AndroidStudio xml不显示内容出现：Rendering Problems The following classes could not be instantiated

使用AndroidStudio在写布局文件预览时出现下面情况：

 Rendering Problems The following classes could not be instantiated:
- android.support.v7.app.WindowDecorActionBar (Open Class, Show Exception, Clear Cache)
 Tip: Use View.isInEditMode() in your custom views to skip code or show sample data when shown in the IDE.  If this is an unexpected error you can also try to build the project, then manually refresh the layout.  Exception Details java.lang.NullPointerException   at android.support.v7.app.WindowDecorActionBar.getDecorToolbar(WindowDecorActionBar.java:246)   at android.support.v7.app.WindowDecorActionBar.init(WindowDecorActionBar.java:202)   at android.support.v7.app.WindowDecorActionBar.<init>(WindowDecorActionBar.java:194)   at java.lang.reflect.Constructor.newInstance(Constructor.java:423)   at com.android.layoutlib.bridge.bars.AppCompatActionBar.<init>(AppCompatActionBar.java:89)   at com.android.layoutlib.bridge.impl.Layout.createActionBar(Layout.java:238)   at com.android.layoutlib.bridge.impl.Layout.<init>(Layout.java:150) Copy stack to clipboard   Failed to find the style corresponding to the id 2130772069 (22 similar errors not shown)  Failed to load AppCompat ActionBar with unknown error. (3 similar errors not shown)  Tip: Try to refresh the layout. 

出现这种情况，修改下style，然后clean一下,如果还是不行再invalidate cache/restart。

将parent修改如下添加一个Base属性：

操作了之后再进行预览看看。