onclick_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools">
    <data>           
        <variable
            name="presenter"
            type="com.example.MyPresenter"/>
            
        <variable
            name="model"
            type="com.example.MyModel"/>
    </data>

    <android.support.design.widget.CoordinatorLayout
        android:id="@+id/activity_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
                <android.support.design.widget.TextInputEditText
                    android:layout_width="match_parent"
                    android:layout_height="80dp"
                    android:hint="@string/username"
                    android:text="@={model.username}"
                    android:maxLines="1"/>
                  <android.support.design.widget.FloatingActionButton
                        android:id="@+id/fab"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="bottom|end"
                        android:layout_margin="@dimen/fab_margin"
                        android:onClick="@{()-> presenter.makeServerCall(model)}"
                        app:srcCompat="@android:drawable/ic_menu_send"/>
    </android.support.design.widget.CoordinatorLayout>
</layout>