Android ConstraintLayout约束布局的居中

xml代码：<?xml  version="1.0" encoding="utf-8"?>

xmlns:app="http://schemas.android.com/apk/res-auto"

android:layout_width="match_parent"

android:layout_height="match_parent">

android:id="@+id/text1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:background="@android:color/holo_red_light"

android:text="text1：顶部水平居中"

android:textColor="@android:color/white"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

android:id="@+id/text2"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:background="@android:color/holo_red_light"

android:text="text2：位于text1下且水平居中"

android:textColor="@android:color/white"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toBottomOf="@id/text1" />

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:background="@android:color/holo_green_light"

android:text="水平居中，且居于text2下"

android:textColor="@android:color/white"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toBottomOf="@id/text2" />

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:background="@android:color/holo_red_light"

android:text="居中位于底部"

android:textColor="@android:color/white"

app:layout_constraintBottom_toBottomOf="parent"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintStart_toStartOf="parent" />

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:background="@android:color/holo_blue_bright"

android:text="全局居中"

android:textColor="@android:color/white"

app:layout_constraintBottom_toBottomOf="parent"

app:layout_constraintEnd_toEndOf="parent"

app:layout_constraintStart_toStartOf="parent"

app:layout_constraintTop_toTopOf="parent" />

输出结果如图：