Validate length and restrict textfield to Numeric, alphanumeric, and alpha characters only

#define ALPHA @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

#define NUMERIC @"1234567890"

#define ALPHA_NUMERIC ALPHA NUMERIC

#define MAX_LENGTH 25

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

    if(textField== textfieldname)

    {           

        NSUInteger newLength = [textField.text length] + [string length] - range.length;

        

        NSCharacterSet *unacceptedInput =

        [[NSCharacterSet characterSetWithCharactersInString:ALPHA_NUMERIC] invertedSet];

        if ([[string componentsSeparatedByCharactersInSet:unacceptedInput] count] > 1)

            return NO;

        else

            return YES&&(newLength < MAX_LENGTH);

        return YES;

    }else{

        return NO;

    }

}