请问Android :drawable 可以用xml赋值吗？

当然可以了，比如，下面是一个带圆角的按钮的三种状态

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

    <item android:state_pressed="false">

        <shape>
             <solid
                android:color="@color/white"
              />                 
            <!-- 描边 -->
             <stroke
                android:width="2px"
                android:color="@color/font_22a7f0" 
                />  
               <corners 
               android:radius="5dp" 
                />  
        </shape>        

    </item> 
    <item android:state_pressed="true">

        <shape>
             <solid
                android:color="@color/gray2"
              />                     
            <!-- 描边 -->
             <stroke
                android:width="2px"
                android:color="@color/font_22a7f0" 
                />  
               <corners 
               android:radius="5dp" 
                />  
        </shape>            

    </item>     

</selector>