Question

Preamble

I’m asking this question because even though I’ve read through a lot of ListView resources, I’m still not ‘getting’ it.

Background

I have a bunch of Foo‘s that have a list of items associated with them (known as Bar), and I’m pulling them from the Data Access/Business Logic layer as Dictionary that holds a Foo and its associated Bars. I’d like to spit these items out in on the Webpage into a ListView that holds the Foo.Name on the left, and the List<Bar> on the right in a dropdownlist. (Shown with my beautiful ASCII art below):

ListView

 ------------------------------------------------------------------ |           Name Of Item          |  DropDownList (of List<T>)   | |---------------------------------|  _____________________       | |                foo1             |  |     bar1      | v |       | |                                 |  |_______________|___|       |   ------------------------------------------------------------------ |                                 |  DropDownList (of List<T>)   | |                                 |  _____________________       | |                foo2             |  |     bar2      | v |       | |                                 |  |_______________|___|       | ------------------------------------------------------------------ 

Alright, here’s what’s going on. This is a ListView; The items are pulled from a database into a Dictionary<Foo, List<Bar>>. I’m trying to get the Key Value from the dictionary to show up under ‘Name of Item’, and am trying to get the `List<T> Bar’ to show up as a DropDownList on the right side of the ListView.

Class Diagrams

 -----------------          ----------------- |   Foo         |          |  Bar          | -----------------          ----------------- |  Id           |          |  ItemName     | |  Name         |          |  ItemValue    | |  BarID        |          |               | -----------------          ----------------- 

So to recap, I want to place the Dictionary.Key ‘Name’ into the left side of the ListView, and the Dictionary.Value (which happens to be a list) into a DropdownList on the right side.

So that, for every Key/Value pair, there’d be a Name and a dropdown list that would house each Key’s Value.

But I’m running into problems (obviously), and am hoping someone can tell me what I’m doing wrong.

Code Behind:

  protected Dictionary<Foo, List<Bar>> FooDictionary         {             get;              set;          }  protected void DataBindFooList(List<int> SelectedFoos)         {             System.Web.UI.WebControls.ListView lv = lvFooList;  try             {                 Dictionary<Foo, List<Bar>> fooDictionary =                     new Dictionary<Foo, List<Bar>>();                  foreach (int Foo in SelectedFoos)                 {                  // Build List of Foos to add as Dictionary.Keys                  fooDictionary.Add(fooScalar, Bar)                                      }                 FooDictionary = fooDictionary;                 lv.DataSource = FooDictionary;                 lv.DataBind();                 ddlListOfBars.DataSource = FooDictionary;                 ddlListOfBars.DataValueField = 'ItemValue';                 ddlListOfBars.DataTextField = 'ItemName';                 ddlListOfBars.DataBind();             }             catch (Exception ex)             {                 SetMessage(divFooMsg, 'Unable to retrieve Foos: ' +                  ex.Message, true, true);             } 

The ListView Code:

<asp:ListView ID='lvFooList' runat='server'>    <LayoutTemplate>       <asp:PlaceHolder runat='server' ID='itemPlaceholder'></asp:PlaceHolder>    </LayoutTemplate>       <ItemSeparatorTemplate>          <hr />       </ItemSeparatorTemplate>    <ItemTemplate>       <%#Eval('Name') %>       <asp:DropDownList ID='ddlListOfBars' runat='server'></asp:DropDownList>     </ItemTemplate>    </asp:ListView> 

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The Question(s):

1. Is it possible to use a Dictionary in this way?
2. Any pointers on where I’m going wrong? (Resources, hints, etc. would help)
3. Is there a better way to do this?
4. If this question is clear as mud, please comment so I can figure out how to improve it.

Answer 1

Your problem arises because it doesn’t make sense to databind ddlListOfBars in DataBindFooList(), because there isn’t just one DropDownList to databind. When you call lv.DataBind(), the ListView creates a copy of your ItemTemplate for each Foo, each containing a ddlListOfBars. You need to tell it to bind each DropDownList to the right List<Bar> as it goes. You can do this by setting the datasource of ddlListOfBars with data binding expressions rather than in the code behind:

<ItemTemplate>   <%#Eval('Key.Name') %>   <asp:DropDownList         ID='ddlListOfBars'         runat='server'         DataSource='<%#Eval('Value')%>'         DataValueField='ItemValue'         DataTextField='ItemName' /> </ItemTemplate> 

Note that you also need to use ‘Key.Name’ to get to the name property of your Foo. The individual dictionary items that you’re binding to are KeyValuePair<Foo,List<Bar>>, which has a Key property and a Value property to access the Foo and List<Bar> respectively.

Edit
If you’ve got a lot going on in your ItemTemplate then it can be useful to move the contents out into a user control. The user control can have a strongly-typed property to access the DataItem, and has strongly-typed access to its child controls. This gets you the flexibility of the ItemDataBound event without all the the casting and FindControl() noise. I doubt I’d bother in this case, but it would go something like

<asp:ListView ID='lvFooList' runat='server'> <LayoutTemplate>   <asp:PlaceHolder runat='server' ID='itemPlaceholder'></asp:PlaceHolder> </LayoutTemplate>   <ItemSeparatorTemplate>      <hr />   </ItemSeparatorTemplate> <ItemTemplate>   <uc:ListViewContents DataItem='<%# Container.DataItem %>' /> </ItemTemplate> 

ListViewContents.ascx…

<asp:Label ID='lbName' runat='server'/> <asp:DropDownList ID='ddlListOfBars' runat='server'></asp:DropDownList> 

ListViewContents.ascx.cs…

public KeyValuePair<Foo,List<Bar>> DataItem {     get; set; }  protected override void OnDataBinding(EventArgs e) {     base.OnDataBinding(e);      lbName.Text = DataItem.Key.Name;      ddlListOfBars.DataTextField = 'ItemName';     ddlListOfBars.DataValueField = 'ItemValue';     ddlListOfBars.DataSource = DataItem.Value;     ddlListOfBars.DataBind();    }