@JavascriptInterface に解析用メソッド呼び出しを追加

MainFragment.kt

package com.example.webscrapingtest.view

import androidx.lifecycle.ViewModelProvider
import android.os.Bundle
import android.util.Log
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.webkit.JavascriptInterface
import android.webkit.WebView
import android.webkit.WebViewClient
import androidx.databinding.DataBindingUtil
import com.example.webscrapingtest.R
import com.example.webscrapingtest.databinding.MainFragmentBinding
import com.example.webscrapingtest.viewmodel.MainViewModel
import kotlinx.android.synthetic.main.main_fragment.view.*

class MainFragment : Fragment() {

    private lateinit var webViewModel: MainViewModel
    private lateinit var binding: MainFragmentBinding

    companion object {
        fun newInstance() = MainFragment()
    }

    private lateinit var viewModel: MainViewModel

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        binding = DataBindingUtil.inflate(inflater, R.layout.main_fragment, container, false)
        binding.setLifecycleOwner(this)

        val view = binding.root
        view.webView.settings.javaScriptEnabled = true
        // 規定のブラウザではなく、WebViewで表示するためコード
        view.webView.webViewClient = object : ViewSourceClient(){}
        view.webView.addJavascriptInterface(this, "fragment")
        view.webView.loadUrl("https://yahoo.co.jp/")

        return binding.getRoot()
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProvider(this).get(MainViewModel::class.java)
    }

    open class ViewSourceClient : WebViewClient() {
        override fun onPageFinished(view: WebView, url: String) {
            view.loadUrl("javascript:window.fragment.viewSource(document.getElementsByTagName('html')[0].outerHTML);")
        }
    }

    @JavascriptInterface
    fun viewSource(src: String) {
        // 追加
        viewModel.analyzeHtml(src)
    }
}