如何知道fab按钮在项目中的使用位置(活动、片段和xml)？

<!-- res/layout/activity_main.xml -->
<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="16dp"
    app:srcCompat="@android:drawable/ic_dialog_email" />

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val fab: FloatingActionButton = findViewById(R.id.fab)
        fab.setOnClickListener { view ->
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show()
        }
    }
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    Log.d("FAB_LOCATION", "Activity: MainActivity")
    val fab: FloatingActionButton = findViewById(R.id.fab)
    fab.setOnClickListener {
        Log.d("FAB_CLICKED", "FAB clicked in MainActivity")
    }
}