Cannot use databinding with bt_title

[socmia]

I want to use databinding with bt_title.
How can i do it?

<com.gauravk.bubblenavigation.BubbleToggleView
                android:id="@+id/l_item_home"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                app:bt_active="true"
                app:bt_colorActive="@color/red_active"
                app:bt_colorInactive="@color/red_inactive"
                app:bt_icon="@drawable/ic_home"
                app:bt_shape="@drawable/transition_background_drawable_home"
                app:bt_title="@{String.valueOf(viewmodel.currentNumber)}" />