为什么imageview不会竖向排列
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
<ImageView
android:id="@+id/imageView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:src="@drawable/ic_launcher" />
<ImageView
android:id="@+id/imageView2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@drawable/ic_launcher" />
<ImageView
android:id="@+id/imageView3"
android:layout_width="match_parent"
android:layout_height="20dp"
android:background="#f0f0f0" />
</RelativeLayout>