Android 设置checkbox形状变化

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

    <item android:state_checked="true">
        <layer-list>
            <item>
                <shape android:shape="oval">
                    <size android:width="18dp" android:height="18dp" />
                    <stroke android:width="1dp" android:color="#B344FF" />
                    <solid android:color="#B344FF" />
                </shape>
            </item>
            <item android:drawable="@mipmap/ic_checked_1" />
        </layer-list>
    </item>
    <item>
        <shape android:shape="oval">
            <size android:width="18dp" android:height="18dp" />
            <stroke android:width="1dp" android:color="#B344FF" />
            <solid android:color="#FFFFFF" />
        </shape>
    </item>


</selector>