How to check programmatically if an App is installed?

I am developing an iPhone application which will install few third party applications in an enterprise. I have the information about the bundle IDs. Is there a way to check if the application is already installed, using some system APIs? Currently the application gets installed again, overwriting the current installation. I need to prevent this some how. (Apple's AppStore application disables the installation option if the app is already installed.)

I think this is not possible directly, but if the apps register uri schemes you could test for that.

A URI scheme is for example fb:// for the facebook app. You can register that in the info.plist of your app. [UIApplication canOpenURL:url] will tell you if a certain url will or will not open. So testing if fb:// will open, will indicate that there is an app installed which registered fb:// - which is a good hint for the facebook app.

// check whether facebook is (likely to be) installed or not
if ([[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"fb://"]]) {
    // Safe to launch the facebook app
    [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"fb://profile/200538917420"]];
}

Here's an example to test if the facebook app is installed

if ([[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"fb://"]]) {
    // Facebook app is installed
}