sheishuoAPP/uikit/res/drawable/nim_message_item_right_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@drawable/nim_message_right_blue_bg_pressed" android:state_pressed="true"/>
    <item android:drawable="@drawable/nim_message_right_blue_bg"/> <!-- default -->

</selector>