android的xml文件中@和?的用法

a reference to another resource, in the form "@[+][package:]type:name"

 

 to a theme attribute in the form "?[package:][type:]name"

  例：

 

<TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text1" android:layout_width="wrap_content" android:layout_height="24sp" android:singleLine="true" style="?android:attr/spinnerDropDownItemStyle" />