Вы можете пройти с этим кодом
- (BOOL)isValid {
UIAlertView *alert;
NSString *_regex =@"\\w+([-+.']\\w+)*@\\w+([-.]\\w+)*\\.\\w+([-.]\\w+)*";
NSPredicate *_predicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", _regex];
//Alert View.
if (self.usernameText.text == nil || [self.usernameText.text length] == 0 ||
[[self.usernameText.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0 ) {
alert = [[UIAlertView alloc]initWithTitle:@"Attention" message:@"Please enter email address." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
return FALSE;
}
else if (![_predicate evaluateWithObject:self.usernameText.text] == YES) {
alert = [[UIAlertView alloc]initWithTitle:@"Attention" message:@"Please enter your correct email address." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
return FALSE;
} else if (self.passwordText.text == nil || [self.passwordText.text length] == 0
||[[self.passwordText.text stringByTrimmingCharactersInSet:[NSCharacterSet
whitespaceAndNewlineCharacterSet]] length] == 0 ) {
alert = [[UIAlertView alloc]initWithTitle:@"Attention" message:@"Please enter your
password." delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
return FALSE;
}
return TRUE;
}
, а затем проверьте правильность действия кнопки входа в систему
-(IBAction)loginAction:(id)sender{
if(loginBtn.tag == 10){
if ([self isValid]) {
[self performSelector:@selector(checkLogin) withObject:nil afterDelay:0.0];
}
}
}