Argument Type does not conform to expected type 'WKScriptMessageHandler'

Question

I'm trying two-way integration between Swift and Javascript interfacing with SwiftUI.
Here is interfacing WebKit with SwiftUI.

import SwiftUI
import WebKit

struct ggWebView : UIViewRepresentable {

    let filePath: String

    func makeUIView(context: Context) -> WKWebView  {
        return WKWebView()
    }

    func updateUIView(_ uiView: WKWebView, context: Context) {
        uiView.configuration.userContentController.add(self, name: "jsHandler")
        let bundleURL = Bundle.main.resourceURL!.absoluteURL
        let html = bundleURL.appendingPathComponent(filePath)
        uiView.loadFileURL(html, allowingReadAccessTo:bundleURL)
    }

    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        if message.name == "jsHandler"{
            print(message.body)
        }
    }
}

userContentController.add(self, name: "jsHandler") shows an error at self with Argument type 'ggWebView' does not conform to expected type 'WKScriptMessageHandler'.

Maciej Gad · Accepted Answer · 2019-11-15T17:18:21.550

8

As WKScriptMessageHandler require that object that implements it inherit from NSObject it is better to create a separate class ContentController that will be implementing those protocol, rather than changing the type of GgWebView.

import SwiftUI
import WebKit

struct GgWebView: UIViewRepresentable {

    let filePath: String
    let contentController = ContentController()

    func makeUIView(context: Context) -> WKWebView  {
        return WKWebView()
    }

    func updateUIView(_ uiView: WKWebView, context: Context) {
        uiView.configuration.userContentController.add(contentController, name: "jsHandler")
        let bundleURL = Bundle.main.resourceURL!.absoluteURL
        let html = bundleURL.appendingPathComponent(filePath)
        uiView.loadFileURL(html, allowingReadAccessTo:bundleURL)
    }

    class ContentController: NSObject, WKScriptMessageHandler {
        func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
            if message.name == "jsHandler"{
                print(message.body)
            }
        }
    }
}

You have to confirm ggWebView (BTW this is not the best name for a class because it should start with capital letter) to WKScriptMessageHandler protocol and implement func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) method. You have to change the type of ggWebView from structure to class. I can see that you already add a userContentController(_:didReceive:) method, so you only need to update your class signature to:

class ggWebView: UIViewRepresentable, WKScriptMessageHandler {

edited Nov 15 '19 at 17:18

answered Nov 15 '19 at 14:21

Maciej Gad

1,701
16
21

Got two error: `Non-class type 'ggWebView' cannot conform to class protocol 'WKScriptMessageHandler` and `Non-class type 'ggWebView' cannot conform to class protocol 'NSObjectProtocol'` – Lonaso Nov 15 '19 at 14:46
@Lonaso try changing from `structure` to `class` – Maciej Gad Nov 15 '19 at 15:13
You will need also to provide `init` like: `init(filePath: String) { self.filePath = filePath }` – Maciej Gad Nov 15 '19 at 15:15
Can you please full working example, please? I got 4 more errors after doing that. @bazyl87 – Lonaso Nov 15 '19 at 15:56
@Lonaso I've updated the answer, please let me know if it working for you – Maciej Gad Nov 15 '19 at 17:18
1

Question: How would I be able to change a @State property of GgWebView from inside the contentController instance? – TD540 Apr 16 '21 at 23:02
1

just use Maciej's implementation, it works – MartianMartian Jan 14 '22 at 13:03

Argument Type does not conform to expected type 'WKScriptMessageHandler'

1 Answers1