init

app/src/main/res/layout-land/activity_main.xml

@@ -0,0 +1,29 @@
+<?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"
+    tools:context="com.mjsheng.myappstore.MainActivity">
+
+    <Button
+        android:id="@+id/btn_babySystem"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="babySystem" />
+
+    <Button
+        android:id="@+id/btn_primarySystem"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="primarySystem"
+        app:layout_constraintTop_toBottomOf="@+id/btn_babySystem" />
+
+    <Button
+        android:id="@+id/btn_middleSystem"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="middleSystem"
+        app:layout_constraintTop_toBottomOf="@id/btn_primarySystem" />
+
+</android.support.constraint.ConstraintLayout>