i create an app and install it on phone. now i want to add a feature that my app should not uninstall from the phone. so i think if one of the following issues could be solv
Yes, this can be done.
Create a new firmware image for a phone, include your app in the /system/app directory and, since this directory is read-only during runtime, the app cannot be uninstalled. i.e. it is pre-installed.
Otherwise no, this cannot be done. However, with a non-system app, the system does notify other applications after your app has been uninstalled via a PACKAGE_REMOVED broadcast.
So it's possible to determine that your app was uninstalled, but — without flashing the whole phone with a new firmware — there is no way to prevent your application from being uninstalled. Which is a good thing.