Menus can be created either by using an XML resource file or by dynamically adding menu items through program code. This post is the latter.
To add a menu to an Activity, you need to override the onCreateOptionsMenu() function.
listing 1. onCreateOptionsMenu, excerpted from MainActivity
override fun onCreateOptionsMenu(menu: Menu?): Boolean Log.info("onCreateOptionsMenu") menu?.add("File") //this adds the menu item dynamically menu?.add("Exit") return super.onCreateOptionsMenu(menu) >
Note the use of safe-call operator(?.) in menu?.add, we need to use safe-call becasue the Menu object is declared as a nullable type in the function parameter (menu: Menu?)
Override the onOptionsItemSelected() function to handle the events when a menu item is clicked.
listing 2. onOptionsItemSelected, excerpted from MainActivity\
override fun onOptionsItemSelected(item: MenuItem?): Boolean when (item?.toString()) "File" -> Log.info("LOG File menu") > "Exit" -> Log.info("LOG Exit menu") > > return true >
We returned true from onOptionsItemSelected() becasue we don’t want any other listener to handle the event, returning true means we’ve already consumed the event, there is no more need for further handling.
listing 3. full program for MainActivity.Kt
package net.workingdev.oncreateoptionsmenulifecycle import android.support.v7.app.AppCompatActivity import android.os.Bundle import android.util.Log import android.view.Menu import android.view.MenuItem import android.widget.PopupMenu import kotlinx.android.synthetic.main.activity_main.* import java.util.logging.Logger class MainActivity : AppCompatActivity() val Log = Logger.getLogger(MainActivity::class.java.name) override fun onCreate(savedInstanceState: Bundle?) super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) > override fun onCreateOptionsMenu(menu: Menu?): Boolean Log.info("onCreateOptionsMenu") menu?.add("File") menu?.add("Exit") return super.onCreateOptionsMenu(menu) > override fun onOptionsItemSelected(item: MenuItem?): Boolean when (item?.toString()) "File" -> Log.info("LOG File menu") > "Exit" -> Log.info("LOG Exit menu") > > return true > >
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