WebView interaction with Html

MainActivity.java

package com.habaco.test.js2webview

import android.os.Build
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.webkit.JavascriptInterface
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // 讀取本地網頁
        webView?.loadUrl("file:///android_asset/testJS.html")

        // 允許 js
        webView?.settings?.javaScriptEnabled = true

        // 注入 js interface，js-object = android_app
        webView?.addJavascriptInterface(JavaInterface(), "android_app")

        button?.setOnClickListener {
            val javascript = "javascript:mobileCallJs('${input?.text.toString()}')"
            Log.i(">>>", "javascript --> $javascript")

            // 版本判斷使用 javascript
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
                webView.evaluateJavascript(javascript, null)
            } else {
                webView.loadUrl(javascript)
            }
        }
    }

    inner class JavaInterface {

        // 標記 javascript function
        @JavascriptInterface
        fun callAndroid(value: String) {
            Toast.makeText(this@MainActivity, value, Toast.LENGTH_SHORT).show()
        }
    }
}