requestWindowFeature(Window.FEATURE_NO_TITLE);

getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
必须在setcontentView()方法之前设置

<?xml version="1.0" encoding="utf-8"?>

<resources>

        <!-- name 是Style的名称，parent 继承那个父类样式 -->

        <style name="theme_fullScreen" parent="android:Theme.Black">

            <item name="android:windowNoTitle">true</item>  <!-- 设置无标题 -->

            <item name="android:windowFullscreen">?android:windowNoTitle</item> <!-- 是否填充慢屏幕，引用android:windowNoTitle 的值 -->

           </style>

</resources>