Delete key event in iPhone - iphone

Question

I created UITextField. I need only 4 numeric characters only allowed that textfield.
I used the following code and get result.
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
NSNumber* candidateNumber;
NSString* candidateString = [textField.text stringByReplacingCharactersInRange:range withString:string];
range = NSMakeRange(0, [candidateString length]);
[numberFormatter getObjectValue:&candidateNumber forString:candidateString range:&range error:nil];
NSUInteger newLength = [passwordfield.text length];
if(newLength>=4)
{
[passwordfield setText:[passwordfield.text substringToIndex:3]];
UIAlertView *alert = [[UIAlertView alloc] init];
[alert setTitle:#"Alert"];
[alert setMessage:#"Four Characters only allowed.."];
[alert setDelegate:self];
[alert addButtonWithTitle:#"Ok"];
[alert show];
}
if (([candidateString length] > 0) && (candidateNumber == nil || range.length < [candidateString length]))
{
return NO;
}
else
{
return YES;
}
}
But my problem is when I press delete key, last two characters are deleting
and same time alertview also display.
How to solve this issue?

Answer 1

You're making this more complex than it needs to be. When a user taps the backspace key, the incoming string is a blank string; [NSString string]. Here's a working solution:
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
if (![numberFormatter numberFromString:string] && ![string isEqualToString:[NSString string]]) {
return NO;
}
if (textField.text.length + string.length > 4) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Alert"
message:#"Four Characters only allowed..."
delegate:self
cancelButtonTitle:#"Ok"
otherButtonTitles:nil];
[alert show];
[alert release];
return NO;
} else {
return YES;
}
}