数字键盘回收的问题－限制只能数字输入

- (BOOL)textField:(UITextField*)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString*)string{    NSCharacterSet*cs;    cs = [[NSCharacterSetcharacterSetWithCharactersInString:NUMBERS] invertedSet];    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];    BOOL basicTest = [string isEqualToString:filtered];    if(!basicTest) {        UIAlertView* alert = [[UIAlertViewalloc] initWithTitle:@"提示" message:@"请输入数字" delegate:nil cancelButtonTitle:@"确定" otherButtonTitles:nil]; [alert show]; return NO;    }    return YES;}