AppBarLayout custom shadow

BindingAdapters.kt

  @JvmStatic
  @BindingAdapter("isCustomShadowEnabled")
  fun setAppBarDefaultShadowEnabled(appBarLayout: AppBarLayout, isCustomShadowEnabled: Boolean) {
    if (isCustomShadowEnabled) {
      appBarLayout.outlineProvider = null // removes the shadow below the AppBar without affecting elevation
      // add the shadow
      val inflater = LayoutInflater.from(appBarLayout.context)
      val shadowView = inflater.inflate(R.layout.view_shadow, appBarLayout, false)
      appBarLayout.addView(shadowView)
    }
  }

layout.xml

<android.support.design.widget.AppBarLayout
  bind:isCustomShadowEnabled="@{true}" // add this line to your AppBarLayout

styles.xml

  <style name="Shadow">
    <item name="android:background">@color/light_gray</item>
  </style>

  <style name="Shadow.Horizontal">
    <item name="android:layout_width">match_parent</item>
    <item name="android:layout_height">1dp</item>
  </style>

view_shadow.xml

<?xml version="1.0" encoding="utf-8"?>
<View style="@style/Shadow.Horizontal"/>