MainActivity.kt

package com.artemchep.webviewscroll

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.webkit.JavascriptInterface
import android.webkit.WebView
import android.webkit.WebViewClient
import kotlinx.android.synthetic.main.activity_main.*


class MainActivity : AppCompatActivity() {

    companion object {
        private const val JS_INTERFACE = "Android"
    }

    private val keyboardHeightPx by lazy {
        resources.getInteger(R.integer.keyboard_height_px)
    }

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

        webView.apply {
            settings.apply {
                javaScriptEnabled = true
            }

            addJavascriptInterface(JsInterface(this@MainActivity), JS_INTERFACE)
            webViewClient = object : WebViewClient() {
                override fun shouldOverrideUrlLoading(view: WebView, url: String): Boolean {
                    return false
                }

                override fun onPageFinished(view: WebView, url: String) {
                    super.onPageFinished(view, url)

                    evaluateJavascript("""
var eventHandler = function(event) {
    var type = event.target.nodeName.toLowerCase();
    if (type == 'input' || type == 'textarea') {
        var rect = event.target.getBoundingClientRect();
        var scrollY = $JS_INTERFACE.calculateVerticalScroll(rect.top + rect.height);

        if (scrollY > 0) {
            window.scrollBy(0, scrollY);
        }
    }
};
document.body.addEventListener('focus', eventHandler, true);
document.body.addEventListener('click', eventHandler, true);

// Add bottom margin to the page, so there's always a place
// to scroll
document.body.style.marginBottom="${keyboardHeightPx}px";
                    """, {})
                }
            }
        }

        loadSimple()
    }

    override fun onDestroy() {
        super.onDestroy()
        webView.removeJavascriptInterface(JS_INTERFACE)
    }

    private fun loadSimple() {
        webView.loadHtml("""
<div>
  <div style="margin-top: 600px">Title</div>
  <input type="text">
  <div>Footer</div>
</div>
    """)
    }

    private class JsInterface(private val activity: MainActivity) {

        @JavascriptInterface
        fun calculateVerticalScroll(y: Int): Int {
            val density = activity.resources.displayMetrics.density

            val windowHeightLimit = activity.window.decorView.height - activity.keyboardHeightPx * density
            val windowY = y * density + intArrayOf(0, 0)
                    .apply {
                        activity.webView.getLocationInWindow(this)
                    }[1]

            return Math.max((windowY - windowHeightLimit) / density, 0f).toInt()
        }

    }
    
}