如何移除Android ActionBar底部边框？已解决：修改Activity主题

It sounds like you hit a common gotcha when trying to remove the ActionBar's bottom border/shadow—let’s walk through the solution that worked for you, since it’s easy to mix up which theme controls this element:

First, you mentioned two methods that didn’t work at first:

• Calling setElevation(0) programmatically
• Adding <item name="android:windowContentOverlay">@null</item> to your ActionBar-specific theme

The root issue was misidentifying where the border is styled: it’s not part of the ActionBar’s theme, but your Activity’s theme.

The Working Fix #

To eliminate the bottom border, you need to add the windowContentOverlay attribute to your Activity’s style definition (not the nested ActionBar theme):

<!-- For AppCompat-based themes -->
<item name="windowContentOverlay">@null</item>

<!-- For older Android themes using the android namespace -->
<item name="android:windowContentOverlay">@null</item>

Once you apply this change to your Activity’s theme, the bottom border will disappear completely. This works because the shadow/border is actually drawn by the window content overlay tied to the Activity, not the ActionBar itself.

内容的提问来源于stack exchange，提问作者JMR