How to check if UITextField's text is valid email?

Question

I have a view controller with 3 UITextFields (username, email, and password).

I need a method that checks first, if all fields have text in them, then check if the e

Answer 1

This will check a UITextField for a proper email.
Add this method to the textFields delegate then check if the characters it is about to change should be added or not.
Return YES or NO depending on the text fields current text compared to a valid email address:

#define ALPHA                   @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
#define NUMERIC                 @"1234567890"
#define ALPHA_NUMERIC           ALPHA NUMERIC

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSCharacterSet *unacceptedInput = nil;
    if ([[textField.text componentsSeparatedByString:@"@"] count] > 1) {
        unacceptedInput = [[NSCharacterSet characterSetWithCharactersInString:[ALPHA_NUMERIC stringByAppendingString:@".-"]] invertedSet];
    } else {
        unacceptedInput = [[NSCharacterSet characterSetWithCharactersInString:[ALPHA_NUMERIC stringByAppendingString:@".!#$%&'*+-/=?^_`{|}~@"]] invertedSet];
    }
    return ([[string componentsSeparatedByCharactersInSet:unacceptedInput] count] <= 1);
}  

To check if a text field is empty or not just use if (myTextField.text.length > 0) {} anywhere in your view controller.