activity_main.xml

<?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.example.bwei.mylianxi.MainActivity">   <com.example.bwei.mylianxi.CustomView       android:id="@+id/mybanner"       android:layout_width="match_parent"       android:layout_height="200dp"       >   </com.example.bwei.mylianxi.CustomView></android.support.constraint.ConstraintLayout>