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
var html: String
webView.loadHTMLString(html, baseURL: nil)
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.
var bookURL: URL
var currentChapterFilename: String
let oebpsFolder = bookURL.appendingPathComponent("OEBPS")
let textFolder = oebpsFolder.appendingPathComponent("Text")
let chapterFile = textFolder.appendingPathComponent(currentChapterFilename)
webView.loadFileURL(chapterFile, allowingReadAccessTo: oebpsFolder)