【发布时间】：2017-02-20 14:01:35
【问题描述】：
我正在开发一个用于管理学生考试条目的 Web 应用程序，但我的 gridview 遇到了问题。
基本理念是用户可以继续输入和更新学生考试的详细信息。当某些主题需要填充不同的字段时，就会出现并发症，这就是我的问题所在。
运行保存按钮方法时引发异常。运行 AddAudit 和 UpdateRecord 方法时，我得到一个空对象引用。在从外观上进行一些调试之后，问题是没有从 gridview 的 FindCotrol 方法声明控件（ddlDate、txtAssesmentLevel 等），这意味着当调用 AddAudit 和 UpdateRecord 方法时它们指向一个空控制器。
请注意，当代码不是“C2555”时不会发生此问题，这使我怀疑问题在于动态添加列和控件变得混乱，尽管我不确定。
任何帮助都会很棒，请随时询问更多信息。
下面是我的基本代码：
页面加载方法
protected void Page_Load(object sender, EventArgs e){
if(!IsPostBack){
//Selected class passed through
selectedClass sc = (selectedClass)Session["selectedClass"] as selectedClass;
//Get Class Code
lblAosCode.Text = sc.getAOSCode();
//If class is English
if(lblAosCode.Text == "C2555"){
TemplateField speakingListening = new TemplateField();
speakingListening.HeaderText = "Speaking and Listening";
dgvSelectedClasses.Columns.Insert(7, speakingListening);
}
//Populate Gridview
DataTable dsSelectedClasses = AccessData.getSelectedClasses(sc.getAOSCode(), sc.getAOSPeriod(), sc.getDescription());
dgvSelectedClasses.DataSource = dsSelectedClasses;
dgvSelectedClasses.DataBind();
//Check if txtAssesmentLevel is populated
for (int index = 0; index < dgvSelectedClasses.Rows.Count; index++)
{
TextBox txtAssessmentLevel = (TextBox)dgvSelectedClasses.Rows[index].FindControl("txtAssessmentLevel");
if (dgvBefore.Rows[index].Cells[4].Text != " ")
{
txtAssessmentLevel.ReadOnly = true;
}
}
}
}
保存方法（抛出异常）
protected void btnSave_Click(object sender, EventArgs e)
{
for (int i = 0; i < dgvSelectedClasses.Rows.Count; i++)
{
DropDownList ddlL1L2 = (DropDownList)dgvSelectedClasses.Rows[i].FindControl("ddlL1L2");
DropDownList ddlExamDate = (DropDownList)dgvSelectedClasses.Rows[i].FindControl("ddlExamDate");
TextBox txtAssessmentLevel = (TextBox)dgvSelectedClasses.Rows[i].FindControl("txtAssessmentLevel");
DropDownList ddlSpeakingListening = null;
if (lblAosCode.Text.Contains("C2555"))
{
ddlSpeakingListening = (DropDownList)dgvSelectedClasses.Rows[i].FindControl("ddlSpeakingListening");
}
if (IsPostBack)
{
if (lblAosCode.Text.Contains("C2555"))
{
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Assessment Level", txtAssessmentLevel.Text, dgvBefore.Rows[i].Cells[4].Text);
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Exam request L1 or L2", ddlL1L2.SelectedValue, dgvBefore.Rows[i].Cells[14].Text);
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Exam Date", ddlExamDate.SelectedValue, dgvBefore.Rows[i].Cells[15].Text);
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Speaking and Listening", ddlSpeakingListening.SelectedValue, dgvBefore.Rows[i].Cells[7].Text);
AccessData.updateRecord(txtAssessmentLevel.Text, ddlL1L2.SelectedValue, ddlExamDate.SelectedValue, lblAosCode.Text, lblAosPeriod.Text, dgvSelectedClasses.Rows[i].Cells[0].Text, ddlSpeakingListening.SelectedValue);
}
else
{
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Assessment Level", txtAssessmentLevel.Text, dgvBefore.Rows[i].Cells[4].Text);
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Exam request L1 or L2", ddlL1L2.SelectedValue, dgvBefore.Rows[i].Cells[13].Text);
AccessData.addAudit(dgvSelectedClasses.Rows[i].Cells[0].Text, Context.User.Identity.Name, "Exam Date", ddlExamDate.SelectedValue, dgvBefore.Rows[i].Cells[14].Text);
AccessData.updateRecord(txtAssessmentLevel.Text, ddlL1L2.SelectedValue, ddlExamDate.SelectedValue, lblAosCode.Text, lblAosPeriod.Text, dgvSelectedClasses.Rows[i].Cells[0].Text);
}
}
}
Response.Redirect("~/contact");
}
行数据绑定
protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
if (lblAosCode.Text.Contains("C2555"))
{
DropDownList ddlSpeakingListening = new DropDownList();
ddlSpeakingListening.ID = "ddlSpeakingListening";
ddlSpeakingListening.Items.Add("L1");
ddlSpeakingListening.Items.Add("L2");
ddlSpeakingListening.Items.Add("Entry");
ddlSpeakingListening.Items.Add("NS");
e.Row.Cells[7].Controls.Add(ddlSpeakingListening);
}
}
}
ASP.NET
<asp:GridView ID="dgvSelectedClasses" runat="server" AutoGenerateColumns="False" OnRowDataBound="OnRowDataBound">
<Columns>
<asp:BoundField DataField="StudentID" HeaderText="Student ID" ReadOnly="True" />
<asp:BoundField DataField="StageCode" HeaderText="Stage Code" ReadOnly="True" />
<asp:BoundField DataField="Forename" HeaderText="Forename" ReadOnly="True" />
<asp:BoundField HeaderText="Surname" DataField="Surname" />
<asp:TemplateField HeaderText="Assessment Level">
<ItemTemplate>
<asp:TextBox ID="txtAssessmentLevel" Text ='<%#Bind("AssessmetLevel") %>' runat="server" Width="50px"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="TargetLevel" HeaderText="Target Level" />
<asp:BoundField DataField="Achievelevel" HeaderText="Achieve Level" />
<asp:BoundField DataField="FELSOutcome" HeaderText="FELS Outcome" />
<asp:BoundField DataField="Registration" HeaderText="Registration" />
<asp:BoundField DataField="DateSpreadsheetSent" HeaderText="Last Update" />
<asp:BoundField DataField="Dayofclass" HeaderText="Day of class" />
<asp:BoundField DataField="Timeofclass" HeaderText="Time of class" />
<asp:BoundField DataField="Location" HeaderText="Location" />
<asp:TemplateField HeaderText="Exam request L1 or L2" >
<ItemTemplate>
<asp:DropDownList ID="ddlL1L2" runat="server" >
<asp:ListItem>Not Set</asp:ListItem>
<asp:ListItem>L1</asp:ListItem>
<asp:ListItem>L2</asp:ListItem>
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Exam date">
<ItemTemplate>
<asp:DropDownList ID="ddlExamDate" runat="server">
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
<asp:GridView ID="dgvBefore" runat="server" AutoGenerateColumns="False">
<Columns>
<asp:BoundField DataField="StudentID" HeaderText="Student ID" ReadOnly="True" />
<asp:BoundField DataField="StageCode" HeaderText="Stage Code" ReadOnly="True" />
<asp:BoundField DataField="Forename" HeaderText="Forename" ReadOnly="True" />
<asp:BoundField HeaderText="Surname" DataField="Surname" />
<asp:BoundField DataField="AssessmetLevel" HeaderText="Assessment Level" NullDisplayText=" "/>
<asp:BoundField DataField="TargetLevel" HeaderText="Target Level" />
<asp:BoundField DataField="AchieveLevel" HeaderText="Achieve Level" />
<asp:BoundField DataField="FELSOutcome" HeaderText="FELS Outcome" />
<asp:BoundField DataField="Registration" HeaderText="Registration" />
<asp:BoundField DataField="DateSpreadsheetSent" HeaderText="Date Spreadsheet Sent" />
<asp:BoundField DataField="Dayofclass" HeaderText="Day of class" />
<asp:BoundField DataField="Timeofclass" HeaderText="Time of class" />
<asp:BoundField DataField="Location" HeaderText="Location" />
<asp:BoundField DataField="ExamrequestL1orL2" HeaderText="Exam request L1 or L2" />
<asp:BoundField DataField="Examdate" HeaderText="Exam date" />
<asp:BoundField DataField="Reviewed" HeaderText="Reviewed" />
</Columns>
</asp:GridView>
附：这是我的第一个问题，希望它是有道理的，我愿意接受指点:)
编辑：页面加载方法确实包含填充 dgvBefore 的代码以及一些我刚刚忘记包含它的身份验证内容。
【问题讨论】：
-
James，虽然您粘贴了很多代码，但问题并不清楚。你能用确切的问题陈述更新它吗？
-
@A3006 问题是当我按下保存按钮时，会抛出空对象引用异常。我在保存方法开始时使用查找控件方法的地方没有分配来自网格视图的控件。该错误仅在添加新的“ddlSpeakingListening”列时发生。