0

摘要：我正在构建一个应用程序功能来报告丢失的数据。缺少记录的不同名称填充我的下拉列表。但是，当我开始按该特定名称（或任何名称）搜索完整报告时，出现此错误以及应用程序崩溃：

错误：用户代码未处理 NullReferenceException。
你调用的对象是空的。

我的视图（错误所在的位置）：

看法：

@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();
        }

模型：

    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;
        }
    }

任何和所有的帮助将不胜感激！

4

1 回答 1

0

首先，您的“主页”控制器中是否有一个名为“索引”的发布操作，它接收带有表单中字段的模型？

我会使用 DropDownListFor 方法，而不是 ViewData 方法，而不是按照你的方式。因此，在您的控制器中，SelectList使用您从中获得的字符串列表创建一个MissingQueryResults().

注：代码未经测试，直接写在这里。

模型 创建一个包含您需要传递的所有数据和发布到控制器操作的视图模型：

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);
}

在您看来：

@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)
}
于 2013-04-24T21:25:08.693 回答