EmojiAvoider.m

+ (NSString*)stringByRemovingEmojiFrom:(NSString*)string {
    NSMutableString* __block buffer = [NSMutableString stringWithCapacity:[string length]];
    
    [string enumerateSubstringsInRange:NSMakeRange(0, [string length])
                             options:NSStringEnumerationByComposedCharacterSequences
                          usingBlock: ^(NSString* substring, NSRange substringRange, NSRange enclosingRange, BOOL* stop) {
                              [buffer appendString:([[self class] isEmoji:substring])? @"": substring];
                          }];
    
    return buffer;
}

+ (BOOL)isEmoji:(NSString*)string {
//I will suggest to create this once and use it instead of creating it everytime like this.
    NSMutableCharacterSet *alphaNumericWhitespaceCharacterSet = [[NSCharacterSet alphanumericCharacterSet] mutableCopy];
    [alphaNumericWhitespaceCharacterSet formUnionWithCharacterSet:[NSCharacterSet whitespaceCharacterSet]];
// Union with other charsets if want to include other charachters.
    return [string rangeOfCharacterFromSet:alphaNumericWhitespaceCharacterSet].location == NSNotFound;
}

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (string.length != 0) {
        string = [[self class] stringByRemovingEmojiFrom:string];
        textField.text = [textField.text stringByReplacingCharactersInRange:range withString:string];
        return NO;
    }
    return YES;
}