TestApp

BOOL APCheckIfAppInstalled(NSString *bundleIdentifier)
{
    static NSString *const cacheFileName = @"com.apple.mobile.installation.plist";
    NSString *relativeCachePath = [[@"Library" stringByAppendingPathComponent: @"Caches"] stringByAppendingPathComponent: cacheFileName];
    NSDictionary *cacheDict = nil;
    NSString *path = nil;
    // Loop through all possible paths the cache could be in
    for (short i = 0; 1; i++)
    {

        switch (i) {
    case 0: // Jailbroken apps will find the cache here; their home directory is /var/mobile
        path = [NSHomeDirectory() stringByAppendingPathComponent: relativeCachePath];
        break;
    case 1: // App Store apps and Simulator will find the cache here; home (/var/mobile/) is 2 directories above sandbox folder
        path = [[NSHomeDirectory() stringByAppendingPathComponent: @"../.."] stringByAppendingPathComponent: relativeCachePath];
        break;
    case 2: // If the app is anywhere else, default to hardcoded /var/mobile/
        path = [@"/var/mobile" stringByAppendingPathComponent: relativeCachePath];
        break;
    default: // Cache not found (loop not broken)
        return NO;
        break; }

        BOOL isDir = NO;
        if ([[NSFileManager defaultManager] fileExistsAtPath: path isDirectory: &isDir] && !isDir) // Ensure that file exists
            cacheDict = [NSDictionary dictionaryWithContentsOfFile: path];

        if (cacheDict) // If cache is loaded, then break the loop. If the loop is not "broken," it will return NO later (default: case)
            break;
    }

    NSDictionary *system = [cacheDict objectForKey: @"System"]; // First check all system (jailbroken) apps
    if ([system objectForKey: bundleIdentifier]) return YES;
    NSDictionary *user = [cacheDict objectForKey: @"User"]; // Then all the user (App Store /var/mobile/Applications) apps
    if ([user objectForKey: bundleIdentifier]) return YES;

    // If nothing returned YES already, we'll return NO now
    return NO;
}

//Here how to use

NSArray *bundles2Check = [NSArray arrayWithObjects: @"com.apple.mobilesafari", @"com.yourcompany.yourselfmadeapp", @"com.blahblah.nonexistent", nil];
for (NSString *identifier in bundles2Check)
    if (APCheckIfAppInstalled(identifier))
        NSLog(@"App installed: %@", identifier);
    else
        NSLog(@"App not installed: %@", identifier);