UITextField 正则表达式 匹配

注：设置（UITextField＊）的 delegate
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range
replacementString:(NSString *)string
{

    NSLog(@"%s",__FUNCTION__);

    NSString *result = [textField.text
stringByReplacingCharactersInRange:range
withString:string];

    

    if ([result
length] ==
0) return
YES; 

    

    NSString *regex =
@"^[a-zA-Z0-9_]{0,20}$";

    
   
NSPredicate *prd = [NSPredicate
predicateWithFormat:@"SELF MATCHES %@", regex];
   
return [prd evaluateWithObject:result];

    
}