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android kotlin - WebView example

MainActivity.kt

package com.cfsuman.kotlintutorials

import android.app.Activity
import android.content.Context
import android.graphics.Bitmap
import android.os.Build
import android.os.Bundle
import android.view.View
import android.webkit.WebChromeClient
import android.webkit.WebSettings
import android.webkit.WebView
import android.webkit.WebViewClient
import android.widget.Button
import android.widget.ProgressBar
import android.widget.Toast
import androidx.appcompat.app.AlertDialog


class MainActivity : Activity() {
    lateinit var webView:WebView
    private val url = "https://www.android--code.com"

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


        // Get the widgets references from XML layout
        webView = findViewById(R.id.webView)
        val buttonLoad: Button = findViewById(R.id.buttonLoad)
        val buttonBack: Button = findViewById(R.id.buttonBack)
        val buttonForward: Button = findViewById(R.id.buttonForward)
        val progressBar: ProgressBar = findViewById(R.id.progressBar)


        // Get the web view settings instance
        val settings = webView.settings

        // Enable java script in web view
        settings.javaScriptEnabled = true


        // Enable and setup web view cache
        //settings.setAppCacheEnabled(true)
        settings.cacheMode = WebSettings.LOAD_DEFAULT
        //settings.setAppCachePath(cacheDir.path)


        // Enable zooming in web view
        settings.setSupportZoom(true)
        settings.builtInZoomControls = true
        settings.displayZoomControls = true


        // Zoom web view text
        settings.textZoom = 110


        // Enable disable images in web view
        settings.blockNetworkImage = false
        // Whether the WebView should load image resources
        settings.loadsImagesAutomatically = true


        // More web view settings
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            settings.safeBrowsingEnabled = true  // api 26
        }
        //settings.pluginState = WebSettings.PluginState.ON
        settings.useWideViewPort = true
        settings.loadWithOverviewMode = true
        settings.javaScriptCanOpenWindowsAutomatically = true
        settings.mediaPlaybackRequiresUserGesture = false


        // More optional settings, you can enable it by yourself
        settings.domStorageEnabled = true
        settings.setSupportMultipleWindows(true)
        settings.loadWithOverviewMode = true
        settings.allowContentAccess = true
        settings.setGeolocationEnabled(true)
        settings.allowUniversalAccessFromFileURLs = true
        settings.allowFileAccess = true

        // WebView settings
        webView.fitsSystemWindows = true


        // Activate hardware acceleration
        webView.setLayerType(View.LAYER_TYPE_HARDWARE, null)


        // Set web view client
        webView.webViewClient = object: WebViewClient(){
            override fun onPageStarted(view: WebView, url: String,
                                       favicon: Bitmap?) {
                // Page loading started
                // Do something
                toast("Page loading.")

                // Enable disable back forward button
                buttonBack.isEnabled = webView.canGoBack()
                buttonForward.isEnabled = webView.canGoForward()
            }

            override fun onPageFinished(view: WebView, url: String) {
                // Page loading finished
                // Display the loaded page title in a toast message
                toast("Page loaded: ${view.title}")

                // Enable disable back forward button
                buttonBack.isEnabled = webView.canGoBack()
                buttonForward.isEnabled = webView.canGoForward()
            }
        }


        // Set web view chrome client
        webView.webChromeClient = object: WebChromeClient(){
            override fun onProgressChanged(
                view: WebView, newProgress: Int) {
                progressBar.progress = newProgress
            }
        }


        // Load button click listener
        buttonLoad.setOnClickListener{
            // Load url in a web view
            webView.loadUrl(url)
        }


        // Back button click listener
        buttonBack.setOnClickListener{
            if(webView.canGoBack()){
                // Go to back history
                webView.goBack()
            }
        }


        // Forward button click listener
        buttonForward.setOnClickListener{
            if(webView.canGoForward()){
                // Go to forward history
                webView.goForward()
            }
        }
    }



    // Method to show app exit dialog
    private fun showAppExitDialog() {
        val builder = AlertDialog.Builder(this)

        builder.setTitle("Please confirm")
        builder.setMessage("No back history found," +
                " want to exit the app?")
        builder.setCancelable(true)

        builder.setPositiveButton("Yes") { _, _ ->
            // Do something when user want to exit the app
            // Let allow the system to handle
            // the event, such as exit the app
            super@MainActivity.onBackPressed()
        }

        builder.setNegativeButton("No") { _, _ ->
            // Do something when want to stay in the app
            toast("thank you.")
        }

        // Create the alert dialog using alert dialog builder
        val dialog = builder.create()

        // Finally, display the dialog when user press back button
        dialog.show()
    }



    // Handle back button press in web view
    override fun onBackPressed() {
        if (webView.canGoBack()) {
            // If web view have back history,
            // then go to the web view back history
            webView.goBack()
            toast("Going to back history")
        } else {
            // Ask the user to exit the app or stay in here
            showAppExitDialog()
        }
    }
}



// Extension function to show toast message
fun Context.toast(message: String) {
    Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
}
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/rootLayout"
    android:background="#DCDCDC">

    <ProgressBar
        android:id="@+id/progressBar"
        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
        android:layout_width="match_parent"
        android:layout_height="2dp"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/buttonLoad"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Load URL"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/progressBar" />

    <Button
        android:id="@+id/buttonBack"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Back"
        app:layout_constraintBottom_toBottomOf="@+id/buttonLoad"
        app:layout_constraintStart_toEndOf="@+id/buttonLoad" />

    <Button
        android:id="@+id/buttonForward"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:text="Forward"
        app:layout_constraintBottom_toBottomOf="@+id/buttonBack"
        app:layout_constraintStart_toEndOf="@+id/buttonBack" />

    <WebView
        android:id="@+id/webView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/buttonLoad" />

</androidx.constraintlayout.widget.ConstraintLayout>
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