未将对象引用设置到对象的实例

Question

在controller中 public ActionResult Sousuo()
        {
            businessDataContext db = new businessDataContext();
            
            
            if (string.IsNullOrEmpty(Request.Form["Sousuo"]))
            {
                ViewData["empty"] = "无搜索字！";
                return View();
            }
            else
            {
                string Name = Request.Form["Sousuo"];
                //List<string> SQL = new List<string>();
                //var SQL = from c in db.Sousuo
                //          where c.Name.StartsWith("%Name%")
                //          select c;
                //ViewData["SQL"] = Name;                var SQL = db.Sousuo.Where(n => n.Name.StartsWith(Name) || n.Name.EndsWith(Name) || n.Name.IndexOf(Name) != -1);
                if (SQL.Equals("0"))
                {
                    ViewData["empty2"] = "无搜索结果";
                    return View();
                }
                else
                {                    ViewData["SQL"] = SQL;
                    return View(SQL);
                }
            }
在view中
<h2>Sousuo</h2>    <table>
        <tr>
            <th>
                Name
            </th>
        </tr>
    <%=ViewData["empty"]%>
    <%=ViewData["empty2"]%>
    
  <%foreach (string c in ViewData["SQL"] as List<string>)
    { %>
    
        <tr>
            <td>
                <%=c %>
            </td>
        </tr>   
    <% } %>
报错：“/”应用程序中的服务器错误。
--------------------------------------------------------------------------------未将对象引用设置到对象的实例。 
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。 异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误: 
行 18:     <%=ViewData["empty2"]%>
行 19:     
行 20:   <%foreach (string c in ViewData["SQL"] as List<string>)
行 21:     { %>
行 22:     
 
请教大虾，先谢了

Answer 1

ViewData["empty2"]==null?"":ViewData["empty2"]

Answer 2

 public ActionResult Sousuo()
  {
  businessDataContext db = new businessDataContext();
    
    
  if (string.IsNullOrEmpty(Request.Form["Sousuo"]))
  {
  ViewData["empty"] = "无搜索字！";
  return View();
  }
  else
  {
  ViewData["empty"]="";
  string Name = Request.Form["Sousuo"];
  //List<string> SQL = new List<string>();
  //var SQL = from c in db.Sousuo
  // where c.Name.StartsWith("%Name%")
  // select c;
  //ViewData["SQL"] = Name;  var SQL = db.Sousuo.Where(n => n.Name.StartsWith(Name) || n.Name.EndsWith(Name) || n.Name.IndexOf(Name) != -1);
  if (SQL.Equals("0"))
  {
  ViewData["empty2"] = "无搜索结果";
  return View();
  }
  else
  {
  ViewData["empty2"]="";
  ViewData["SQL"] = SQL;
  return View(SQL);
  }
  }

Answer 3

引用类型在调用前记得判断是否为null

Answer 4

谢谢各位  问题已解决
public ActionResult Sousuo()
        {
            businessDataContext db = new businessDataContext();
            
            if (Request.Form["Sousuo"].ToString().Length==0)
            {
                ViewData["empty"] = "无搜索字！请输入关键字后再搜索.";
       
                return View("Empty");
            }
            else 
            {
                string Name = Request.Form["Sousuo"];
                var SQL = db.News.Where(n => n.Title.Contains(Name));
                if (SQL==null)
                {
                    ViewData["empty2"] = "无搜索结果！";
                    return View("Empty");
                }
                else
                {
                    return View(SQL);                }
                
            }  <% foreach (var item in Model) { %>
    
        <tr>
           
            <td>
                <%= Html.ActionLink(item.Title, "content", new { id=item.NewsID }) %>
            </td>
            <td>
                <%= Html.Encode(item.Froms) %>
            </td>
            <td>
                <%= Html.Encode(String.Format("{0:g}", item.Time)) %>
            </td>
            <td>
                <%= Html.Encode(item.TypeName) %>
            </td>
        </tr>
    
    <% } %>