menu_main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" tools:context=".MainActivity">
    <item
        android:id="@+id/share"
        android:title="@string/share"
        android:showAsAction="ifRoom"
        android:actionProviderClass="android.widget.ShareActionProvider"/>
    </menu>