yinmeng-android/nim_uikit/res/layout/nim_custom_popup_window.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:orientation="vertical">

    <LinearLayout
        android:id="@+id/ll_root"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/nim_shape_767676_8dp"
        android:orientation="vertical">

    </LinearLayout>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_height="wrap_content"
        android:src="@drawable/nim_bottom_arrow" />

</LinearLayout>