How to detect Apps first launch in iOS?

Question

I would like to display a welcome screen when a user opens my app for the first time. What method is there to check the first launch of an app in Swift?

Answer 1

I often found userDefault inaccessible due to some bugs for Apples data protection policy in my app, So I changed my strategy to detect first launch with below

if ( fileExists( dummyFilePath ) == NO ) {
    createFileAt( dummyFilePath )
    // This is first launch
}