I'm trying to create view with button and fragemtn with list under this button. The problem is that the list starts from top of button not from bottom and it's look like this: 

[![enter image description here](https://i.stack.imgur.com/lbB94.png)](https://i.stack.imgur.com/lbB94.png)

Layout code:

```
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".activities.BluetoothActivity">

    <Button
            android:text="@string/scan"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/BluetoothScanButton"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="8dp"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="8dp"
            android:layout_marginTop="40dp"
            app:layout_constraintTop_toTopOf="parent"/>

    <fragment
            android:id="@+id/BluetoothDevicesFragment"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:name="com.tatara.taffico.DeviceListFragment"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="8dp"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="8dp"
            app:layout_constraintBottom_toBottomOf="parent"
            android:layout_marginTop="8dp"
            app:layout_constraintTop_toBottomOf="@+id/BluetoothScanButton"/>
</android.support.constraint.ConstraintLayout>

```

Could anyone help me to fix it ?