安卓: ConstraintLayout布局4个按钮，分成2组，分布不均

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 1"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/button2"
        app:layout_constraintHorizontal_chainStyle="packed"
        app:layout_constraintHorizontal_bias="0.2"
        app:layout_constraintHorizontal_margin="8dp"
        app:layout_constraintVertical_bias="0.2"
        app:layout_constraintVertical_margin="8dp"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 2"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/button1"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintHorizontal_chainStyle="packed"
        app:layout_constraintHorizontal_bias="0.8"
        app:layout_constraintHorizontal_margin="8dp"
        app:layout_constraintVertical_bias="0.2"
        app:layout_constraintVertical_margin="8dp"/>

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 3"
        app:layout_constraintTop_toBottomOf="@+id/button1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/button4"
        app:layout_constraintHorizontal_chainStyle="packed"
        app:layout_constraintHorizontal_bias="0.2"
        app:layout_constraintHorizontal_margin="16dp"
        app:layout_constraintVertical_bias="0.8"
        app:layout_constraintVertical_margin="8dp"/>

    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 4"
        app:layout_constraintTop_toBottomOf="@+id/button2"
        app:layout_constraintLeft_toRightOf="@+id/button3"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintHorizontal_chainStyle="packed"
        app:layout_constraintHorizontal_bias="0.8"
        app:layout_constraintHorizontal_margin="16dp"
        app:layout_constraintVertical_bias="0.8"
        app:layout_constraintVertical_margin="8dp"/>

</androidx.constraintlayout.widget.ConstraintLayout>