App Install Location
Broadcast Receivers listening for "boot completed"
The system delivers the ACTION_BOOT_COMPLETED broadcast before the external storage is mounted to the device. If your application is installed on the external storage, it can never receive this broadcast. http://www.ideasandroid.com/android/sdk/docs/guide/appendix/install-location.html
android明确说明了,安装在sd卡上的应用程序是接收不到ACTION_BOOT_COMPLETED消息的,在mount sd卡之前这个消息已经发出了。