Allow only alpha numeric characters in UITextView - objective-c

Question

Is there anyway i can allow user to enter only alpha numeric characters in a text view and no other character.
EDIT:
Tried,
if ([_txtView.text rangeOfCharacterFromSet:alphaSet].location != NSNotFound)
{
UIAlertView* alert = [[UIAlertView alloc] initWithTitle:#"Hello" message:#"Only alpha numeric characters are allowed" delegate:nil cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alert show];
return;
}
but this only works for some of the times
Thanks!!

Answer 1

You can achieve that using [[[NSCharacterSet alphanumericCharacterSet] invertedSet]. This method will return a character set containing only characters that don’t exist in the receiver.
NSCharacterSet *charactersToBlock = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
//Conform UITextField delegate and implement this method.
- (BOOL)textField:(UITextField *)field shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)characters
{
return ([characters rangeOfCharacterFromSet:charactersToBlock].location == NSNotFound);
}

Answer 2

Try this:
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
if (textField == txtWebsite) {
NSCharacterSet *set = [NSCharacterSet characterSetWithCharactersInString:#"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890 "];
if ([string rangeOfCharacterFromSet:set].location != NSNotFound) {
return YES;
}
else {
return NO;
}
}
else {
return YES;
}
}
write code in delegate method of uitextfield.

Answer 3

set delegate for textview and override/implement test should change in range method
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
NSCharacterSet *alphaSet = [NSCharacterSet alphanumericCharacterSet];
BOOL valid = [[text stringByTrimmingCharactersInSet:alphaSet] isEqualToString:#""];
return valid;
}

Answer 4

Equivalent Swift 3 version of the answer provided by #user1113101
Though it's late to answer and there are other simple and great approaches, but this answer might be useful to someone.
This is simple and worked like a charm for me.
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
/// 1. replacementText is NOT empty means we are entering text or pasting text: perform the logic
/// 2. replacementText is empty means we are deleting text: return true
if text.characters.count > 0 {
var allowedCharacters = CharacterSet.alphanumerics
let unwantedStr = text.trimmingCharacters(in: allowedCharacters)
return unwantedStr.characters.count == 0
}
return true
}
Note: This will work for pasting strings into the text field as well. Pasted string will not be displayed in text field if it contains any unwanted characters.

Answer 5

// Add this in ViewDidLoad or any init method
NSCharacterSet *blockedCharacters = [[[NSCharacterSet alphanumericCharacterSet] invertedSet] retain];
then Set your textfield's delegate in nib file .
- (BOOL)textField:(UITextField *)field shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)characters
{
return ([characters rangeOfCharacterFromSet:blockedCharacters].location == NSNotFound);
}
Or there is another way in shouldChangeCharactersInRange method. You can check
{
NSString *stringPlace = #"[a-z A-Z]*";
NSPredicate *testPlace = [NSPredicate predicateWithFormat:#"SELF MATCHES %#", stringPlace];
BOOL matches = [testPlace evaluateWithObject:string];
if (!matches && string.length > 5)
{
return NO;
}
return YES;
}