DropDownList VS.在HTML.Beginform上提交/搜索

Question

摘要：我构建了一个应用程序功能来报告缺失的数据。缺少记录的不同名称会填充我的下拉列表。但是，当我开始通过该特定名称（或任何名称）搜索完整报告时，出现此错误以及应用崩溃：

错误：NullReferenceException未被用户代码处理。
对象引用未设置为对象的实例。

我的视图（错误所在位置）：

VIEW：

@using (Html.BeginForm("Index", "Home", "POST")) 
{ 
    <div class="searchField"> 
     <input type="text" class="search-query" name="heatSearch" placeholder="Search"> 
     <button class="btn btn-success" type="submit">Search</button> 
    </div> 
    <br /> 
    <select> 
    @foreach (var item in (ViewData["MissingChem"] as IEnumerable<string>)) 
    { 
     <option> @item </option> 
    } 

    </select> 
} 

控制器：

public ActionResult Index() 
     { 
      Session["InitialLoad"] = "Yes"; 
      HomeModel H = new HomeModel(); 
      ViewData["MissingChem"] = H.MissingQueryResults(); 
      return View(); 
     } 

型号：

public List<string> MissingQueryResults() 
     { 
      //HomeModel Tolerances = new HomeModel(); 
      List<String> nameList = new List<String>(); 

      SqlCommand missingQuery = new SqlCommand("SELECT heatname FROM dbo.chemistrytable WHERE heatname NOT IN (SELECT heatname FROM dbo.chemistrytable WHERE sampletype = 'AVE') AND analysistime between '01-01-2013' and Current_Timestamp AND heatname LIKE '[a,b,c,d]%' Order by heatname");// + heatName + "'"); 
      SqlCommand mainquery = new SqlCommand("SELECT analysisv 

alue.analysisid, heatname, analysistime, sampletype, grade, productid, element, value FROM dbo.AnalysisValue INNER JOIN dbo.ChemistryAnalysis ON dbo.AnalysisValue.AnalysisID = dbo.ChemistryAnalysis.AnalysisID Where heatname = '" + "' Order By analysisvalue.analysisid Asc, element"); 

     using (SqlConnection conn = new SqlConnection(strSQLconnection)) 
     { 
      missingQuery.CommandTimeout = 20000;//Dateadd(day, -1, Current_Timestamp) 
      conn.Open(); 
      missingQuery.Connection = new SqlConnection(strSQLconnection); 
      missingQuery.Connection.Open(); 

      using (var reader = missingQuery.ExecuteReader()) 
      { 
       int fieldCount = reader.FieldCount; 

       while (reader.Read()) 
       { 
        for (int i = 0; i < fieldCount; i++) 
        { 
         nameList.Add(reader[i].ToString().Trim()); 

        } 

       } 
      }return nameList; 
     } 
    } 

任何和所有帮助会不胜感激！

Answer 1

首先，您是否在您的“Home”控制器中有一个名为“Index”的发布操作，该操作接收带有表单中字段的模型？

我会用DropDownListFor方法，而不是ViewData方法，而不是像你这样做。 因此，在您的控制器中，使用您从MissingQueryResults()获取的字符串列表创建SelectList。

注：代码没有经过测试，直接写在这里。

public class VMHome { 
public SelectList MissingQueryResults {get; set;} // to build the dropdownList 
public string heatSearch {get; set;} 
public string MissingItem {get; set;} //for posting selected value 

} 

控制器

public ActionResult Index() 
{ 
      Session["InitialLoad"] = "Yes"; 
      VMHome h = new VMHome(); 
      h.heatSearch = ""; 
      h.MissingQueryResults = new SelectList(H.MissingQueryResults()) 
      return View(h); 
} 
[HttpPost] 
public ActionResult Index(VMHome model) 
{ 
      //do something with your posted data 
      // may be adding search result to the viewmodel 
      return View(model); 
} 

您认为：

型号 你需要传递的所有数据和控制器动作后创建一个视图模型

@model VMHome 
@using (Html.BeginForm("Index", "Home", "POST")) 
{ 
    <div class="searchField"> 
     @Html.TextBoxFor(x => x.heatSearch, new {placeholder = "Search", class = "search-query"}) 
     <button class="btn btn-success" type="submit">Search</button> 
    </div> 
    <br /> 
    @Html.DropDownListFor(x => x.MissingItem, Model.MissingQueryResults) 
}