iphone - How can I implement login with email address or username using Parse.com? -

until have checked login credentials username , password using following syntax.

loginwithusernameinbackground

 [pfuser loginwithusernameinbackground:[usernamefield.text lowercasestring] password:passwordfield.text block:^(pfuser* user, nserror* error){ 

but requirement that:

user must need login 1 of both email , username.

and need check username / email , password

how can achieved?

pfquery *query = [pfuser query];     [query wherekey:@"email" equalto:usernamefield.text];     [query findobjectsinbackgroundwithblock:^(nsarray *objects, nserror *error){         if (objects.count > 0) {              pfobject *object = [objects objectatindex:0];             nsstring *username = [object objectforkey:@"username"];             [pfuser loginwithusernameinbackground:username password:passwordfield.text block:^(pfuser* user, nserror* error){             }];         }else{             [pfuser loginwithusernameinbackground: usernamefield.text password:passwordfield.text block:^(pfuser* user, nserror* error){             }];          }       }];