activity_blood_bank.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
    android:background="@drawable/bb"
    tools:context=".BloodBank">

    <!-- Label -->

    <TextView
        android:id="@+id/textView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="44dp"
        android:padding="8dip"
        android:text="@string/cityname"
        android:textColor="#FFFFFF"
        android:textSize="30sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <!-- Spinner Dropdown -->

    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="124dp"
        android:entries="@array/city"
        android:scrollbarSize="30dp"
        android:textColorHint="#FFFFFF"

        app:layout_constraintStart_toEndOf="@+id/textView"
        app:layout_constraintTop_toTopOf="parent" />

    <!-- Select Label -->

    <TextView
        android:id="@+id/textView2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="172dp"
        android:padding="8dip"
        android:text="@string/area"
        android:textSize="30sp"
        android:textColor="#FFFFFF"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <!-- Spinner Dropdown -->
    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:scrollbarSize="20dp"
        android:textColorHint="#FFFFFF"

        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

    <Button
        android:id="@+id/search"
        android:layout_width="110dp"
        android:layout_height="56dp"
        android:layout_marginStart="148dp"
        android:layout_marginLeft="148dp"
        android:layout_marginTop="160dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        android:background="#FFFFFF"
        android:fontFamily="@font/arial"
        android:text="@android:string/search_go"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/spinner2"
        app:layout_constraintVertical_bias="0.0" />

</android.support.constraint.ConstraintLayout>