想照着音量对话框的做法，作一个在后台显示Dialog的方法，可是在Dialog.show()的时候，出了下面这个异样：

1、异常原因-没加权限

往下的调用顺序是

① android.view.ViewRootImpl.setView(ViewRootImpl.java:481)
② com.android.server.wm.Session.add(Session.java:139)
③ com.android.server.wm.WindowManagerService.addWindow(WindowManagerService:1999)
④ com.android.internal.policy.impl.PhoneWindowManager.checkAddPermission(PhoneWindowMana:1063)

在这里发现了

String permission = null;
switch (type) {
case TYPE_TOAST:
// XXX right now the app process has complete control over
// this... should introduce a token to let the system
// monitor/control what they are doing.
break;
case TYPE_INPUT_METHOD:
case TYPE_WALLPAPER:
// The window manager will check these.
break;
case TYPE_PHONE:
case TYPE_PRIORITY_PHONE:
case TYPE_SYSTEM_ALERT:
case TYPE_SYSTEM_ERROR:
case TYPE_SYSTEM_OVERLAY:
permission = android.Manifest.permission.SYSTEM_ALERT_WINDOW;
break;
default:
permission = android.Manifest.permission.INTERNAL_SYSTEM_WINDOW;
}

音量对话框用的是“TYPE_VOLUME_OVERLAY”，那就加上“INTERNAL_SYSTEM_WINDOW”

可是带进去一跑，还是不行，再找