Android Studio：You need to use a Theme.AppCompat theme (or descendant) with this activity. AlertDialog

学习《第一行代码》的时候遇到的问题。

Process: com.example.sevenun.littledemo, PID: 2085
java.lang.RuntimeException: Unable to start receiver com.example.sevenun.littledemo.receiver.ForceOfflineReceiver: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2426)
at android.app.ActivityThread.access$1700(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1272)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.support.v7.app.AppCompatDelegateImplV7.createSubDecor(AppCompatDelegateImplV7.java:340)
at android.support.v7.app.AppCompatDelegateImplV7.ensureSubDecor(AppCompatDelegateImplV7.java:309)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:273)
at android.support.v7.app.AppCompatDialog.setContentView(AppCompatDialog.java:80)
at android.support.v7.app.AlertController.installContent(AlertController.java:214)
at android.support.v7.app.AlertDialog.onCreate(AlertDialog.java:256)
at android.app.Dialog.dispatchOnCreate(Dialog.java:361)
at android.app.Dialog.show(Dialog.java:262)
at com.example.sevenun.littledemo.receiver.ForceOfflineReceiver.onReceive(ForceOfflineReceiver.java:38)
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2419)
at android.app.ActivityThread.access$1700(ActivityThread.java:135) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1272) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:136) 
at android.app.ActivityThread.main(ActivityThread.java:5017) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
at dalvik.system.NativeStart.main(Native Method) 

有两个解决办法：

1. 把我们当前的Activity所继承的ActionBarActivity，改为继承Activity（android.app.Activity）。

2.我出现错误的地方是因为使用了AlertDialog，发现我导入的android.support.v7.app.AlertDialog，然后我就改为导入android.app.AlertDialog就成功了。