1、在使用Activity集成AppCompatActivity时
首先引包老是出错，找不到AppCompatActivity，明明SDK下边有该包。这个错误发生在打开两个Android Studio时，关掉其中一个就正常了。
2、This Activity already has an action bar supplied by the window decor
正常引入AppCompatActivity后，如果调用:
Toolbar toolbar = (Toolbar)findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
就会闪退，捕获异常发现错误是：
This Activity already has an action bar supplied by the window decor……
查找到的解决方式：
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>