设置textview的delegate并实现此方法, 当有文本替换时, 判断是否为回车符, 为回车则输入无效

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
    if ([text isEqualToString:@"\n"]) {
        return NO;
    }
    return YES;
}