fragment_discover.xml

<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"
    android:background="?attr/colorPrimary"
    tools:context="com.mobymagic.shazamclone.discover.DiscoverFragment">

    <!-- The left and right constraint on the parent centers the view horizontally while the top
     and bottom constraints centers it vertically. This is because when you set the left,
     right or top, bottom constraints bigger than the view it self, the view gets centered
     between the two constraints i.e the bias is set to 50%. -->
    
    <com.github.ybq.android.spinkit.SpinKitView
        android:id="@+id/discoverProgressView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="parent"
        style="@style/SpinKitView.MultiplePulse" />

    <ImageButton
        android:id="@+id/discoverStartStopButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="24dp"
        android:background="@drawable/bg_circle_white"
        android:contentDescription="@string/discover_action_content_desc_start_identifying"
        android:src="@drawable/ic_mic_black_48dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="parent" />

    <!-- The left and right constraint on the parent centers the view horizontally while the
     bottom constraint keeps the bottom of the view with the bottom of the parent (Align to bottom) -->
    
    <TextView
        android:id="@+id/discoverHintTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="16dp"
        android:textAppearance="@style/TextAppearance.AppCompat.Title"
        android:textColor="@color/primary_text_light"
        android:text="@string/discover_hint_tap_to_identify"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />
    
</android.support.constraint.ConstraintLayout>