2019-09-05 通过layer-list实现输入框下划线

<?xml version="1.0" encoding="utf-8"?>
<layer-list
    xmlns:android="http://schemas.android.com/apk/res/android">
  <item
      android:left="-2dp"
      android:right="-2dp"
      android:top="-2dp"
      >
    <selector>
      <item android:state_focused="true">
        <shape>
          <stroke
              android:color="@color/red"
              android:width="1dp"
              />
        </shape>
      </item>
      <item>
        <shape>
          <stroke
              android:color="@color/white"
              android:width="1dp"
              />
        </shape>
      </item>
    </selector>

  </item>
</layer-list>