How to detect click on HTML button through javascript in Android WebView?

This example demonstrate about How to lock the Android device programmatically.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml
<? xml version= "1.0" encoding= "utf-8" ?>
<RelativeLayout xmlns: android = "http://schemas.android.com/apk/res/android"
   xmlns: tools = "http://schemas.android.com/tools"
   android :layout_width= "match_parent"
   android :layout_height= "match_parent"
   android :layout_margin= "16dp"
   tools :context= ".MainActivity" >
   <Button
      android :onClick= "loadPage"
      android :layout_width= "match_parent"
      android :layout_height= "wrap_content"
      android :text= "Load web Page" />
</RelativeLayout>
Step 3 − Add the following code to assets/page.html
<html>
   <body>
      First name: <input type= "text" name= "fname" id= "txtfname" ><br>
      Last name: <input type= "text" name= "lname" id= "txtlname" ><br>
      <script>
         function getValues() {
            document.getElementById("btnOK").value =
            document.getElementById("txtfname").value+"
            "+document.getElementById("txtlname").value;
         }
      </script>
      <button type= "button" value= "" id= "btnOK" onclick= " getValues();ok.performClick(this.value); " > OK </button>
   </body>
</html>
Step 4 − Add the following code to src/MainActivity
package app.tutorialspoint.com.sample ;
import android.os.Bundle ;
import android.support.v7.app.AppCompatActivity ;
import android.view.View ;
import android.webkit. JavascriptInterface ;
import android.webkit.WebSettings ;
import android.webkit.WebView ;
import android.widget.Toast ;
public class MainActivity extends AppCompatActivity {
   @Override
   protected void onCreate (Bundle savedInstanceState) {
      super .onCreate(savedInstanceState) ;
      setContentView(R.layout. activity_main ) ;
   }
   public void loadPage (View view) {
      WebView browser = new WebView( this ) ;
      browser.getSettings().setJavaScriptEnabled( true ) ;
      browser.loadUrl( "file:///android_asset/page.html" ) ;
      setContentView(browser) ;
      WebSettings ws = browser.getSettings() ;
      ws.setJavaScriptEnabled( true ) ;
      browser.addJavascriptInterface( new Object() {
         @JavascriptInterface // For API 17+
         public void performClick (String strl) {
            Toast. makeText (MainActivity. this, strl , Toast. LENGTH_SHORT ).show() ;
         }
      } , "ok" ) ;
   }
}
Step 5 − Add the following code to androidManifest.xml
<? xml version= "1.0" encoding= "utf-8" ?>
<manifest xmlns: android = "http://schemas.android.com/apk/res/android"
   package= "app.tutorialspoint.com.sample" >
   <uses-permission android :name= "android.permission.CALL_PHONE" />
   <application
      android :allowBackup= "true"
      android :icon= "@mipmap/ic_launcher"
      android :label= "@string/app_name"
      android :roundIcon= "@mipmap/ic_launcher_round"
      android :supportsRtl= "true"
      android :theme= "@style/AppTheme" >
      <activity android :name= ".MainActivity" >
         <intent-filter>
            <action android :name= "android.intent.action.MAIN" />
            <category android :name= "android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
      <receiver
         android :name= ".DeviceAdmin"
         android :description= "@string/app_description"
         android :label= "@string/app_name"
         android :permission= "android.permission.BIND_DEVICE_ADMIN" >
         <meta-data
            android :name= "android.app.device_admin"
            android :resource= "@xml/policies" />
         <intent-filter>
            <action android :name= "android.app.action.DEVICE_ADMIN_ENABLED" />
         </intent-filter>
      </receiver>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –