Bonus : Facebook Login with email address using Parse.com and adding Users.

//  SignupViewController.m

#import "SignupViewController.h"
#import <Parse/Parse.h>

@interface SignupViewController ()

@end

@implementation SignupViewController


- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}


- (IBAction)signup:(id)sender {
    NSString *password = [self.passwordField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    NSString *email = [self.emailField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    NSString *email2 = email;
    NSString *name = [self.nameField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];


    if ([password length] == 0 || [email length] == 0)
            {
                UIAlertView *alertViewUsername = [[UIAlertView alloc] initWithTitle:@"Oops !" message:@"One field is empty" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
                [alertViewUsername show];
            }

    else {
        PFUser *newUser = [PFUser user];
        newUser.password = password;
        newUser.username = email;
        newUser.email = email2;
        newUser[@"name"] = name;

        [newUser signUpInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
            if(error)           {
                UIAlertView *alertViewSignUp = [[UIAlertView alloc] initWithTitle:@"Sorry!" message:[error.userInfo objectForKey:@"error"] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
                [alertViewSignUp show];
                                }
            else{
                [self.navigationController popToRootViewControllerAnimated:YES];
                }
                            }];
    }

}
@end











//  LoginViewController.m


#import "LoginViewController.h"
#import <Parse/Parse.h>

@interface LoginViewController ()

@end

@implementation LoginViewController

- (void)viewDidLoad
    {
    [super viewDidLoad];
        self.navigationItem.hidesBackButton=YES;
    }


- (IBAction)login:(id)sender {
    NSString *user = [self.emailField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    NSString *password = [self.passwordField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];



    if ([user length] == 0 || [password length] == 0)
        {
        UIAlertView *alertViewUsername = [[UIAlertView alloc] initWithTitle:@"Oops !" message:@"One field is empty" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alertViewUsername show];
        }

    else{
            [PFUser logInWithUsernameInBackground:user
 password:password block:^(PFUser *user, NSError *error) {
     if(error)           {
         UIAlertView *alertViewSignUp = [[UIAlertView alloc] initWithTitle:@"Sorry!" message:[error.userInfo objectForKey:@"error"] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
         [alertViewSignUp show];
                         }
     else   {
         [self.navigationController popToRootViewControllerAnimated:YES];
            }
                     }];
        }

                            }


- (IBAction)loginButtonTouchHandler:(id)sender
{
    // Set permissions required from the facebook user account
    NSArray *permissionsArray = @[@"public_profile", @"email", @"user_friends"];

    // Login PFUser using facebook
    [PFFacebookUtils logInWithPermissions:permissionsArray block:^(PFUser *user, NSError *error) {

        if (user) {
            [FBRequestConnection startForMeWithCompletionHandler:^(FBRequestConnection *connection, id result, NSError *error) {
                if (!error) {
                    [self.navigationController popToRootViewControllerAnimated:YES];
                    // Store the current user's Facebook ID on the user
                    [[PFUser currentUser] setObject:[result objectForKey:@"email"]
                                             forKey:@"email"];
                    [[PFUser currentUser] setObject:[result objectForKey:@"name"]
                                             forKey:@"name"];
                    [[PFUser currentUser] saveInBackground];

                }
            }];
        }
    }];

}

@end










//  FriendsViewController.m
#import "FriendsViewController.h"
#import "EditFriendsViewController.h"

@interface FriendsViewController ()

@end

@implementation FriendsViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.friendsRelation = [[PFUser currentUser] objectForKey:@"friendsRelation"];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    PFQuery *query = [self.friendsRelation query];
    [query orderByAscending:@"username"];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (error) {
            NSLog(@"Error %@ %@", error, [error userInfo]);
        }
        else {
            self.friends = objects;
            [self.tableView reloadData];
        }
    }];

}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"showEditFriends"]) {
        EditFriendsViewController *viewController = (EditFriendsViewController *)segue.destinationViewController;
        viewController.friends = [NSMutableArray arrayWithArray:self.friends];
    }
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return [self.friends count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    PFUser *user = [self.friends objectAtIndex:indexPath.row];
    cell.textLabel.text = user.username;

    return cell;
}


@end```













//  EditFriendsViewController.m

#import "EditFriendsViewController.h"

@interface EditFriendsViewController ()

@end

@implementation EditFriendsViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    PFQuery *query = [PFUser query];
    [query orderByAscending:@"username"];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (error) {
            NSLog(@"Error: %@ %@", error, [error userInfo]);
        }
        else {
            self.allUsers = objects;
            [self.tableView reloadData];
        }
    }];

    self.currentUser = [PFUser currentUser];
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return [self.allUsers count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    PFUser *user = [self.allUsers objectAtIndex:indexPath.row];
    cell.textLabel.text = user.email;

    if ([self isFriend:user]) {
        cell.accessoryType = UITableViewCellAccessoryCheckmark;
    }
    else {
        cell.accessoryType = UITableViewCellAccessoryNone;
    }

    return cell;
}

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    [self.tableView deselectRowAtIndexPath:indexPath animated:NO];

    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

    PFRelation *friendsRelation = [self.currentUser relationforKey:@"friendsRelation"];
    PFUser *user = [self.allUsers objectAtIndex:indexPath.row];

    if ([self isFriend:user]) {
        cell.accessoryType = UITableViewCellAccessoryNone;

        for(PFUser *friend in self.friends) {
            if ([friend.objectId isEqualToString:user.objectId]) {
                [self.friends removeObject:friend];
                break;
            }
        }

        [friendsRelation removeObject:user];
    }
    else {
        cell.accessoryType = UITableViewCellAccessoryCheckmark;
        [self.friends addObject:user];
        [friendsRelation addObject:user];
    }

    [self.currentUser saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
        if (error) {
            NSLog(@"Error: %@ %@", error, [error userInfo]);
        }
    }];
}

#pragma mark - Helper methods

- (BOOL)isFriend:(PFUser *)user {
    for(PFUser *friend in self.friends) {
        if ([friend.objectId isEqualToString:user.objectId]) {
            return YES;
        }
    }

    return NO;
}

@end```