How to enter Numbers only in UITextField and limit maximum length? - objective-c

Question

In UITextField we Enter Numeric only and limit up to 3 numeric for this i used below code
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
NSUInteger newLength = [textField.text length] + [string length] - range.length;
NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:NUMBERS_ONLY] invertedSet];
NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:#""];
while (newLength < CHARACTER_LIMIT) {
return [string isEqualToString:filtered];
}
/* Limits the no of characters to be enter in text field */
return (newLength > CHARACTER_LIMIT ) ? NO : YES;
}
When i press long press on textfield (like below image )and enter string between two numbers it's allowing all special characters and charterers also.

Answer 1

Not that I don't like the answer I wrote at this question, that was copy & pasted here also. I'll try to explain your error.
This answer is based on the assumption that your constants are defined something like this:
#define NUMBERS_ONLY #"1234567890"
#define CHARACTER_LIMIT 3
The reason your logic is failing is that you never handle the event when newLength will be equal to the CHARACTER_LIMIT.
To illustrate suppose your textfield is empty and you request to paste the string #"ABC" to the textfield, your delegate method is called. You create the string filtered which correctly evaluates to an empty string, and you can't wait to execute the line return [string isEqualToString:filtered]; but you never actually evaluate that line because you don't meet the entry requirements for the while loop, because newLength is 3. so the simple return (newLength > CHARACTER_LIMIT ) ? NO : YES; decides the return value.
If your CHARACTER_LIMIT is actually 4 for some reason, just imagine #"ABCD" as the string the logic still applies.
Here is a simple example of your function corrected to work. Again I'm assuming that CHARACTER_LIMIT is equal to 3.
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
NSUInteger newLength = [textField.text length] + [string length] - range.length;
NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:NUMBERS_ONLY] invertedSet];
NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:#""];
return (([string isEqualToString:filtered])&&(newLength <= CHARACTER_LIMIT));
}

Answer 2

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
// Check for non-numeric characters
NSUInteger lengthOfString = string.length;
for (NSInteger loopIndex = 0; loopIndex < lengthOfString; loopIndex++) {
unichar character = [string characterAtIndex:loopIndex];
if (character < 48) return NO; // 48 unichar for 0
if (character > 57) return NO; // 57 unichar for 9
}
// Check for total length
NSUInteger proposedNewLength = textField.text.length - range.length + string.length;
if (proposedNewLength > 3) return NO;
return YES;
}
Its working fine for me u can use this code

Answer 3

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
NSString *s = [textField.text stringByReplacingCharactersInRange:range withString:string];
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:#"^\\d{0,3}$" options:0 error:nil];
NSTextCheckingResult *match = [regex firstMatchInString:s options:0 range:NSMakeRange(0, [s length])];
return (match != nil);
}

Answer 4

Check the UITextFieldDelegate method
- (BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
This method will be invoked each time after you type/tap a character or press cut/paste and before that action changes the characters displayed. Here you can very well to your check for maxLength and numbers-only text input(by using RegularExpression patter as given below) and return YES or NO basd on that. If you return YES it will do the change otherwise it will not. Hope this clears your doubt.

Answer 5

I prefer using an NSNumberFormatter to validate the text can be parsed into a number. NSNumberFormatter returns nil if the string cannot be converted to a number. This lets you react to the input (i.e. make text red, throw up a alert)
NSNumber* value = nil;
NSNumberFormatter* format = [[NSNumberFormatter alloc] init];
value = [format numberFromString:someValueString];//returns and
if (value == nil){
//do something useful i.e. show alert
}