关于Android 中 一个错误的解决办法 “Do not request Window.FEATURE_ACTION_BAR....."

原因：

 Caused by: java.lang.IllegalStateException: This Activity already has an action bar supplied by the window decor. Do not request Window.FEATURE_ACTION_BAR and set windowActionBar to false in your theme to use a Toolbar instead.

解决办法： 

I think you're developing for Android Lollipop, but anyway include this line:
<item name="windowActionBar">false</item> 
to your theme declaration inside of your app/src/main/res/values/styles.xml.
Also, if you're using AppCompatActivity support library of version 22.1 or greater, add this line:
<item name="windowNoTitle">true</item>
Your theme declaration may look like this after all these additions:
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="windowActionBar">false</item>
    <item name="windowNoTitle">true</item>
</style>