activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/sync"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="621dp"
        android:layout_marginBottom="62dp"
        android:text="Sync"
        android:textAlignment="center"
        android:textColorHighlight="#3F51B5"
        android:textColorLink="#344BC8"
        app:iconTint="#883B3B"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="595dp"
        android:layout_marginBottom="7dp"
        android:text="Sync Your Sonic Gauge to Application"
        android:textAlignment="center"
        app:layout_constraintBottom_toTopOf="@+id/sync"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="29dp"
        android:layout_marginBottom="491dp"
        android:fontFamily="monospace"
        android:text="Sonic Gauge"
        android:textAppearance="@style/TextAppearance.AppCompat.Display2"
        android:textStyle="bold"
        android:typeface="sans"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ListView
        android:id="@+id/listview"
        android:layout_width="285dp"
        android:layout_height="359dp"
        android:layout_marginTop="78dp"
        android:layout_marginBottom="62dp"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

    <TextView
        android:id="@+id/ListTxt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="41dp"
        android:text="Available Devices"
        app:layout_constraintBottom_toTopOf="@+id/listview"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2"
        app:layout_constraintVertical_bias="1.0" />

    <ImageView
        android:id="@+id/search_bt"
        android:layout_width="33dp"
        android:layout_height="32dp"
        android:layout_marginTop="12dp"
        android:layout_marginBottom="12dp"
        app:layout_constraintBottom_toTopOf="@+id/ListTxt"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2"
        app:srcCompat="@mipmap/ble" />
</androidx.constraintlayout.widget.ConstraintLayout>