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      activity_main.xml
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<?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">

    <TimePicker
        android:id="@+id/timePicker"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="71dp"
        android:timePickerMode="spinner"
        app:layout_constraintBottom_toTopOf="@+id/datePicker" />


    <DatePicker
        android:id="@+id/datePicker"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="71dp"
        android:datePickerMode="spinner"
        app:layout_constraintTop_toBottomOf="@+id/timePicker"
        tools:layout_editor_absoluteX="41dp" />

</androidx.constraintlayout.widget.ConstraintLayout>