iOS app first launch

问题

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?

回答1:

Swift 4 and higher

func isAppAlreadyLaunchedOnce()->Bool{
    let defaults = UserDefaults.standard
    if let _ = defaults.string(forKey: "isAppAlreadyLaunchedOnce"){
        print("App already launched")
        return true
    }else{
        defaults.set(true, forKey: "isAppAlreadyLaunchedOnce")
        print("App launched first time")
        return false
    }
}

Note: This method would return false after user re-installs app and launch first time.

回答2:

Try this for Swift 2 and below

func isAppAlreadyLaunchedOnce()->Bool{
    let defaults = NSUserDefaults.standardUserDefaults()

    if let isAppAlreadyLaunchedOnce = defaults.stringForKey("isAppAlreadyLaunchedOnce"){
        println("App already launched")
        return true
    }else{
        defaults.setBool(true, forKey: "isAppAlreadyLaunchedOnce")
        println("App launched first time")
        return false
    }
}

回答3:

Since NSUserDefaults for an app are erased when uninstalling the app, you could try testing for the existence of a certain value when the app launches.

If the value exists, the app had already been installed. If not, this is the first time the app is launched, and you set that value.

回答4:

SWIFT :

let launchedBefore = UserDefaults.standard.bool(forKey: "launchedBefore")
if launchedBefore  {
    print("Not first launch.")
} else {
    print("First launch, setting UserDefault.")
    UserDefaults.standard.set(true, forKey: "launchedBefore")
}

OBJECTIVE - C :

if ([[NSUserDefaults standardUserDefaults] boolForKey:@"isAppAlreadyLaunchedOnce"])
{
    return true;
}
else
{
    [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"isAppAlreadyLaunchedOnce"];
    [[NSUserDefaults standardUserDefaults] synchronize];
    return false;
}

来源：https://stackoverflow.com/questions/26830285/ios-app-first-launch