[android] How to add Options Menu to Fragment in Android

TL;DR

Use the android.support.v7.widget.Toolbar and just do:

toolbar.inflateMenu(R.menu.my_menu)
toolbar.setOnMenuItemClickListener {
    onOptionsItemSelected(it)
}

Standalone Toolbar

Most of the suggested solutions like setHasOptionsMenu(true) are only working when the parent Activity has the Toolbar in its layout and declares it via setSupportActionBar(). Then the Fragments can participate in the menu population of this exact ActionBar:

Fragment.onCreateOptionsMenu(): Initialize the contents of the Fragment host's standard options menu.

If you want a standalone toolbar and menu for one specific Fragment you can to do the following:

menu_custom_fragment.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/menu_save"
        android:title="SAVE" />
</menu>

custom_fragment.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    ...

CustomFragment.kt

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val view = inflater.inflate(layout.custom_fragment, container, false)
    val toolbar = view.findViewById<Toolbar>(R.id.toolbar)
    toolbar.inflateMenu(R.menu.menu_custom_fragment)
    toolbar.setOnMenuItemClickListener {
        onOptionsItemSelected(it)
    }
    return view
}

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    return when (item.itemId) {
        R.id.menu_save -> {
            // TODO: User clicked the save button
            true
        }
        else -> super.onOptionsItemSelected(item)
    }
}

Yes, it's that easy. You don't even need to override onCreate() or onCreateOptionsMenu().

PS: This is only working with android.support.v4.app.Fragment and android.support.v7.widget.Toolbar (also be sure to use AppCompatActivity and an AppCompat theme in your styles.xml).