How to restrict UIalertview in this code? - ios

Question

I have created a US-format mobile number. This code does not display letters and special characters. It successfully displays but it displays UIAlertviews, when the user enters letters and special characters in UITextfield, it shows some UIAlertview. How can I control the UIAlertviews? I want to display only one Alertview.
This is the code that I already have:
if(textField==mobileNo)
{
NSCharacterSet *myCharSet = [NSCharacterSet characterSetWithCharactersInString:#"0123456789"];
for (int i = 0; i < [string length]; i--) {
unichar c = [string characterAtIndex:i];
if (![myCharSet characterIsMember:c]) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Error" message:#"Alphbets and Special characters not allowed" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
return NO;
}
}
}

Answer 1

You could try the following... but its not a great solution.....
In your header declare a BOOL to check if the alert view has been shown already, like so:
BOOL alertCheck;
In your viewDidLoad set it to NO:
alertCheck = NO;
Then in your code, check it before deciding to display your alertview.
if(textField==mobileNo) {
NSCharacterSet *myCharSet = [NSCharacterSet characterSetWithCharactersInString:#"0123456789"];
for (int i = 0; i < [string length]; i--) {
unichar c = [string characterAtIndex:i];
if (![myCharSet characterIsMember:c]) {
if (alertCheck == NO) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Error" message:#"Alphbets and Special characters not allowed" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
alertCheck = YES;
}
return NO;
}
}
}

Answer 2

You can try the following:
if (![myCharSet characterIsMember:c]) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
//show the UIAlertView
});
}

Answer 3

That code isn't so nice. You're just checking if the string value is a number or not. To do that you can use [NSScanner scannerWithString:] this way:
bool isNumber = [[NSScanner scannerWithString: string] scanInt:nil]
if (!isNumber) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Error" message:#"Alphbets and Special characters not allowed" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
}
Code seems to be clearer and a lot more simpler.
Hope it helped!