Get this UIAlert working - ios

Question

I am recieving an error on this line in my ViewControllerLogin.m file or anywhere a UIAlert shows up...
[UIAlertView error:#"Enter username and password over 4 chars each."];
The above code gives me an error in the issues editor: "no known class for method selector". I identified the method 'error' in another class in Xcode. Does anyone know why I am getting this error?
UPDATE ViewControllerLogin.m (the UIViewAlets are at the bottom)
#import "ViewControllerLogin.h"
#import "UIAlertView+error.h"
#import "API.h"
#include <CommonCrypto/CommonDigest.h>
#define kSalt #"adlfu3489tyh2jnkLIUGI&%EV(&0982cbgrykxjnk8855"
#implementation ViewControllerLogin
- (void)viewWillAppear:(BOOL)animated {
[self.navigationController setNavigationBarHidden:NO animated:animated];
[super viewWillAppear:animated];
}
- (void)viewWillDisappear:(BOOL)animated {
[self.navigationController setNavigationBarHidden:NO animated:animated];
[super viewWillDisappear:animated];
}
-(void)viewDidLoad {
[super viewDidLoad];
//focus on the username field / show keyboard
[fldUsername becomeFirstResponder];
[self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:#"qwertygreen.png"] forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.titleTextAttributes = #{NSForegroundColorAttributeName: [UIColor whiteColor]};
self.title = #"play";
//changes the buttn color
self.navigationController.navigationBar.tintColor = [UIColor whiteColor];
// Do any additional setup after loading the view.
// Do any additional setup after loading the view, typically from a nib.
}
#pragma mark - View lifecycle
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
-(IBAction)btnLoginRegisterTapped:(UIButton*)sender {
//form fields validation
if (fldUsername.text.length < 4 || fldPassword.text.length < 4)
{
[UIAlertView error:#"Enter username and password over 4 chars each."];
return;
}
//salt the password
NSString* saltedPassword = [NSString stringWithFormat:#"%#%#", fldPassword.text, kSalt];
//prepare the hashed storage
NSString* hashedPassword = nil;
unsigned char hashedPasswordData[CC_SHA1_DIGEST_LENGTH];
//hash the pass
NSData *data = [saltedPassword dataUsingEncoding: NSUTF8StringEncoding];
if (CC_SHA1([data bytes], [data length], hashedPasswordData)) {
hashedPassword = [[NSString alloc] initWithBytes:hashedPasswordData length:sizeof(hashedPasswordData) encoding:NSASCIIStringEncoding];
} else {
[UIAlertView error:#"Password can't be sent"];
return;
}
//check whether it's a login or register
NSString* command = (sender.tag==1)?#"register":#"login";
NSMutableDictionary* params =[NSMutableDictionary dictionaryWithObjectsAndKeys:command, #"command", fldUsername.text, #"username", hashedPassword, #"password", nil];
//make the call to the web API
[[API sharedInstance] commandWithParams:params onCompletion:^(NSDictionary *json) {
//result returned
NSDictionary* res = [[json objectForKey:#"result"] objectAtIndex:0];
if ([json objectForKey:#"error"]==nil && [[res objectForKey:#"IdUser"] intValue]>0) {
[[API sharedInstance] setUser: res];
[self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
//show message to the user
[[[UIAlertView alloc] initWithTitle:#"Logged in" message:[NSString stringWithFormat:#"Welcome %#",[res objectForKey:#"username"]] delegate:nil cancelButtonTitle:#"Close" otherButtonTitles: nil] show];
} else {
//error
[UIAlertView error:[json objectForKey:#"error"]];
}
}];
}
#end

Answer 1

You need to import UIKit.
#import <UIKit/UIKit.h>