Question

摘要：我正在构建一个报告缺失数据的应用程序功能。带有缺失记录的不同名称会填充我的下拉列表。但是，当我开始按特定名称（或任何名称）搜索完整报告时，我发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。

我的观点（错误所在的位置）：

查看：

@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;
        }
    }

任何和所有帮助将不胜感激！

Answer 1

首先，您的“Home”控制器中是否有一个名为“Index”的帖子操作，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，而不是像你那样。因此，在您的控制器中，使用从SelectList获得的字符串列表创建MissingQueryResults()。

注意：代码未经过测试，直接写在这里。

<强>模型创建一个viewModel，其中包含您需要传递的所有数据以及post to controller操作：

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

}

<强>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)
}

DropDownList VS.在HTML.Beginform上提交/搜索

1 个答案: