iPhone SDK: Set Max Character length TextField

Question

Hi there, anybody know how I can set the maximum amount of characters in a TextField on the iPhone SDK when I load up the UIView ?

Answer 1

You can't do this directly -- UITextField has no "maxLength" attribute --, but you can set the UITextField's delegate, then use:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

Answer 2

How do I get to make it's 'range' or whatever, something like... 20 characters long?

Answer 3

The best way would be to set up a notification on the text changing. In your -awakeFromNib of your view controller method you'll want:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(limitTextField:) name:@"UITextFieldTextDidChangeNotification" object:myTextField];

Then in the same class add:

- (void)limitTextField:(NSNotification *)note {
    int limit = 20;
    if ([[myTextField stringValue] length] > limit) {
        [myTextField setStringValue:[[myTextField stringValue] substringToIndex:limit]];
    }
}

Then link up the outlet myTextField to your UITextField and it will not let you add any more characters after you hit the limit. Be sure to add this to your dealloc method:

[[NSNotificationCenter defaultCenter] removeObserver:self name:@"UITextFieldTextDidChangeNotification" object:myTextField];

Answer 4

Thank you august! (Post)

This is the code that I ended up with which works:

#define MAX_LENGTH 20

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (textField.text.length >= MAX_LENGTH && range.length == 0)
    {
     return NO; // return NO to not change text
    }
    else
    {return YES;}
}

Answer 5

To complete August answer, an possible implementation of the proposed function (see UITextField's delegate).

I did not test domness code, but mine do not get stuck if the user reached the limit, and it is compatible with a new string that comes replace a smaller or equal one.

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    //limit the size :
    int limit = 20;
    return !([textField.text length]>limit && [string length] > range.length);
}

Answer 6

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { //limit the size : int limit = 20; return !([textField.text length]>limit && [string length] > range.length); }

this method does not work if we have to check this condition on more than 1 text field on the same view. Any suggestion to resolve this problem?

Answer 7

To make it work with cut & paste of strings of any length, I would suggest changing the function to something like:

#define MAX_LENGTH 20

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
    {
        NSInteger insertDelta = string.length - range.length;

        if (textField.text.length + insertDelta > MAX_LENGTH)
        {
           return NO; // the new string would be longer than MAX_LENGTH
        }
        else {
            return YES;
        }
    }

Answer 8

While the UITextField class has no max length property, it's relatively simple to get this functionality by setting the text field's delegate and implementing the following delegate method:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSUInteger newLength = [textField.text length] + [string length] - range.length;
    return (newLength > 25) ? NO : YES;
}

Before the text field changes, the UITextField asks the delegate if the specified text should be changed. The text field has not changed at this point, so we grab it's current length and the string length we're inserting, minus the range length. If this value is too long (more than 25 characters in this example), return NO to prohibit the change.

When typing in a single character at the end of a text field, the range.location will be the current field's length, and range.length will be 0 because we're not replacing/deleting anything. Inserting into the middle of a text field just means a different range.location, and pasting multiple characters just means string has more than one character in it.

Deleting single characters or cutting multiple characters is specified by a range with a non-zero length, and an empty string. Replacement is just a range deletion with a non-empty string.

Answer 9

I found this quick and simple

• (IBAction)backgroundClick:(id)sender {

  if (mytext.length <= 7) {

  [mytext resignFirstResponder];

  }

  else { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Too Big" message:@"Please Shorten Name" delegate:nil cancelButtonTitle:@"Cancel" otherButtonTitles:nil]; [alert show]; [alert release]; }

Answer 10

Using Interface builder you can link and get the event for "Editing changed" in any of your function. Now there you can put check for the length

- (IBAction)onValueChange:(id)sender 
{
    NSString *text = nil;
    int MAX_LENGTH = 20;
    switch ([sender tag] ) 
    {
        case 1: 
        {
            text = myEditField.text;
            if (MAX_LENGTH < [text length]) {
                myEditField.text = [text substringToIndex:MAX_LENGTH];
            }
        }
            break;
        default:
            break;
    }

}