sheishuoAPP/uikit/res/drawable/nim_message_button_bottom_add_selector.xml

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

    <item android:state_pressed="true" android:drawable="@drawable/nim_message_input_plus_pressed" />
    <item android:state_focused="true" android:drawable="@drawable/nim_message_input_plus_pressed" />
    <item android:drawable="@drawable/nim_message_input_plus" />
</selector>