方式1

styles里增加:

<item name="android:windowFullscreen">true</item>
<item name="windowNoTitle">true</item>

完整代码样例:

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="android:windowFullscreen">true</item>
    <item name="windowNoTitle">true</item>
</style>

Manifest定义:

<application
    ...
    android:theme="@style/AppTheme">
</application>

方式2

activity代码中设置(在setContentView方法前调用):

supportActionBar?.hide()
window.setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);