我出现这个问题的原因是在代码中我需要显示一个AlertDialog,但是在Manifest清单文件中，没有添加如下运行时权限，添加之后就OK了。
<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
详细log如下：
02-22 11:16:41.759 5322-5322/com.example.usbpermissiontest W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x4205f300)
02-22 11:16:41.769 5322-5322/com.example.usbpermissiontest E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.usbpermissiontest, PID: 5322
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.usbpermissiontest/com.example.usbpermissiontest.MainActivity}: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@422f6830 -- permission denied for this window type
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
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$MethodAndArgsCaller.run(ZygoteInit.java:794)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@422f6830 -- permission denied for this window type
at android.view.ViewRootImpl.setView(ViewRootImpl.java:563)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:259)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
at android.app.Dialog.show(Dialog.java:286)
at com.example.usbpermissiontest.PermissionGrant.<init>(PermissionGrant.java:42)
at com.example.usbpermissiontest.MainActivity.onCreate(MainActivity.java:18)
at android.app.Activity.performCreate(Activity.java:5240)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
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:794)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
at dalvik.system.NativeStart.main(Native Method)
02-22 11:21:42.089 5322-5322/? I/Process: Sending signal. PID: 5322 SIG: 9