is used by SwiftUI. I got a compiler error when I named the variable disabled so use another name for the variable.

The text field should be disabled until someone taps the Edit button.

Modifiers to Add to the Text Field

Add two modifiers to the text field. The first modifier is the .disabled modifier. Supply the Boolean variable you added to the view.

The second modifier is the .onChange modifier. The change you’re going to track is the change in edit mode. When someone taps the Edit button, the isEditing property is set to true. Set the Boolean variable to false, which enables editing in the text field. When someone taps the Done button, isEditing becomes false. Set the Boolean variable to true, which disables editing in the text field.

Sample Project

I have a sample project on GitHub. Look at the PageListView.swift file in the iOS folder to see the code for disabling the text fields in the list.

Moving List Items Using Drag and Drop in SwiftUI Mac Apps

Mac apps usually use drag and drop to rearrange items in a list. You search for how to move list items in SwiftUI, and you find a bunch of examples for iOS that use the .onMove modifier. But when you start to type .onMove in your Mac list, Xcode’s autocomplete shows only an .onMoveCommand modifier. If you try to use .onMove directly on a list in a Mac app, you’ll get a compiler error.

SwiftUI has an .onMoveCommand modifier to move items in a list in a SwiftUI Mac app, but it works with the keyboard, not with drag and drop. How do you use drag and drop to move items in a SwiftUI list in a Mac app?

.onMove Requires ForEach on Mac

The .onMove modifier is the modifier to use to move list items using drag and drop in SwiftUI Mac apps. But you must place a ForEach statement inside the list to enable .onMove. The ForEach statement takes two arguments: the array of items you’re showing in the list and an ID that uniquely identifies each list item.

Apply the .onMove modifier to the ForEach block. The .onMove modifier’s closure takes two arguments: the indices for the list items being moved and the drop destination. Call the array’s move method to reorder the list items.

The following code creates a list of a book’s chapters that you can rearrange using drag and drop:

Accessing the Document in a SwiftUI Menu

You’re making a SwiftUI document-based Mac app. You have a menu item in your app that performs an action on the document. How do you give the menu access to the document?

Use focused values and focused bindings.

Creating a Focused Value

A focused value provides a way for a SwiftUI app to observe values from the focused view or one of its ancestors. In a document-based SwiftUI Mac app, one of the focused view’s ancestors is the document window. By using a focused value your app can access the focused document.

To create a focused value, you must write two pieces of code. The first is a struct that conforms to the FocusedValueKey protocol. The second is a property for the document as an extension to the FocusedValues struct.

The struct creates a type alias for the document’s type, which is usually a binding to your document type.

The document variable is the value you will use when setting the focused value. The value must match this variable name.

Notice the type of the variable, DocumentFocusedValueKey.Value?. The first part of the type is the name of the struct you created for the focused value. The second part is the name of the type alias you created in the struct.

Setting a Focused Value

The .focusedValue modifier sets a focused value.

The name of the first argument must match the name of the variable you created in the FocusedValues extension.

Apple added the .focusedSceneValue modifier in iOS 15 and macOS 12. This modifier works much better than .focusedValue, which requires the person using the app to be focused on a text view or text field. If you can require iOS 15 and/or macOS 12, use .focusedSceneValue.

Where do you place the code to set the focused value? Attaching the focused value modifier to the content view in the app file is the most common place in a document-based SwiftUI app.

Focused Bindings

A focused binding gives a SwiftUI view access to the focused value. To create a focused binding, declare a variable with the @FocusedBinding property wrapper and supply the name of the focused value in parentheses.

Using Focused Bindings in SwiftUI Menus

To use a focused binding in a SwiftUI menu, you must create a SwiftUI view for the menu items. Create the menu items in the group. The following example shows a menu with items to make text bold and italic:

Creating Menu Commands

If you have a menu with multiple menu items, creating a set of menu commands lets you keep the menu creation code in its own Swift file. To create a set of menu commands, supply the views inside the CommandMenu block.

Add the Menu to the App

The final step is to add the menu to the app.

By creating a struct for the menu commands, the code inside the app’s body is much cleaner.

Credits

I learned much of the information shared in this article from the following article by Lost Moa:

Accessing the document in the SwiftUI macOS menu commands

Creating a Master-Detail Inteface in SwiftUI

Master-detail interfaces are common in iOS and Mac apps. Select an item from the master view to see additional information in the detail view. In SwiftUI you use two views to create a master-detail interface: NavigationView and NavigationLink.

A navigation view is the most common way to create a master-detail interface in SwiftUI. On iOS selecting an item from the master view, which is usually a SwiftUI list, takes you to the detail view. On macOS selecting an item from the master view shows the details in the detail view.

The following code shows how to create a navigation view:

In a real app you will pass data as arguments to the master view and detail view. The data depends on your app, which is why I didn’t supply any arguments in the code listing.

The final part of creating a master-detail interface is to add a navigation link in the master view and set its destination to the detail view.

This example creates a navigation link for each item in the list. Selecting an item from the list fills the detail view with information about the selected item. In a real app you will pass the data to show in the detail view as an argument to the detail view.

Handling Selection

There are some situations where you may need to hold on to the selection. Mac apps need access to the selected item when deleting an item from a list.

In the master view create a property to store the selection. Make it optional and set its value to nil.

When someone selects an item from the list, the selectedItem property will store it. In the call to create the navigation link, add the tag and selection arguments. The tag is usually the current item. The selection is the selected item.

Sample Project

I put a sample project on master-detail interfaces on GitHub. It builds upon the project from the Make a Markdown Editor in SwiftUI article by displaying a list of Markdown pages to edit. Look at the files ContentView.swift and PageListView.swift for the code on making the master-detail interface.

Using a Scrollable Text View in a Mac SwiftUI App

In the article Using Text Views in a SwiftUI App I showed how to use a UIKit text view in a SwiftUI app. But if you use the code from that article in a Mac app, you’ll run into a problem. The text view won’t scroll when you reach the bottom of the text view. In this article you’ll learn how to make the text view scroll in a Mac app.

Much of the code for this article comes from the CodeEditor Swift package, which is a text editor for SwiftUI with syntax highlighting.

Create a Scroll View

The reason the text view won’t scroll is that Mac text views aren’t wrapped in scroll views like iOS text views are. When you create the text view, you have to create both a text view and a scroll view. Set the scroll view’s document view to the text view. Give the scroll view a vertical scroller. Return the scroll view.

Setting the autoresizing mask ensures the text view resizes properly when the window resizes.

Updating the View

When writing the updateNSView function, supply the scroll view as the argument. Use the documentView property of the scroll view to access the text view and update its contents.

Removing Items from SwiftUI Lists in Mac Apps

Most examples of removing items from SwiftUI lists use the .onDelete handler, which is not available for Mac apps. In this article I share what I learned to remove list items from SwiftUI Mac apps.

To remove items from SwiftUI lists in Mac apps, you must perform the following tasks:

  • Add a variable to the list view to store the selected list item.
  • If you are using a navigation link, supply a tag and selection when creating the link.
  • Make your struct or class conform to the Equatable and Hashable protocols.
  • Add the .onDeleteCommand handler to the list. The .onDeleteCommand handler is the handler SwiftUI Mac apps use to remove list items.

Add a Selection Variable to the List View

To remove an item from a SwiftUI list, the list view requires a variable to store the item you want to remove. Create an optional for the variable and set it to nil initially.

ListItemStruct is the name of the data structure in your app that you want to show in the list.

When you supply this selection when creating a navigation link, SwiftUI keeps track of the selected item in the list.

Most SwiftUI apps that use lists use a navigation link to create master-detail interfaces. Select an item from the list to show additional information in the detail view. Add a call to NavigationLink in the master view and set its destination to the detail view.

To support more complex selection behavior, you must supply two additional arguments to the navigation link call: tag and selection. Usually the tag is the current list item you’re adding to the list. The selection is the variable you added to the list view.

The following code demonstrates how to show a list of a book’s chapters:

This example uses the improved syntax Apple added in Xcode 13 to bind list text fields to items in an array. If you’re using Xcode 12 you will have to use a Text to display the titles and remove the $ character from $chapter.

Make Your Struct/Class Conform to Equatable and Hashable Protocols

To use the tag and selection arguments in a navigation link, your struct or class must conform to the Equatable and Hashable protocols. Your project won’t compile until you make the struct or class conform to those protocols.

Making your struct or class conform to Equatable requires you to implement the == operator to check for equality.

Replace Chapter with the name of your struct or class. Do whatever comparisons you need to make to determine that two objects are equal. SwiftUI list items require a unique ID. That’s what I used to determine equality in the example.

To conform to the Hashable protocol, you must implement the hash function.

Inside the hash function, call the hasher’s combine function for each property in your struct or class. Supply the name of the property.

Add the .onDeleteCommand Handler to the List

The last step is to remove the item from the list. Add the .onDeleteCommand handler to the list to enable the Delete menu item in the Edit menu. Inside the block of code, you will use the selection variable you added to the list view to find the selection index. Use the selection index to remove the item from the list.

The firstIndex function returns the first selected item in the list. After getting the index of the selected item, remove that item from the array that populates the list.

Now let’s put the whole list view together.

Removing an Item with a Button and the Delete Key

At this point you can remove a list item by choosing Edit > Delete. But you may want to provide a button to remove an item. How do you remove list items by clicking a button?

Start by moving the code inside the .onDeleteCommand handler into its own function. Moving the deletion code into a separate function will also make the list code cleaner.

Now the .onDeleteCommand handler looks like the following:

Call the function in your button. Add a .keyboardShortcut handler to the button to remove list items with the Delete (Backspace) key.

I haven’t figured out how to add a keyboard shortcut for the Delete menu item in the Edit menu. Every example I’ve seen on creating keyboard shortcuts for menu items in SwiftUI uses custom menu items, not the menu items that Apple supplies. I’ll update the article if I ever find a solution.

Sample Project

I have a project on GitHub that supports removing items from lists. Look at the PageListView.swift and Wiki.swift files for the list removal code.

Another sample project for SwiftUI list item removal is the Feed Read project by TrozWare for the Back to the Mac conference.

Should I learn Swift or SwiftUI?

I see a lot of new iOS developers ask the question in the title of this article. The short answer is both. To write SwiftUI apps you must also learn Swift because Swift is the programming language SwiftUI uses. The rest of this article provides a more detailed explanation.

UIKit

In 2008 Apple gave developers a SDK (Software Development Kit) to let them make native iOS apps. The heart of the SDK was UIKit, a framework for creating the views and controls in iOS apps, such as buttons, text fields, and table views.

UIKit uses the Objective-C programming language. Using Objective-C worked well for existing Mac developers, who were already using Objective-C to make Mac apps. But the release of the iOS SDK attracted lots of new developers to the Apple developer community. These new developers found Objective-C’s syntax to look strange and found it difficult to understand. They wanted a language with a syntax that looked more familiar.

Swift

In 2014 Apple unveiled their solution for developers who hated Objective-C: the Swift programming language. Swift’s syntax looked more familiar to people who came to iOS development from web development and Windows development. Now iOS developers had two language choices for making iOS apps with UIKit: Swift and Objective-C.

SwiftUI

In 2019 Apple released the initial version of SwiftUI, a new framework for developing apps for all of Apple platforms: iOS, Mac, tvOS, and watchOS. SwiftUI has only one language: Swift. You must know Swift to use SwiftUI.

The Language and Framework Options for iOS Apps

Someone who wants to make iOS apps with Apple’s frameworks has three options.

  1. Use UIKit with Objective-C.
  2. Use UIKit with Swift.
  3. Use SwiftUI with Swift.

Which option should use choose? You won’t be making a mistake no matter which option you choose. But for someone new to iOS development, I recommend Option 3, write the app with SwiftUI using Swift. SwiftUI is the future of iOS development. You’re eventually going to have to learn it so you might as well learn it now.

Make a Markdown Editor in SwiftUI

In this tutorial you will make a Markdown editor with live preview using SwiftUI. This editor will run on both iOS and Mac. It’s a nice example to demonstrate how to create a document-based, multi-platform SwiftUI app. Plus, it shows how to use a WebKit web view in SwiftUI.

This tutorial uses the new document-based app features Apple added in Xcode 12. You must be running Xcode 12.2+ to create a multi-platform SwiftUI app. The iOS app requires iOS 14+, and the Mac app requires macOS 11+. If you are running macOS 10.15 (Catalina) on your Mac, you can still make the editor. You won’t be able to run the Mac version.

To keep the tutorial from getting too long, I will gloss over some steps and explanations that I covered in the following articles:

Create the Project

Start by creating the project.

  1. Choose File > New > Project in Xcode.
  2. Click the Multiplatform button at the top of the New Project Assistant.
  3. Choose Document App from the list of application templates.
  4. Click the Next button.
  5. Name the project in the Product Name text field.
  6. Click the Next button.
  7. Choose a location to save the project.
  8. Click the Create button.

If you look at the project navigator, you will see Xcode creates the following folders for your project:

  • The Shared folder contains files that both the iOS and Mac app targets use.
  • The iOS folder contains files that the iOS app uses.
  • The Mac folder contains files that the Mac app uses.

In the Shared folder are Swift files for the app, document, and content view.

Run the project and you will see that you have a working plain text editor. You can create documents, edit text, save documents, and load documents.

Add the Ink Package

This project uses the Ink Markdown parser to convert the Markdown you type in the text editor to HTML that you will preview. Ink has Swift Package Manager support to simplify adding it to your Xcode project.

Select the name of your project from the project navigator to open the project editor. Select the project from the project editor and click the Swift Packages button at the top of the editor to add the Ink package.

A current limitation in Xcode’s Swift Package Manager support is you can add a package to only one target initially. To add Ink to the other app target, select the target from the project editor and add the Ink framework from the Frameworks, Libraries, and Embedded Content section.

AddSwiftPackageToSecondTarget

Add Web Views

To preview the Markdown you write, you need a web view to display the HTML. SwiftUI does not currently have a native web view so you must use a WebKit web view, WKWebView, for the preview.

WKWebView has both iOS and Mac support, but you’re going to have to create two web view files: one for the iOS app and one for the Mac app. The code is going to be almost identical. The reason you need two files is that SwiftUI has separate protocols for working with UIKit(iOS) and AppKit(Mac) views.

Create one new Swift file in the iOS folder in the project navigator and create a second file in the Mac folder. Make sure the file in the iOS folder is a member of the iOS app target. Make sure the file in the Mac folder is a member of the Mac app target. You can set the target membership for a file using the File Inspector on the right side of the project window.

Add the following code to the iOS Swift file:

The web view uses the SwiftUI and WebKit frameworks so you must import them. When you use a UIKit view in a SwiftUI app, the view must conform to the UIViewRepresentable protocol. The html property stores the HTML to display in the web view.

There are three functions. The init function initializes the web view with some HTML to display. The makeUIView function creates the web view. The updateUIView function loads the HTML string to show in the web view.

The Mac code is almost identical. Replace anything starting with UI with NS.

Parsing the Markdown

The next step is to write some code to parse the Markdown to HTML. Open the ContentView.swift file. Import the Ink framework.

Add the following computed property to the ContentView struct:

This code creates an Ink parser and calls a function that converts the document text into HTML. This code is much easier to write than creating your own Markdown parser.

Build the User Interface

The last step is to build the user interface. The user interface contains a text editor and a web view side by side.

The body property for the content view should look like the following code:

The code creates a horizontal stack so the text editor and web view are side by side. The text editor is on the left and contains the document’s text. The web view is on the right and displays the HTML you parsed from the Markdown text. The iOS app uses the iOS version of the web view. The Mac app uses the Mac version of the web view.

Run the project. Any Markdown you type in the text editor will appear as HTML in the web view. The Ink parser does not currently support creating code blocks with indentation. You must add three backticks on the line above and below the code to create a code block.

I have the project on GitHub for you to look at if you run into problems.

Creating Document-Based Apps with SwiftUI

Xcode 12 Note from the Author

Xcode 12 made a bunch of changes to SwiftUI for document-based apps. If you choose a multi-platform document app project, you will get the text editor project I create in this article without having to write any code. I’m keeping this article up for people who are still using Xcode 11.

The article Make a Markdown Editor in SwiftUI shows how to create a document-based SwiftUI app with Xcode 12.

Start of Original Article

I have not seen any articles or tutorials on creating a document-based app with SwiftUI so I’m writing one. In this tutorial you will build an iOS plain text editor.

If you haven’t already, I recommend reading two articles before going through the tutorial. Creating Document-Based iOS Apps Part 1 provides an overview of creating document-based iOS apps. Using Text Views in a SwiftUI App provides an explanation of using a UIKit text view in a SwiftUI app. SwiftUI does not currently have a built-in text view.

Create the Project

Start by creating a project. Create an iOS document-based app project. Choose SwiftUI from the User Interface menu if it’s not already selected.

The most interesting files Xcode creates for a document-based SwiftUI app are the following:

  • DocumentBrowserViewController.swift contains code for the document browser, where people create and open documents.
  • DocumentView.Swift contains code for the document’s main view.
  • Document.Swift contains code for the document.

Creating a New Document

If you run the project, you’ll notice that tapping the Create Document button does nothing. You must write some code to create the document when someone taps the button. The easiest way to create a new document is to add an empty file to the project. The empty file should have the same file extension as the document’s. This file will be copied to the app bundle when building the project. You’ll have to write some code to load the file from the app bundle.

One last thing to do to create documents properly is to configure the document type in Xcode so that the app is an editor of plain text files.

Add an Empty Document File

Choose File > New > File to add a new file to the project. Select Empty from the list of iOS file templates. The empty file is in the Other section. You have to scroll down a bit to reach the Other section.

Name the file. I named the file New Document.txt. You can choose a different name, but remember the name.

Load the Empty Document

Open the DocumentBrowserViewController.swift file and go to the didRequestDocumentCreationWithHandler function. Replace the following line of code:

With the following code:

This code loads the empty document file from the app bundle and uses that as the base for a new document.

There is one more piece of code to change. In the same function, find the following code:

There is a problem with the code inside the if block.

This line of code moves the file from the application bundle. Your app will crash the second time you create a document because the empty document file was moved out of the application bundle. The fix is to copy the file from the application bundle when creating a new document.

Edit the Document Type

Xcode initially sets the document type for an iOS document-based app to be a viewer of image files. You must configure the document type in Xcode so that the app is an editor of plain text files. You’re making a text editor, not a text viewer.

Select the project from the project navigator to open the project editor. Select the app target from the left side of the project editor. Click the Info button at the top of the project editor to access the document types. Click the disclosure triangle next to Document Types.

DocumentTypes

  1. Enter PlainText in the Name text field.
  2. Enter public.plain-text in the Types text field. public.plain-text is the UTI (Uniform Type Identifier) for plain text files.
  3. In the Additional document type properties section, set the CFBundleTypeRole value to Editor so people can edit documents.
  4. Set the LSHandlerRank value to Alternate to ensure this text editor isn’t the default text editor for all plain text files.

Create the Data Model

The data model for this project is simple. The document is the data model. All you have to do is add a property to store the text. Open the Document.swift file and add the following code inside the Document class:

The code declares a property to store the text and has the initial value of an empty string.

Building the Text View

Now it’s time to add the text view so people can edit text. Currently SwiftUI does not include a text view so you have to write code to create a UIKit text view. But it’s not too much code. Add a new Swift file to your project for the text view. Import the SwiftUI and UIKit frameworks. Add the following struct:

The text view must conform to the UIViewRepresentable protocol, which is the protocol that allows the use of UIKit views in SwiftUI apps. To conform to the protocol, you must write the following functions:

  • makeUIView
  • updateUIView
  • makeCoordinator

The makeUIView function creates and configures the view. The function takes an argument of type Context and returns the type of view you want to make, which is UITextView for a text view. The Context type is a type alias for the context where updates to the UIKit view take place.

The code listing creates a text view, configures the view so people can edit large amounts of text, and adds some padding so the text isn’t on the left edge of the screen. The code also sets the view’s delegate to the context’s coordinator, which you will create shortly.

The updateUIView function handles updates to the view.

I will fill in this function later.

The makeCoordinator function creates a coordinator so the UIKit view can communicate with data in SwiftUI.

Create the Coordinator

Add a Coordinator class inside the struct for the text view.

The class inherits from NSObject, which is the base class for all UIKit classes. A text view’s coordinator should conform to the UITextViewDelegate protocol so it can respond to text view notifications, such as the text changing.

The coordinator needs a property to hold the UIKit view and an initializer. I will be adding more to the coordinator later in the article.

Add the Text View to the Document View

The last step to adding the text view is to have the document view display it. Open the DocumentView.Swift file. Inside the body property you should see a VStack that contains a HStack and a button. The HStack shows the name of the file. The button lets you go back to the browser when you’re done writing.

The text view should appear between the HStack and button. Add the following line of code between the HStack and button:

If you build and run the project, you should be able to create a new document and type in it.

Connect the Text View to the Document

For the app to do more than let people type text in a text view, you must connect the text view to the document so the text you type updates the document as well. In the document view, you should see the following variable:

This variable contains a reference to the document. Make the following changes to the variable:

The @State property wrapper will allow the text view to bind to the document in order to display the document’s text. Changing the type of the variable to Document is also necessary for the text view to work with the document properly.

Now add the following property to the text view:

The @Binding property wrapper binds the document property in the text view to the document property in the document view. The text view and document view are both pointing to the same document. The text view now has access to the document.

Now that you created the binding you must go back to the document view and change the call to create the text view by supplying the document as an argument.

The $ at the start of $document indicates that you are passing a binding to the text view. You must pass a binding so the document view and text view both point to the same document.

Fill the updateUIView Function

Now that the text view has access to the document, you can write the text view’s updateUIView function. Set the text view’s contents to the document’s contents.

Handling Text Changes

One last thing to do is to update the document when the text view contents change. Add the following function to the Coordinator class:

The first line of code sets the document’s contents to the text view’s contents. The second line marks the document as changed so it will be saved.

Save the Document

At this point you’re finished with the SwiftUI material, but there’s still some work to do to finish the app. The text editor is missing one really big feature: saving text. Open the Document.Swift file. Xcode created a blank contents function for saving the document.

What you have to do is convert the text in the document to a Data object and archive that object. Apple provides the NSKeyedArchiver class and an archivedData function so you can do both steps in one line of code.

The root object is the document’s text. Requiring secure coding ensures your app will be able to unarchive the data when loading the document.

Load the Document

After saving the document, the next task is to load the document when someone chooses a document from the browser. Xcode supplies a blank load function, where you write the code to load the document from disk.

The first argument to the load function is the contents of the file. You must first cast the contents to the Data type. Call the NSKeyedUnarchiver class’s unarchiveTopLevelObjectWithData function to unarchive the text from the file. The last step is to set the document’s text to the contents of the file.

Conclusion

Now you have a simple, working text editor. You can create documents, edit text, save documents, and open them. You can use this project as a foundation for building your own text editing app, such as a Markdown editor. I have the project on GitHub for you to download if you run into issues.