Apple provides the WKWebView class to show web content in Swift apps. Most apps use web views to show content from websites, but you can also show local HTML in a web view. There are two common ways to show local HTML in a web view.

• Loading HTML strings
• Loading HTML files

Loading HTML Strings

The easiest way to display HTML content in a web view is to create a string for the HTML and call the loadHTMLString function.

A common reason to load an HTML string is to preview Markdown content. You can see examples of loading HTML strings in my WikiDemo and SwiftUIMarkdownEditor GitHub projects.

The biggest limitation of loading HTML strings and showing them in a web view is that images will not show. Inserting images in a HTML string is a security risk so the web view won’t display them.

Loading HTML Files

If you want to show images in a web view, you must create a HTML file and show it in the web view by calling the loadFileURL function. The function takes two arguments. The first argument is the URL of the file to show in the web view. The second argument is a URL that you give the web view access to read. You normally give read access to a folder that contains subfolders you want to show, such as image and CSS files.

I recently added code in an app to preview EPUB books in a web view. An EPUB book has an OEBPS folder that holds most of the book’s content. The OEBPS folder has the following subfolders:

• A Text folder that contains the book’s chapters.
• An Images folder that contains the book’s images.
• A Styles folder that contains any CSS files to style the book.

To preview the book I needed to pass the URL of the current chapter’s HTML file as the first argument to loadFileURL and the URL of the OEBPS folder as the second argument. Giving the web view access to the OEBPS folder gives the web view access to the images and CSS files.

The Keychain is the place to store small amounts of data securely, such as passwords and API tokens. In this article you’ll learn how to work with the Keychain in iOS and Mac apps using the Keychain Services framework.

Parts of a Keychain Action

There are four common actions to perform on keychain items: add an item, update an item, read an item, and delete an item. To perform a keychain action, create a query and run a Keychain Services function.

Query

A query tells Keychain Services what you want to do. A query is a Swift dictionary that you must cast to CFDictionary.

Every query must include an entry with the key kSecClass, which specifies the kind of item to add, update, read, or delete. There are the following Keychain item types:

• Generic password, kSecClassGenericPassword
• Internet password, kSecClassInternetPassword
• Certificate, kSecClassCertificate
• Cryptographic key item, kSecClassKey
• Identity item, kSecClassIdentity

I’m going to focus on generic passwords in this article, as that’s what most apps use. You’re not limited to passwords when using generic passwords. I was able to use generic passwords to store OAuth tokens in the Keychain.

The query keys you can use depend on the class. You can find a list of possible keys in the following section of Apple’s documentation:

Item Class Keys and Values

Click the link for a class to see the available items. You can also read the documentation in Xcode by choosing Help > Developer Documentation.

Two common item attributes for generic passwords are services, kSecAttrService, and accounts, kSecAttrAccount.

The value you supply for the service is the text that appears for the item in the Keychain Access app on Mac. Make sure the text clearly shows the keychain item is part of your app. A generic value like password will be hard to find in the Keychain Access app.

The value for the account is the name of the password’s account. If you’re writing a Twitter client, Twitter would be a good value for the account.

Keychain Services Functions

Call the following functions to work with the Keychain for passwords:

• SecItemAdd to add an item to the Keychain
• SecItemUpdate to update an existing Keychain item
• SecItemCopyMatching to read an item from the Keychain
• SecItemDelete to delete an item from the Keychain

Adding a Keychain Item

Start by importing the Authentication Services framework. The Keychain Services API is in the Authentication Services framework.

You should also create a class for the Keychain functions.

Let’s start by writing a function to add an item to the Keychain.

The function starts by building a query. Tell Keychain Services that you’re adding a generic password. Supply the data, service, and account. The data is what you want to save in the Keychain.

After building the query, call the function SecAddItem to add the item to the Keychain. If the item is added to the Keychain successfully, SecAddItem returns the value errSecSuccess.

If the item already exists in the Keychain, SecAddItem returns the value errSecDuplicateItem. In this case update the existing item, which I cover next.

Updating an Existing Keychain Item

Let’s look at the code to update a keychain item.

Notice that the update function doesn’t include the data in the query. The code creates another dictionary for the data and passes it as an argument to the function SecItemUpdate.

Reading an Item from the Keychain

Saving items to the Keychain isn’t going to help unless your app can read the keychain items.

The big difference in the query is the kSecReturnData key, which tells Keychain Services you want to return data from the function call. The function SecItemCopyMatching returns its results as type AnyObject?. You saved the item as Data so you should return a Data object. If there is no matching item in the Keychain, SecItemCopyMatching returns nil.

Deleting an Item from the Keychain

The last major task to perform on Keychain items is to delete items from the Keychain.

The query for deleting an item is the simplest one. Supply the class, service, and account. Call SecItemDelete to delete the item from the Keychain.

What Is a File Wrapper?

A file wrapper is a bundle, which is a collection of one or more directories (folders) and files that appears as a single file in the Finder (Mac) or Files app (iOS). Most Mac applications use bundles. If you want to see what a bundle looks like, select an application, right-click, and choose Show Package Contents.

When should you use a file wrapper? Use a file wrapper when you want to save your app’s data in multiple files. Suppose you’re developing a website building app. A website can have multiple pages, plus folders and files for images, videos, and custom CSS. By using a file wrapper you can save all these files and have it look like a single file to the person using the app. Most apps don’t need to use file wrappers

Types of File Wrappers

The FileWrapper class has the following file wrappers:

• Directory
• Regular file
• Symbolic link

The symbolic link file wrapper points to a file. The most common case of using a symbolic link file wrapper is to point to a large file (image, audio, or video file) to keep the wrapper from getting too big. I’m going to focus on directory and regular file wrappers in this article.

Making Your File Wrapper Appear as a Single File

Document-based apps are more likely to use file wrappers than shoebox apps. If you forget to configure the document to be a file wrapper, the document will appear as a folder instead of a single file.

To configure the document to be a file wrapper, perform the following steps:

1. Select the project from the project navigator to open the project editor.
2. Select the app from the Targets list in the project editor.
3. Click the Info button at the top of the project editor.
4. Click the disclosure triangle next to the Exported Type Identifiers section in the project editor.
5. Enter com.apple.package in the Conforms To text field.
6. Click the disclosure triangle next to the Imported Type Identifiers section in the project editor.
7. Enter com.apple.package in the Conforms To text field.

Creating a Document File Wrapper

You must create a file wrapper when saving the document. If you create a document-based SwiftUI app, you should see the following function in the document struct’s Swift file:

This function is called when saving the document. Your code to create the file wrapper goes in this function.

To create a file wrapper you must perform the following tasks:

• Create a directory file wrapper
• Convert your app’s data to a Data object
• Create a regular file wrapper
• Add the file to a directory file wrapper

Creating a Directory File Wrapper

At a minimum you must create a root directory for the file wrapper. You will return this wrapper in the call to fileWrapper. To create a directory file wrapper, call the FileWrapper method directoryWithFileWrappers and supply an empty Swift dictionary.

Call directoryWithFileWrappers and supply an empty dictionary for any additional directories you want to create.

The root directory of a wrapper does not need a name because it does not appear in the Finder or Files app. But any other directories you create require a name. Set the preferredFilename property to name the directory.

Call the addFileWrapper method to add the directory to the root directory.

Convert App Data to a Data Object

Files in file wrappers store their data in a Data object. You must convert your app’s data to Data to use file wrappers. Converting to Data depends on what you are storing, but the following code converts a string to Data:

Creating a Regular File Wrapper

To create a file wrapper for a regular file, call the FileWrapper method regularFileWithContents and supply the Data object that contains the file’s data.

Set the preferredFilename property to name the file.

In a real app you won’t be hardcoding filenames often. Suppose you have a document that has a list of pages. You would use the page’s title as the filename instead of giving the file a specific name. Remember that you use file wrappers to save multiple files. If you have 20 files to save, hardcoding the name of each file is going to be a pain. The following code demonstrates how to save a collection of text files:

Call addFileWrapper to add a file to a directory.

Reading from a File Wrapper

At this point you know how to create a file wrapper and save data to it. The next step is to read data from the file wrapper when opening a document.

The SwiftUI document structure provides the following initializer to read data from a file wrapper:

This initializer is where you add the code to read from the file wrapper. To read from a file wrapper, you must perform the following tasks:

• Access the directory holding the files
• Read the individual files
• Load the data from the file

Access the Directory Holding the Files

If you store all the files inside the root directory, you won’t need to write any code to access the directory. But if you have files inside a subdirectory, you must call the fileWrappers method and supply the name of the subdirectory as the dictionary value.

The SwiftUI initializer takes a read configuration as an argument. The ReadConfiguration struct has a file property that provides access to the root directory of the file wrapper.

Reading the Individual Files

Use the fileWrappers property to access the files in a directory file wrapper. Go through each file and load the data. Use the regularFileContents property to access the file contents.

Loading the Data

The file wrapper’s regularFileContents property gives you a Data object to load the file’s contents in your app. Loading the file’s contents depends on the type of data being stored. The following code loads a file’s contents into a string variable:

Sample Project

I have a sample project on GitHub that demonstrates saving data to a file wrapper. Look at the files Wiki.swift and Page.swift.

Combine is Apple’s framework for handling asynchronous events in Swift. Combine and SwiftUI are the future for making iOS and Mac apps. This post lists resources for learning Combine.

Books

• Joseph Heck’s Using Combine is freely available online.
• Daniel Steinberg’s A Combine Kickstart provides a nice introduction to Combine.
• Donny Wals’s Practical Combine provides many practical examples of using Combine.
• Ray Wenderlich’s Combine: Asynchronous Programming with Combine is a comprehensive resource for Combine.
• Mark Moeykens’ Combine Mastery in SwiftUI provides a visual guide to learning Combine with SwiftUI.

Websites

I don’t know of any websites focused solely on Combine, but the following websites have articles on Combine:

• Antoine van der Lee
• Donny Wals
• John Sundell

A common scenario for iOS and Mac apps is to save data when someone quits the app. You have written a function to save the data. Where do you make the call when the app quits? This article answers that question, both for the SwiftUI app life cycle and the classic AppDelegate life cycle.

Using the SwiftUI App Life Cycle

In Xcode 12 Apple introduced a native SwiftUI app life cycle. The new life cycle has a scenePhase environment value that stores the app’s current phase, such as active, inactive, or background.

Add a property to the app struct for the scene phase. Add the .onChange modifier to the app’s window group or document group. Check if the phase is .background. If it is, make a call to save the data. The following code shows how to check when the app goes in the background:

Using the AppDelegate Life Cycle

If your Xcode project has a file named AppDelegate.swift, it is using the AppDelegate life cycle. Open the AppDelegate.swift function, and you should see multiple empty functions for handling app events.

An iOS app that wants to save when someone quits the app should make a call to save the data in the function applicationDidEnterBackground. This function is called when the person quits your app.

A Mac app should make the save call in applicationWillTerminate.