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Rendering a petition: loadHTMLString

After all the JSON parsing, it's time for something easy: we need to create a detail view controller class so that it can draw the petition content in an attractive way.

The easiest way for rendering complex content from the web is nearly always to use a WKWebView, and we're going to use the same technique from project 4 to create DetailViewController that contains a web view.

Go to the File menu and choose New > File, then choose iOS > Source > Cocoa Touch Class. Click Next, name it “DetailViewController”, make it a subclass of “UIViewController”, then click Next and Create.

Replace all the DetailViewController code with this:

import UIKit
import WebKit

class DetailViewController: UIViewController {
    var webView: WKWebView!
    var detailItem: Petition?

    override func loadView() {
        webView = WKWebView()
        view = webView
    }

    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

This is almost identical to the code from project 4, but you'll notice I've added a detailItem property that will contain our dictionary of petition data.

That was the easy bit. The hard bit is that we can't just drop the petition text into the web view, because it will probably look tiny. Instead, we need to wrap it in some HTML, which is a whole other language with its own rules and its own complexities.

Now, this series isn't called "Hacking with HTML," so I don't intend to go into much detail here. However, I will say that the HTML we're going to use tells iOS that the page fits mobile devices, and that we want the font size to be 150% of the standard font size. All that HTML will be combined with the body value from our petition, then sent to the web view.

Place this in viewDidLoad(), directly beneath the call to super.viewDidLoad():

guard let detailItem = detailItem else { return }

let html = """
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style> body { font-size: 150%; } </style>
</head>
<body>
\(detailItem.body)
</body>
</html>
"""

webView.loadHTMLString(html, baseURL: nil)

There's a new Swift statement in there that is important: guard. This is used to create an "early return," which means you set your code up so that it exits immediately if critical data is missing. In our case, this unwraps detailItem into itself if it has a value, just like if let, but if it’s empty for some reason it will exit the method.

Note: It’s very common to unwrap variables using the same name, rather than create slight variations. In this case we could have used guard let unwrappedItem = detailItem, but that isn’t any clearer.

I've tried to make the HTML as clear as possible, but if you don't care for HTML don't worry about it. What matters is that there's a Swift string called html that contains everything needed to show the page, and that's passed in to the web view's loadHTMLString() method so that it gets loaded. This is different to the way we were loading HTML before, because we aren't using a website here, just some custom HTML.

That's it for the detail view controller, it really is that simple. However, we still need to connect it to the table view controller by implementing the didSelectRowAt method. Previously we used the instantiateViewController() method to load a view controller from Main.storyboard, but in this project DetailViewController isn’t in the storyboard – it’s just a free-floating class. This makes didSelectRowAt easier, because it can load the class directly rather than loading the user interface from a storyboard.

So, add this new method to your ViewController class now:

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let vc = DetailViewController()
    vc.detailItem = petitions[indexPath.row]
    navigationController?.pushViewController(vc, animated: true)
}

Go ahead and run the project now by pressing Cmd+R or clicking play, then tap on a row to see more detail about each petition. Some petitions don’t have detail text, but most do – try a few and see what you can find.

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