学习《第一行代码》的时候，出现的错误。

java.lang.RuntimeException: Unable to start receiver com.example.sevenun.littledemo.receiver.ForceOfflineReceiver: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@5e2d85a -- permission denied for this window type
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2732)
at android.app.ActivityThread.-wrap14(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1421)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@5e2d85a -- permission denied for this window type
at android.view.ViewRootImpl.setView(ViewRootImpl.java:591)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:310)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)
at android.app.Dialog.show(Dialog.java:319)
at com.example.sevenun.littledemo.receiver.ForceOfflineReceiver.onReceive(ForceOfflineReceiver.java:38)
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2725)
at android.app.ActivityThread.-wrap14(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1421) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

因为《第一行代码》里面的程序主要是在Android4.x运行的，而最新的Android 6 对程序的权限有了新的要求。

所以，我们要启动类型为WindowManager.LayoutParams.TYPE_SYSTEM_ALERT的AlertDialog的时候：

如果是在Android4.x的情况，只用在AndroidManifest.xml里面声明<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />。

如果是在Android 6(API 23)的情况下，则可以添加以下代码进行请求权限，让用户同意后才可以弹出AlertDialog。

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_login);

        if (Build.VERSION.SDK_INT >= 23) {

            if (! Settings.canDrawOverlays(LoginActivity.this)) {

                Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,

                        Uri.parse("package:" + getPackageName()));

                startActivityForResult(intent,10);

            }

        }

    }

    @Override

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        if (requestCode == 10) {

            if (Build.VERSION.SDK_INT >= 23) {

                if (!Settings.canDrawOverlays(this)) {

                    // SYSTEM_ALERT_WINDOW permission not granted...

                    Toast.makeText(LoginActivity.this,"not granted",Toast.LENGTH_SHORT);

                }

            }

        }

    }

参考：http://blog.csdn.net/chenlove1/article/details/52047105