Practical ASP.NET
Extending the ListView
Peter moves beyond the basics of setting up a ListView to add databound controls, control headers and footers and turn on updating.
In my previous column (
Working with the ListView) I made the claim that the ListView was the most powerful control because, like a GridView, it allowed you to display multiple rows but, like a FormView, allowed you complete freedom in the format for each row. In that column I looked at setting up the ListView by leveraging the options on the ListView's SmartTag.
In this column I'm going to go beyond those basics.
For instance, you may want to add a databound control, like a DropDownList, to your templates. The first step is to add a DataSource to fill your DropDownList. Fortunately, you can add the DataSource to the page outside of the ListView where you can work with it in a visual designer.
Once you've added the DataSource, you can drag the DropDownList onto a template in the ListView. After the DropDownList is added, you'll need to set at least three properties on the DropDownList: the Text property (to have the correct item in the list highlighted) and the properties for DataSourceId and DataTextField (to have the list filled from the DataSource). You'll have to set all the properties without the benefit of IntelliSense (and, with the Text property, you'll need to use the Bind function) so careful typing is required.
The result would look like this:
<asp:DropDownList ID="CompanyNameCheckBoxList" runat="server"
Text='<%# Bind("CompanyName") %>'
DataSourceID="ObjectDataSource2"
DataTextField="CompanyName" />
In addition to the templates for displaying data, your ListView also includes a LayoutTemplate that allows you to specify a header and footer for your ListView. The LayoutTemplate must include a control with its id set to itemPlaceHolder (uppercase letters are optional). Each of the other templates are inserted into this control, which is repeated once for each row retrieved.
The simplest possible LayoutTemplate looks like this:
<LayoutTemplate>
<span id="itemPlaceholder" runat="server"></span>
</LayoutTemplate>
The LayoutTemplate allows you to place a header and footer around your templates. Your ListView may not require any headings. If, for instance, you're using each template as a mini-form, then column headings won't make sense. But, if you're using a column-based format, you will want to have headings. And, regardless of the format of your rows, if you're allowing the user to page through data, then you'll want a footer with a Pager control. If you're supporting paging, your simplest LayoutTemplate looks like this:
<LayoutTemplate>
<span ID="itemPlaceholder" runat="server"/>
<asp:DataPager ID="DataPager1" runat="server">
<Fields>
<asp:NextPreviousPagerField ButtonType="Button"
ShowFirstPageButton="True"
ShowLastPageButton="True" />
</Fields>
</asp:DataPager>
</LayoutTemplate>
At this point, you're probably ready to start thinking about updates, inserts and deletes. The most important point is that you should either enable updating before you make any changes to the templates or be prepared to do some typing in Source View. Of course, if you're working with the ListView, you've already resigned yourself to typing in the Source View.
The reason that you don't want to enable editing after you made changes to the templates is that enabling editing (or deleting or inserting) is that all of the templates are regenerated, wiping out any customizations you've made. However, you can turn on editing by inserting an edit button into the ItemTemplate. The key item is that the button's CommandName must be set to "Edit" (with or without the uppercase "E"), as in this example:
<ItemTemplate>
<tr style="background-color:#DCDCDC;color: #000000;">
<td>
<asp:Button ID="MyButton" runat="server" CommandName="Edit"
Text="Change" />
</td>
... rest of ItemTemplate...
If this all seems like a lot more work than using the GridView, the good news is that the event model for the ListView is virtually identical to the GridView with ItemUpdating/ItemUpdated and other events. So, once you've got the ListView set up, you can return to the coding that you're used to.
About the Author
Peter Vogel is a system architect and principal in PH&V Information Services. PH&V provides full-stack consulting from UX design through object modeling to database design. Peter tweets about his VSM columns with the hashtag #vogelarticles. His blog posts on user experience design can be found at http://blog.learningtree.com/tag/ui/.