消息未重新更新

Question

我有2种＆＃34;描述＆＃34;对于班级＆＃34;人们＆＃34;，

1. 拥有Message：，Priority：和Tag：
的数据

2. 拥有没有这些的数据

   List<People> lstPeople = new List<People>
   {
       new People { Message = "[1y] Message: test messg1 Priority: top Tag: t1" },
       new People { Message = "without Message, Priority and Tag desc" }
   };
   var data = lstPeople;
   

我想在＆＃34;消息之后提取数据：＆＃34;，＆＃34;优先级：＆＃34;和＆＃34;标签：＆＃34;并重新更新＆＃34; People＆＃34;的每个实体。 class＆＃34; Message＆＃34;，＆＃34; Priority＆＃34;和＆＃34;标记＆＃34;。

以下代码更新了＆＃34;优先级＆＃34;和＃34;标记＆＃34;但不是＆＃34;消息＆＃34;。可能是什么原因？

    public class People
{
    const string ALERT_DESC_MARKER = "Message:";
    const string PRIORITY_MARKER = "Priority:";
    const string TAG_MARKER = "Tag:";
    private string _description;
    private string _tag;
    private string _priority;
    public string Message
    {
        get
        {
            if (_description.Contains(ALERT_DESC_MARKER) && _description.Contains(PRIORITY_MARKER))
                return _description ?? GetTextPart(_description, ALERT_DESC_MARKER, PRIORITY_MARKER).Trim();
            else
                return _description;
        }
        set
        {
            _description = value;
        }
    }

    public string Priority
    {
        get
        {
            if (_description.Contains(PRIORITY_MARKER) && _description.Contains(TAG_MARKER))
                return _priority = GetTextPart(_description, PRIORITY_MARKER, TAG_MARKER).Trim();
            else
                return _priority;
        }
        set
        {
            _priority = value;
        }
    }

    public string Tag
    {
        get
        {
            if (_description.Contains(TAG_MARKER))
                return _tag = GetTextPart(_description, TAG_MARKER, null).Trim();
            else
                return _tag;
        }
        set
        {
            _tag = value;
        }
    }

    private string GetTextPart(string text, string before, string after)
    {
        string result = null;
        int posBefore = text.IndexOf(before);

        if (after != null)
        {
            int posAfter = text.IndexOf(after);
            result = text.Remove(posAfter).Substring(posBefore + before.Length).TrimEnd();
        }
        else
            result = text.Substring(posBefore + before.Length);

        return result;
    }
}

Answer 1

问题在于Message的吸气者。 正如documentation所说：

  

?? operator被称为null-coalescing运算符。如果操作数不为null，则返回左侧操作数;否则它返回右手操作数。

因此，如果string不是_description，那么您总是会返回整个null。相反，如果满足此条件（_decription！= null），则需要返回GetTextPart。像这样：

if (_description.Contains(ALERT_DESC_MARKER) && _description.Contains(PRIORITY_MARKER))
    return _description != null ? GetTextPart(_description, ALERT_DESC_MARKER, PRIORITY_MARKER).Trim() : _description;

修改

以下是您的测试示例：

List<People> lstPeople = new List<People>
{
    new People { Message = "[1y] Message: test messg1 Priority: top Tag: t1" },
    new People { Message = "without Message, Priority and Tag desc" }
};
var data = lstPeople;


foreach (var item in lstPeople)
{
    Console.WriteLine(item.Message);
    Console.WriteLine(item.Priority);
    Console.WriteLine(item.Tag);
}

输出第一项：

  

测试messg1

     

顶

     

T1

输出第二项：

  

没有消息，优先级和标记desc

第二项Priority中的

和Tag为空。

编辑2：

这是Message吸气剂。我以前测试的其余代码与您发布的代码相同。注释掉的部分是您的旧/已发布版本

public string Message
{
    get
    {
        if (_description.Contains(ALERT_DESC_MARKER) && _description.Contains(PRIORITY_MARKER))
            return _description != null ? GetTextPart(_description, ALERT_DESC_MARKER, PRIORITY_MARKER).Trim(): _description;

        //if (_description.Contains(ALERT_DESC_MARKER) && _description.Contains(PRIORITY_MARKER))
        //    return _description ?? GetTextPart(_description, ALERT_DESC_MARKER, PRIORITY_MARKER).Trim();
        else
            return _description;
    }
    set
    {
        _description = value;
    }
}