在此代码中，此文本更改方法是从更新面板触发器中调用的，我执行一些计算（即将gridview单元格值相加）并将计算结果存储在总变量中。然后将此总变量分配给txtTotalAmount文本框，但是成功执行代码后，此值在该文本框中不可见。
要获得帮助，请先感谢：
protected void txtProductPrice_TextChanged(object sender, EventArgs)
{
DataTable dt;
DataRow dr = null;
if (ViewState["CurrentData"] != null)
{
dt = (DataTable)ViewState["CurrentData"];
dr = dt.NewRow();
dr[0] = ddlProductName.SelectedItem.Value;
dr[1] = ddlProductName.SelectedItem.ToString();
dr[2] = txtQuantity.Text;
dr[3] = txtUnit.Text;
dr[4] = txtProductPrice.Text;
dr[5] = Convert.ToDouble(txtProductPrice.Text) * Convert.ToDouble(txtQuantity.Text);
dt.Rows.Add(dr);
}
else
{
dt = new DataTable();
dt.Columns.Add(new DataColumn("prcode", typeof(string)));//for TextBox value
dt.Columns.Add(new DataColumn("prname", typeof(string)));//for TextBox value
dt.Columns.Add(new DataColumn("qty", typeof(string)));//for TextBox value
dt.Columns.Add(new DataColumn("unit", typeof(string)));//for TextBox value
dt.Columns.Add(new DataColumn("price", typeof(string)));//for TextBox value
dt.Columns.Add(new DataColumn("total", typeof(string)));//for TextBox value
dr = dt.NewRow();
dr[0] = ddlProductName.SelectedItem.Value;
dr[1] = ddlProductName.SelectedItem.ToString();
dr[2] = txtQuantity.Text;
dr[3] = txtUnit.Text;
dr[4] = txtProductPrice.Text;
dr[5] = Convert.ToDouble(txtProductPrice.Text) * Convert.ToDouble(txtQuantity.Text);
dt.Rows.Add(dr);
}
grdSaleInvoice.DataSource = dt;
grdSaleInvoice.DataBind();
ViewState["CurrentData"] = dt;
double total = 0;
for (int i = 0; i < grdSaleInvoice.Rows.Count; i++)
{
total += Convert.ToDouble(((TextBox)grdSaleInvoice.Rows[i].Cells[4].FindControl("total")).Text);
}
txtTotalAmount.Text = total.ToString();
}
<%@ Page Title="" Language="C#" MasterPageFile="~/Site1.Master" AutoEventWireup="true" EnableEventValidation="true" CodeBehind="SaleInvoice.aspx.cs" Inherits="POS.SaleInvoice" %>
<asp:Content ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<div id="content-wrapper">
<div class="container-fluid">
<form runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<div class="form-row">
<div class="form-group col-md-4">
<label>Invoice No</label>
<asp:TextBox runat="server" ReadOnly="true" CssClass="form-control" ID="txtInvoiceNo" placeholder="Auto"></asp:TextBox>
</div>
<div class="form-group col-md-4">
<label>Invoice Type</label>
<asp:DropDownList runat="server" CssClass="form-control" ID="ddlInvoiceType" placeholder="Invoice Type">
<asp:ListItem Text="Invoice Type" Value="-1">Invoice Type</asp:ListItem>
<asp:ListItem Text="Credit" Value="1">Credit</asp:ListItem>
<asp:ListItem Text="Cash" Value="2">Cash</asp:ListItem>
</asp:DropDownList>
</div>
<div class="form-group col-md-4">
<label>Customer</label>
<asp:DropDownList runat="server" CssClass="form-control" ID="ddlCustomer" placeholder="Customer"></asp:DropDownList>
</div>
</div>
<div class="form-row">
<div class="form-group col-md-4">
<label>Invoice Date</label>
<asp:TextBox runat="server" CssClass="form-control" ID="dtInvoiceDate"></asp:TextBox>
</div>
<div class="form-group col-md-8">
<label>Remarks</label>
<asp:TextBox runat="server" CssClass="form-control" ID="txtRemarks" placeholder="Remarks"></asp:TextBox>
</div>
</div>
<div class="form-row" id="productData">
<div class="form-group col-md-2">
<label>Pr. Code</label>
<asp:TextBox runat="server" CssClass="form-control" EnableViewState="true" value="" AutoPostBack="true" ID="txtProductCode" placeholder="Code" OnTextChanged="txtProductCode_TextChanged"></asp:TextBox>
</div>
<div class="form-group col-md-2">
<label>Pr. Name</label>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:DropDownList runat="server" CssClass="form-control" value="" ID="ddlProductName" placeholder="Name" DataTextField="product_name" DataValueField="product_id"></asp:DropDownList>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="txtProductCode" EventName="TextChanged" />
</Triggers>
</asp:UpdatePanel>
</div>
<div class="form-group col-md-2">
<label>Quantity</label>
<asp:TextBox runat="server" CssClass="form-control" value="" ID="txtQuantity" placeholder="Quantity"></asp:TextBox>
</div>
<div class="form-group col-md-2">
<label>Unit</label>
<asp:TextBox runat="server" CssClass="form-control" ReadOnly="true" value="" ID="txtUnit" Text="Piece"></asp:TextBox>
</div>
<div class="form-group col-md-2">
<label>Price</label>
<asp:TextBox runat="server" CssClass="form-control" value="" ID="txtProductPrice" AutoPostBack="true" placeholder="Price" OnTextChanged="txtProductPrice_TextChanged"></asp:TextBox>
</div>
<div class="form-group col-md-2">
<label>Total</label>
<asp:TextBox runat="server" ReadOnly="true" CssClass="form-control" value="" ID="txtTotal" placeholder="Total"></asp:TextBox>
</div>
</div>
<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:GridView runat="server" ID="grdSaleInvoice" AutoGenerateColumns="False" BackColor="White" BorderColor="#CCCCCC" BorderStyle="None" BorderWidth="1px" CellPadding="4" GridLines="Horizontal" ForeColor="Black" Width="100%">
<Columns>
<asp:TemplateField HeaderText="Pr. Code">
<ItemTemplate>
<asp:TextBox runat="server" ID="prcode" Text='<%# Bind("prcode") %>' ReadOnly="false"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Pr. Name">
<ItemTemplate>
<asp:TextBox runat="server" ID="prname" Text='<%# Bind("prname") %>' ReadOnly="false"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Quantity">
<ItemTemplate>
<asp:TextBox runat="server" ID="qty" Text='<%# Bind("qty") %>' ReadOnly="false"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Unit">
<ItemTemplate>
<asp:TextBox runat="server" ID="unit" Text='<%# Bind("unit") %>' ReadOnly="false"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Price">
<ItemTemplate>
<asp:TextBox runat="server" ID="price" Text='<%# Bind("price") %>' ReadOnly="false"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Total">
<ItemTemplate>
<asp:TextBox runat="server" ID="total" Text='<%# Bind("total") %>' ReadOnly="false"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Delete">
<ItemTemplate>
<asp:LinkButton ID="btnDelete" runat="server" CssClass="btn btn-danger"><i class="material-icons" style="font-size:30px">delete</i></asp:LinkButton>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<FooterStyle BackColor="#CCCC99" ForeColor="Black" />
<HeaderStyle BackColor="#333333" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="White" ForeColor="Black" HorizontalAlign="Right" />
<SelectedRowStyle BackColor="#CC3333" Font-Bold="True" ForeColor="White" />
<SortedAscendingCellStyle BackColor="#F7F7F7" />
<SortedAscendingHeaderStyle BackColor="#4B4B4B" />
<SortedDescendingCellStyle BackColor="#E5E5E5" />
<SortedDescendingHeaderStyle BackColor="#242121" />
</asp:GridView>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="txtProductPrice" EventName="TextChanged" />
</Triggers>
</asp:UpdatePanel>
<div class="form-row">
<div class="form-group col-md-4">
<label>Discount</label>
<asp:TextBox ID="txtDiscount" CssClass="form-control" placeholder="Discount" runat="server"></asp:TextBox>
</div>
<div class="form-group col-md-4">
<label>Tax</label>
<asp:TextBox ID="txtTax" CssClass="form-control" placeholder="Tax" runat="server"></asp:TextBox>
</div>
<div class="form-group col-md-4">
<label>Total Amount</label>
<asp:TextBox ID="txtTotalAmount" EnableViewState="true" CssClass="form-control" placeholder="Total Amount" runat="server"></asp:TextBox>
</div>
</div>`enter code here`
<br />
<div class="form-row">
<div class="form-group col-md-3">
<asp:Button ID="btnSave" runat="server" CssClass="btn btn-success btn-group-lg" Text="Save" OnClick="btnSave_Click" />
<a href="ProductList.aspx" id="btnCancle" runat="server" class="btn btn-danger">Cancel</a>
</div>
</div>
</form>
</div>
</div>
</asp:Content>