Android Tutorial

We can write kotlin programs in text editor and run the programs using command line. We need kotlin complier for this . we can download KOTLIN COMPILER FROM HERE  .  1. Download kotlin-compiler -1.3.72.z.ip 2. Unzip Kotlin compiler to program files in c drive           3. Copy the path of bin (C:\Program Files\kotlin\bin) and add it your to PATH in System variable.    If you do not know how to add path in system variable , you can use the following link Adding PATH in System variable 4. Now open notepad and write your kotlin program fun main(args: Array<String>) { println("Hello World") } 5. save the program as helloworld.kt , i have saved it to my Documents 6. Open cmd  7. I have saved my helloworld.kt file in Documents folder , so i am changing my directory to Documents  (you have to change it to your directory where the file is saved)                 cd documents 8. Compile the kotlin program using the following command                 kotlinc helloword.kt -inc

when user navigates in an application android maintains back stack of destinations . This allows android to go back to previous destination when user clicks back button . some  times we  need to implement our own back button behavior  for best user experience . For example  if we are in a timer based quiz  application . when the user clicks on the back button if we go back to the previous destination without stopping  the counter , it will crash  the application . So first we need to know whether the  user  pressed the back button accidentally or not by  using a dialogue box . If the user want to go back to previous destination  we need to stop the counter and  then go back to the previous destination. We can control the back button hahavior byusing OnBackPressedDispatcher  . This controls how back button events are dispatched to one or more onBackPressedCallback objects . callbacks are added using addCallback methods. exampe code is given below val callback = requireActivity().onBa

If you are using navigation UI in your application , if you want to hide your app bar (top bar of your app showing navigation icon)  or back navigation arrow in a particular fragment you can do like this in your Mainactivity class MainActivity : AppCompatActivity() { class MainActivity : AppCompatActivity() { private lateinit var drawerlayout : DrawerLayout private lateinit var navView : NavigationView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) drawerlayout = findViewById(R.id.drawer_layout) navView = findViewById(R.id.nav_view) val navController : NavController = this.findNavController(R.id.navhost) NavigationUI.setupActionBarWithNavController(this,navController,drawerlayout) NavigationUI.setupWithNavController(navView,navController) navController.addOnDestinationChangedListener { _, destination, _ -> if(desti