android webView側のinput type="file"でファイルアップロードをkotlinで実装したい

package jp.hogehoge.test

import android.content.ActivityNotFoundException
import android.content.Intent
import android.net.Uri
import android.os.Build
import android.os.Bundle
import android.util.Log
import android.webkit.*
import android.widget.Button
import android.widget.Toast
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity

private var mUploadMessage: ValueCallback<Uri>? = null

var uploadMessage:ValueCallback<Array<Uri>>? = null

val REQUEST_SELECT_FILE = 100
val FILECHOOSER_RESULTCODE = 1

class WebSite : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_web_site)

        val myWebView: WebView = findViewById(R.id.webSiteView)
        myWebView?.webChromeClient = object:WebChromeClient() {

            override fun onJsAlert(view: WebView, url: String, message: String, result: JsResult): Boolean {
                Log.d("alert", message)
                val dialogBuilder = AlertDialog.Builder(this@WebSite)

                dialogBuilder.setMessage(message)
                    .setCancelable(false)
                    .setPositiveButton("OK") { _, _ ->
                        result.confirm()
                    }

                val alert = dialogBuilder.create()
                alert.show()

                return true
            }

            // For 3.0+ Devices (Start)
            // onActivityResult attached before constructor
            fun openFileChooser(uploadMsg : ValueCallback<Uri>, acceptType:String) {
                mUploadMessage = uploadMsg
                val i = Intent(Intent.ACTION_GET_CONTENT)
                i.addCategory(Intent.CATEGORY_OPENABLE)
                i.type = "image/jpeg"
                startActivityForResult(Intent.createChooser(i, "File Browser"), FILECHOOSER_RESULTCODE)
            }

            // For Lollipop 5.0+ Devices
            override fun onShowFileChooser(mWebView:WebView, filePathCallback:ValueCallback<Array<Uri>>, fileChooserParams:WebChromeClient.FileChooserParams):Boolean {
                if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP){
                    if (uploadMessage != null) {
                        uploadMessage?.onReceiveValue(null)
                        uploadMessage = null
                    }
                    uploadMessage = filePathCallback
                    val intent = fileChooserParams.createIntent()
                    try {
                        startActivityForResult(intent, REQUEST_SELECT_FILE)
                    } catch (e: ActivityNotFoundException) {
                        uploadMessage = null
                        Toast.makeText(getApplicationContext(), "Cannot Open File Chooser", Toast.LENGTH_LONG).show()
                        return false
                    }
                    return true
                }else{
                    return false
                }
            }

            //For Android 4.1 only
            fun openFileChooser(uploadMsg:ValueCallback<Uri>, acceptType:String, capture:String) {
                mUploadMessage = uploadMsg
                val intent = Intent(Intent.ACTION_GET_CONTENT)
                intent.addCategory(Intent.CATEGORY_OPENABLE)
                intent.type = "image/jpeg"
                startActivityForResult(Intent.createChooser(intent, "File Browser"), FILECHOOSER_RESULTCODE)
            }

            fun openFileChooser(uploadMsg:ValueCallback<Uri>) {
                //filePermission()
                mUploadMessage = uploadMsg
                val i = Intent(Intent.ACTION_GET_CONTENT)
                i.addCategory(Intent.CATEGORY_OPENABLE)
                i.type = "image/jpeg"
                startActivityForResult(Intent.createChooser(i, "File Browser"), FILECHOOSER_RESULTCODE)
            }
        }

        // これがないとwebView内でなくブラウザが起動してしまう
        myWebView.setWebViewClient(object : WebViewClient() {
            override fun shouldOverrideUrlLoading(view: WebView?, request: WebResourceRequest?): Boolean {
                return false
            }
        })

        myWebView.loadUrl("https://hogehoge.jp/login")
        myWebView.settings.javaScriptEnabled = true

        val goBackMainButton = findViewById(R.id.goBackMainBtn) as Button
        goBackMainButton.setOnClickListener {
            finish()
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            if (requestCode == REQUEST_SELECT_FILE) {
                if (uploadMessage != null) {
                    uploadMessage?.onReceiveValue(
                        WebChromeClient.FileChooserParams.parseResult(
                            resultCode,
                            data
                        )
                    )
                    uploadMessage = null
                }
            }
        } else if (requestCode == FILECHOOSER_RESULTCODE) {
            if (mUploadMessage != null) {
                var result = data?.data
                mUploadMessage?.onReceiveValue(result)
                mUploadMessage = null
            }
        } else {
            Toast.makeText(
                this,
                "Failed to open file uploader, please check app permissions.",
                Toast.LENGTH_LONG
            ).show()
            super.onActivityResult(requestCode, resultCode, data)
        }
    }
}