How to code to check whether older installer version is already available on machine

We are developing customized installer using visual studio 2008 installer project. The requirement which we are trying to adress is; suppose user starts installation and if already older version is available on same machine then we should promp user to upgrade the version and needs to show list of files which are 开发者_StackOverflow中文版new in this version. For the same we are currently trying to retrieve the installer vesion thorugh code but is unable to do so. Can anyone let us know the appropriate approach using which we would be able to detect whether older version is available on machine.

Try to use a windows registry. When you install the old app the registry must be added and when a new app is being installed check the registry and see the registry version value if the registry is found then just show an error message and terminate the installation wizard.