判断是否第一次登陆app，具体方法如下：

if (![[NSUserDefaults standardUserDefaults]boolForKey:@"firstLaunch"]) {


        NSLog(@"first time to launch ");

        [[NSUserDefaults standardUserDefaults]setBool:YES forKey:@"firstLaunch"];

        [[NSUserDefaults standardUserDefaults]setBool:NO forKey:@"everLaunch"];



    }else {


        NSLog(@"ever launched ");

        [[NSUserDefaults standardUserDefaults]setBool:YES forKey:@"everLaunch"];



    }