Iphone UITextField only integer

Question

I have a UITextField in my IB and I want to check out if the user entered only numbers (no char)and get the integer value.

I get the integer value of the UITextField

Answer 1

Implementing shouldChangeCharactersInRange method as below does not allow the user input non-numeric characters.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { 
    NSCharacterSet *nonNumberSet = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
    return ([string stringByTrimmingCharactersInSet:nonNumberSet].length > 0) || [string isEqualToString:@""];
}

This returns YES if the string is numeric, NO otherwise. the [string isEqualToString@""] is to support the backspace key to delete.

I love this approach because it's clean.

Answer 2

To only allow for numeric input:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { 
    return [string isEqualToString:@""] || 
        ([string stringByTrimmingCharactersInSet:
            [[NSCharacterSet decimalDigitCharacterSet] invertedSet]].length > 0);
}

To test for an integer:

- (BOOL)isNumeric:(NSString *)input {
    for (int i = 0; i < [input length]; i++) {
        char c = [input characterAtIndex:i];
        // Allow a leading '-' for negative integers
        if (!((c == '-' && i == 0) || (c >= '0' && c <= '9'))) {
            return NO;
        }
    }
    return YES;
}

Answer 3

You could also use UITextFieldDelegate method

textField:shouldChangeCharactersInRange:replacementString:

to live check that each time the user press a key, it is a simple digit, so that he/she knows that only int value is to be entered in the field.