Object reference not set to an instance of an object

Question

User458524405 posted

Using Visual Studio 2012 ASP .NET 4.5 with C#

0x800a139e - JavaScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: Object reference not set to an instance of an object.

I'm receiving the above error for my shopping cart application and am not sure why.  Below are the page, code behind and class files.  Any Help would be greatly appreciated.

The particular line I'm receiving the error on is below, which is located in the Order.aspx.cs code behind file. 

• OrderItem orderItem = order[selectedItem.ProductID];

Order.aspx

<%

@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Order.aspx.cs" Inherits="Order" %>

<

asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">

<title>Mike's Shoes - Order</title>

<link rel="stylesheet" href="App_Themes/blueprint/screen.css" type="text/css" media="screen, projection" />

<link href="App_Themes/Blueprint/print.css" rel="stylesheet" type="text/css" media="print" />

<!--[if lt IE 8]>

<link href="App_Themes/Blueprint/ie.css" rel="stylesheet" type="text/css" media="screen, projection" />

<![endif]-->

<link rel="stylesheet" href="App_Themes/blueprint/StyleSheet.css" type="text/css" />

</

asp:Content>

<

asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">

<div class="content">

<%

--AJAX Update Panel--%>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">

<Triggers>

<asp:AsyncPostBackTrigger ControlID="ddlProductType" EventName="SelectedIndexChanged"/>

<asp:AsyncPostBackTrigger ControlID="ddlProductColor" EventName="SelectedIndexChanged"/>

<asp:AsyncPostBackTrigger ControlID="ddlProductSize" EventName="SelectedIndexChanged"/>

<asp:AsyncPostBackTrigger ControlID="gwProductList" EventName="SelectedIndexChanged" />

</Triggers>

<ContentTemplate>

<%

--Product Type Drop Down Menu--%>

<asp:DropDownList ID="ddlProductType" runat="server" DataSourceID="SqlDataSource1" DataTextField="ProductType" DataValueField="ProductType" OnSelectedIndexChanged="ddlProductType_SelectedIndexChanged" AutoPostBack="True"></asp:DropDownList>

<asp:SqlDataSource runat="server" ID="SqlDataSource1" ConnectionString='<%$ ConnectionStrings:ConnectionString %>' SelectCommand="SELECT DISTINCT [ProductType] FROM [tblProducts]"></asp:SqlDataSource>

<%

--Product Color Drop Down Menu--%>

<asp:DropDownList ID="ddlProductColor" runat="server" DataSourceID="SqlDataSource3" DataTextField="ProductColor" DataValueField="ProductColor" AutoPostBack="True" OnSelectedIndexChanged="ddlProductColor_SelectedIndexChanged"></asp:DropDownList>

<asp:SqlDataSource runat="server" ID="SqlDataSource3" ConnectionString='<%$ ConnectionStrings:ConnectionString %>' SelectCommand="SELECT DISTINCT [ProductColor] FROM [tblProducts]"></asp:SqlDataSource>

<%

--Product Size Drop Down Menu--%>

<asp:DropDownList ID="ddlProductSize" runat="server" DataSourceID="SqlDataSource4" DataTextField="ProductSize" DataValueField="ProductSize" OnSelectedIndexChanged="ddlProductSize_SelectedIndexChanged" AutoPostBack="True"></asp:DropDownList>

<asp:SqlDataSource runat="server" ID="SqlDataSource4" ConnectionString='<%$ ConnectionStrings:ConnectionString %>' SelectCommand="SELECT DISTINCT [ProductSize] FROM [tblProducts]"></asp:SqlDataSource>

<%

-- Gridview--%>

<asp:GridView ID="gwProductList" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource2" DataKeyNames="ProductID,ProductImage" OnSelectedIndexChanged="gwProductList_SelectedIndexChanged" SelectedIndex="1" SelectedRowStyle-Font-Bold="True">

<Columns>

<asp:BoundField DataField="ProductID" SortExpression="ProductID" Visible="False"></asp:BoundField>

<asp:BoundField DataField="ProductName" HeaderText="ProductName" SortExpression="ProductName"></asp:BoundField>

<asp:BoundField DataField="ProductType" HeaderText="ProductType" SortExpression="ProductType"></asp:BoundField>

<asp:BoundField DataField="ProductColor" HeaderText="ProductColor" SortExpression="ProductColor"></asp:BoundField>

<asp:BoundField DataField="ProductSize" HeaderText="ProductSize" SortExpression="ProductSize"></asp:BoundField>

<asp:BoundField DataField="ProductPrice" HeaderText="ProductPrice" SortExpression="ProductPrice"></asp:BoundField>

<asp:BoundField DataField="ProductImage" HeaderText="ProductImage" SortExpression="ProductImage" Visible="False"></asp:BoundField>

<asp:CommandField ShowSelectButton="True" ButtonType="Button" SelectText="Select" />

</Columns>

</asp:GridView>

<asp:SqlDataSource runat="server" ID="SqlDataSource2" ConnectionString='<%$ ConnectionStrings:ConnectionString %>' SelectCommand="SELECT * FROM [tblProducts] WHERE (([ProductType] = @ProductType) AND ([ProductColor] = @ProductColor) AND ([ProductSize] = @ProductSize))">

<SelectParameters>

<asp:ControlParameter ControlID="ddlProductType" PropertyName="SelectedValue" Name="ProductType" Type="String"></asp:ControlParameter>

<asp:ControlParameter ControlID="ddlProductColor" PropertyName="SelectedValue" Name="ProductColor" Type="String"></asp:ControlParameter>

<asp:ControlParameter ControlID="ddlProductSize" PropertyName="SelectedValue" Name="ProductSize" Type="Int32"></asp:ControlParameter>

</SelectParameters>

</asp:SqlDataSource>

<%

--Product Image Displayed When Selected--%>

<asp:Image ID="imgProduct" runat="server" />

<asp:Label ID="lblQuantity" runat="server" Text="Quantity"></asp:Label>

<asp:TextBox ID="txtQuantity" runat="server"></asp:TextBox>

<asp:Button ID="btnAdd" runat="server" Text="Add to Cart" OnClick="btnAdd_Click" />

<asp:Button ID="btnCart" runat="server" Text="Go to Cart" />

<asp:Button ID="btnCheckOut" runat="server" Text="Checkout" />

</ContentTemplate>

</asp:UpdatePanel>

</div>

</

asp:Content>

Order.aspx.cs

using

System;

using

System.Collections.Generic;

using

System.Linq;

using

System.Web;

using

System.Web.UI;

using

System.Web.UI.WebControls;

public

partial class Order : System.Web.UI.Page

{

private Product selectedItem;

protected void Page_Load(object sender, EventArgs e)

{

UnobtrusiveValidationMode = System.Web.UI.

UnobtrusiveValidationMode.None;

//GridViewRow selectRow = gwProductList.SelectedRow;

//selectedItem = this.GetSelectedItem();

}

protected void ddlProductType_SelectedIndexChanged(object sender, EventArgs e)

{

imgProduct.ImageUrl =

"";

}

protected void ddlProductColor_SelectedIndexChanged(object sender, EventArgs e)

{

imgProduct.ImageUrl =

"";

}

protected void ddlProductSize_SelectedIndexChanged(object sender, EventArgs e)

{

imgProduct.ImageUrl =

"";

}

protected void gwProductList_SelectedIndexChanged(object sender, EventArgs e)

{

imgProduct.ImageUrl =

"../Images/" + gwProductList.SelectedDataKey[1];

selectedItem =

this.GetSelectedItem();

}

private Product GetSelectedItem()

{

GridViewRow selectRow = gwProductList.SelectedRow;

Product newItem = new Product();

newItem.ProductID = gwProductList.SelectedValue.ToString();

newItem.ProductName = selectRow.Cells[1].Text;

newItem.ProductType = selectRow.Cells[2].Text;

newItem.ProductColor = selectRow.Cells[3].Text;

newItem.ProductSize = selectRow.Cells[4].Text;

newItem.ProductPrice =

Convert.ToDecimal(selectRow.Cells[5].Text);

return newItem;

}

protected void btnAdd_Click(object sender, EventArgs e)

{

OrderItemList order = OrderItemList.GetOrder();

OrderItem orderItem = order[selectedItem.ProductID];

if (orderItem == null)

{

order.AddItem(selectedItem,

Convert.ToInt32(txtQuantity.Text));

}

else

{

orderItem.AddQuantity(

Convert.ToInt32(txtQuantity.Text));

}

Response.Redirect(

"Cart.aspx");

}

}

OrderItemList.cs

using

System;

using

System.Collections.Generic;

using

System.Web;

using

System.Linq;

///

<summary>

///

Summary description for OrderItemList

///

</summary>

public

class OrderItemList

{

private List<OrderItem> orderItems;

public OrderItemList()

{

orderItems =

new List<OrderItem>();

}

public int Count

{

get { return orderItems.Count; }

}

public OrderItem this[int index]

{

get { return orderItems[index]; }

set { orderItems[index] = value; }

}

public OrderItem this[string id]

{

get

{

foreach (OrderItem c in orderItems)

if (c.Product.ProductID == id) return c;

return null;

}

}

public static OrderItemList GetOrder()

{

OrderItemList order = (OrderItemList)HttpContext.Current.Session["Cart"];

if (order == null)

HttpContext.Current.Session["Cart"] = new OrderItemList();

return (OrderItemList)HttpContext.Current.Session["Cart"];

}

public void AddItem(Product product, int quantity)

{

OrderItem c = new OrderItem(product, quantity);

orderItems.Add(c);

}

}

OrderItem.cs

///

<summary>

///

Summary description for OrderItem

///

</summary>

public

class OrderItem

{

public

OrderItem(){}

public

OrderItem(Product product, int quantity)

{

this.Product = product;

this.Quantity = quantity;

}

public

Product Product { get; set; }

public

int Quantity { get; set; }

public

void AddQuantity(int quantity)

{

this.Quantity += quantity;

}

public

string Display()

{

string displayString = Product.ProductName + " (" + Quantity.ToString()

+

" at " + Product.ProductPrice.ToString("c") + " each)";

return displayString;

}

}