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 <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/button_1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_1"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@ id/button_2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent />
    
</androidx.constraintlayout.widget.ConstraintLayout>
  

Вы можете использовать:

   <Button
    android:id="@ id/button_3"
    android:text="button_3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintBottom_toBottomOf="parent" />

  <Button
    android:id="@ id/button_4"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="button_4"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintBottom_toBottomOf="parent" />