C# XML 驅動的 ASP.NET 控件輸入長度限制元件（一）：核心解析邏輯與結構體定義

結構體定義

public struct strRestric
{
    public string msgPage;    // 頁面顯示訊息
    public string msgPrompt;  // 提示訊息
    public int size;          // 最大長度
}

核心解析類別

public class XMLRestrict
{
    public static strRestric res;

    public XMLRestrict()
    {
        res.msgPage = "";
        res.msgPrompt = "";
        res.size = 0;
    }

    public static object Restrict(string XMLPathName, string nodeID, strRestric res)
    {
        int NodeNum = 1;
        string path = ConfigurationSettings.AppSettings[XMLPathName].ToString();
        path += "Restrict.xml";

        try
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(path);
            XmlNodeList nodeList = xmlDoc.SelectSingleNode("Tree").ChildNodes;

            foreach (XmlNode xn in nodeList)
            {
                XmlElement xe = (XmlElement)xn;
                if (xe.Name == "Node")
                {
                    XmlNodeList nls = xe.ChildNodes;
                    foreach (XmlNode xn1 in nls)
                    {
                        XmlElement xe2 = (XmlElement)xn1;
                        if (xe2.Name == "PageId" && xe2.InnerText == nodeID)
                        {
                            XmlNode xnChild = (XmlNode)xe2;
                            XmlNode child = xnChild.ParentNode.ChildNodes[NodeNum + 1];
                            XmlElement xeChild = (XmlElement)child;
                            string Id = xeChild.GetAttribute("value");
                            int Pid = int.Parse(Id);
                            res.msgPage = child.InnerText.ToString();
                            res.msgPrompt = xnChild.ParentNode.ChildNodes[NodeNum + 2].InnerText.ToString();
                            res.size = Pid;
                            return res;
                        }
                        break;
                    }
                }
            }
        }
        catch { }
        return null;
    }
}

邏輯流程分析

1. 從 AppSettings 讀取基礎路徑，拼接檔案名
2. 載入 XML，取得 <Tree> 直系子節點
3. 遍歷每個 <Node>，尋找 <PageId> 匹配
4. 匹配成功後，透過固定索引取得同層級後續節點（Control、Message）
5. 解析屬性與內容填充結構體

關鍵缺陷與風險

重構版本草案

public sealed class InputLengthResolver
{
    private readonly Dictionary _cache = new();
    private readonly string _xmlPath;

    public InputLengthResolver(string xmlPath) => _xmlPath = xmlPath;

    public InputRule Resolve(string controlId)
    {
        if (_cache.TryGetValue(controlId, out var rule)) return rule;

        var doc = XDocument.Load(_xmlPath);
        var element = doc.XPathSelectElement($"/Tree/Node[PageId='{controlId}']");
        if (element == null) return InputRule.Default;

        rule = new InputRule
        {
            MaxLength = (int)element.Element("Control").Attribute("value"),
            PageMessage = (string)element.Element("Message"),
            PromptMessage = (string)element.Element("Prompt") // 假設新增
        };
        _cache[controlId] = rule;
        return rule;
    }
}

public struct InputRule
{
    public int MaxLength;
    public string PageMessage;
    public string PromptMessage;
    public static InputRule Default => new InputRule { MaxLength = int.MaxValue };
}