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[英]JSON to GridView parsing | System.NullReferenceException
[英]'System.NullReferenceException' on control in footer row of gridview
我正在嘗試在網格視圖的頁腳行中填充一個下拉列表。 我的標記如下:
<asp:Label ID="lblGrdImages" runat="server" ></asp:Label>
<asp:GridView
ID="grdImages"
runat="server"
AllowPaging="true"
ShowFooter="true"
PageSize="5"
AutoGenerateColumns="false"
OnPageIndexChanging="grdImages_PageIndexChanging"
OnRowCancelingEdit="grdImages_RowCancelingEdit"
OnRowCommand="grdImages_RowCommand"
OnRowEditing="grdImages_RowEditing"
OnRowUpdating="grdImages_RowUpdating"
OnRowDeleting="grdImages_RowDeleting"
EmptyDataText="No Data Available at this Time" >
<AlternatingRowStyle BackColor="White" ForeColor="#284775"></AlternatingRowStyle>
<Columns>
<asp:TemplateField AccessibleHeaderText="Product ID" HeaderText="Product ID" FooterText="Product ID">
<ItemTemplate>
<asp:Label ID="lblProdId" runat="server" Text='<%# Eval("pi.ProductId") %>' ></asp:Label>
</ItemTemplate>
<EditItemTemplate>
<asp:Label ID="lblEditProdId" runat="server" Text='<%# Eval("pi.ProductId") %>' ></asp:Label>
</EditItemTemplate>
<FooterTemplate>
<asp:DropDownList ID="lstAddProdId" runat="server" AppendDataBoundItems="true" >
<asp:ListItem>Select a product</asp:ListItem>
</asp:DropDownList>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField AccessibleHeaderText="Product Main Image" FooterText="Product Main Image" HeaderText="Product Main Image">
<ItemTemplate>
<asp:Label ID="lblMainImgId" runat="server" Text='<%# Eval("pi.ImageId") %>' ></asp:Label>
<asp:Image ID="imgMain" runat="server" Height="250" Width="250" ImageUrl='<%# Eval("pi.ImagePath") %>' />
</ItemTemplate>
<FooterTemplate>
<asp:FileUpload ID="flupMain" runat="server" AllowMultiple="false" />
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField AccessibleHeaderText="Supporting Images" FooterText="Supporting Images" HeaderText="Supporting Images">
<ItemTemplate>
<h2>repeater here</h2>
</ItemTemplate>
<FooterTemplate>
<asp:FileUpload ID="flupExtra" runat="server" AllowMultiple="true" />
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Edit">
<ItemTemplate>
<asp:LinkButton ID="btnEdit" Text="Edit" runat="server" CommandName="Edit" />
<br />
<span onclick="return confirm('Are you sure you want to declare this product Discontinued?')">
<asp:LinkButton ID="btnDelete" Text="Delete" runat="server" CommandName="Delete" />
</span>
</ItemTemplate>
<EditItemTemplate>
<asp:LinkButton ID="btnUpdate" Text="Update" runat="server" CommandName="Update" />
<br />
<asp:LinkButton ID="btnCancel" Text="Cancel" runat="server" CommandName="Cancel" />
</EditItemTemplate>
<FooterTemplate>
<asp:Button ID="btnAddRecord" runat="server" Text="Add" CommandName="Add"></asp:Button>
</FooterTemplate>
</asp:TemplateField>
</Columns>
<EditRowStyle BackColor="#999999"></EditRowStyle>
<FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White"></FooterStyle>
<HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White"></HeaderStyle>
<PagerStyle HorizontalAlign="Center" BackColor="#284775" ForeColor="White"></PagerStyle>
<RowStyle BackColor="#F7F6F3" ForeColor="#333333"></RowStyle>
<SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333"></SelectedRowStyle>
<SortedAscendingCellStyle BackColor="#E9E7E2"></SortedAscendingCellStyle>
<SortedAscendingHeaderStyle BackColor="#506C8C"></SortedAscendingHeaderStyle>
<SortedDescendingCellStyle BackColor="#FFFDF8"></SortedDescendingCellStyle>
<SortedDescendingHeaderStyle BackColor="#6F8DAE"></SortedDescendingHeaderStyle>
</asp:GridView>
我的代碼后面的函數用於填充下拉列表:
protected void lstProducts()
{
// find dropdownlist in the footer row of the gridview
DropDownList prods = (DropDownList)grdImages.FooterRow.FindControl("lstAddProdId");
// define ado.net objects
SqlConnection con = new SqlConnection(connectionString);
SqlCommand cmd = new SqlCommand("ProductDetails.bnc_ProductImages", con);
cmd.CommandType = CommandType.StoredProcedure;
SqlDataReader reader;
// define the sp parameters
cmd.Parameters.Add(new SqlParameter("@Status", SqlDbType.VarChar, 50));
cmd.Parameters["@Status"].Value = "LstProds";
try
{
con.Open(); // try to connect to db.
reader = cmd.ExecuteReader(); // execut the reader
while (reader.Read())
{
ListItem item = new ListItem(); // create listitem
item.Text = reader["p.ProductName"].ToString(); // add product name to item text
item.Value = reader["p.ProductId"].ToString(); // add productId to item value
prods.Items.Add(item); // populate dropdown list.
}
}
catch (Exception err)
{
lblGrdImages.Text = err.Message; // display error message in a label
}
finally
{
con.Close(); // close the connection.
}
}
當我嘗試運行它時,出現以下錯誤:
App_Web_su5rfbqf.dll中發生類型為'System.NullReferenceException'的異常,但未在用戶代碼中處理
我不確定為什么會收到這個例外。 我假設它無法在網格視圖頁腳行中找到控件,但我不知道為什么。 在某處可能是一個愚蠢的錯誤,但我不知道該怎么辦
編輯我在lstProducts()的這一行上收到錯誤:
DropDownList prods = (DropDownList)grdImages.FooterRow.FindControl("lstAddProdId");
您必須grdImages.FooterRow=null
Datasource
設置為grdImages.FooterRow=null
您遇到的錯誤是在grdImages.FooterRow=null
。嘗試先填充grdImages
然后嘗試訪問它。
這是一個類似的例子
<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
runat="server" AutoGenerateColumns="false" ShowFooter = "true" OnDataBound = "OnDataBound">
<Columns>
<asp:TemplateField HeaderText = "Name">
<ItemTemplate>
<asp:Label ID="lblName" runat="server" Text='<%# Eval("Name") %>' />
</ItemTemplate>
<FooterTemplate>
<asp:TextBox ID="txtName" runat="server" />
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText = "Country">
<ItemTemplate>
<asp:Label ID="lblName" runat="server" Text='<%# Eval("Country") %>' />
</ItemTemplate>
<FooterTemplate>
<asp:DropDownList ID="ddlCountries" runat="server">
</asp:DropDownList>
</FooterTemplate>
</asp:TemplateField>
</Columns>
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
DataTable dt = new DataTable();
dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id"), new DataColumn("Name"), new DataColumn("Country") });
dt.Rows.Add(1, "John Hammond", "United States");
dt.Rows.Add(2, "Mudassar Khan", "India");
dt.Rows.Add(3, "Suzanne Mathews", "France");
dt.Rows.Add(4, "Robert Schidner", "Russia");
GridView1.DataSource = dt;
GridView1.DataBind();
}
}
protected void OnDataBound(object sender, EventArgs e)
{
DropDownList ddlCountries = GridView1.FooterRow.FindControl("ddlCountries") as DropDownList;
}
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