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When working with templated controls such as the
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You can also create templates as user controls and bind them dynamically to controls on your page. For details, see How to: Create Templated ASP.NET User Controls. |
You can create templates in code for all controls that use templates: the DataList,
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There are a few differences when creating template columns for the GridView control. For details, see Creating a Custom Column in a GridView Web Server Control. |
Creating the Template Class
To create dynamic templates, you create a template class that you can then instantiate when needed.
To create a template class
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Create a new class that implements the
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Optionally, pass into the class's constructor a value that the class can use to determine what type of template to create (ItemTemplate, AlternatingItemTemplate, and so on).
Note A type-safe way to pass the template type to the constructor is to add a parameter to the constructor with the type
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In the class, implement the
This method provides a way to insert an instance of text and controls into the specified container.
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In the InstantiateIn method, create the controls for the template item, set their properties, and then add them to the parent's Controls collection.
You can access the parent control via the reference passed to the InstantiateIn method.
Note You cannot directly add static text to the Controls collection, but you can create controls like the
The following code example illustrates a complete template class that displays some static text ("Item number:") and a counter. The counter is maintained as a static value (shared in Visual Basic) named
itemcountand incremented each time a new item is created. The class defines an explicit constructor that accepts a ListItemType enumeration value to indicate what type of template is being created. Depending on what type of template is being created, the code creates different types of controls and adds them to the Controls collection of the parent control. The end result is an HTML table with a different background color for the alternating item template.Visual BasicВ 
Copy CodePublic Class MyTemplate Implements ITemplate Shared itemcount As Integer = 0 Dim TemplateType As ListItemType Sub New(ByVal type As ListItemType) TemplateType = type End Sub Sub InstantiateIn(ByVal container As Control) _ Implements ITemplate.InstantiateIn Dim lc As New Literal() Select Case TemplateType Case ListItemType.Header lc.Text = "<TABLE border=1><TR><TH>Items</TH></TR>" Case ListItemType.Item lc.Text = "<TR><TD>Item number: " & itemcount.ToString _ & "</TD></TR>" Case ListItemType.AlternatingItem lc.Text = "<TR><TD bgcolor=lightblue>Item number: " _ & itemcount.ToString & "</TD></TR>" Case ListItemType.Footer lc.Text = "</TABLE>" End Select container.Controls.Add(lc) itemcount += 1 End Sub End ClassC#В Copy Codepublic class MyTemplate : ITemplate { static int itemcount = 0; ListItemType templateType; public MyTemplate(ListItemType type) { templateType = type; } public void InstantiateIn(System.Web.UI.Control container) { Literal lc = new Literal(); switch (templateType) { case ListItemType.Header: lc.Text = "<TABLE border=1><TR><TH>Items</TH></TR>"; break; case ListItemType.Item: lc.Text = "<TR><TD>Item number: " + itemcount.ToString() + "</TD></TR>"; break; case ListItemType.AlternatingItem: lc.Text = "<TR><TD bgcolor=lightblue>Item number: " + itemcount.ToString() + "</TD></TR>"; break; case ListItemType.Footer: lc.Text = "</TABLE>"; break; } container.Controls.Add(lc); itemcount += 1; } }
Using the Dynamic Template
When you have a dynamic template available, you can instantiate it in code.
To use a dynamic template
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Create an instance of your dynamic template, passing it an item type value if appropriate.
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Assign the instance to one of the template properties of the templated control, such as the ItemTemplate, AlternatingItemTemplate, HeaderTemplate properties.
The following code example shows how to use the dynamic template with a Repeater control. In this example, the templates are instantiated while the page is being loaded and before the control is bound to its data source.
Visual BasicВ Copy CodePrivate Sub Page_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load Dim conn As SqlConnection = _ New SqlConnection(ConfigurationManager.ConnectionStrings("Northwind").ConnectionString) Dim SqlDataAdapter1 As SqlDataAdapter Dim DsCategories1 As DataSet SqlDataAdapter1 = New SqlDataAdapter("SELECT CategoryID, CategoryName FROM Categories", conn) DsCategories1 = new Dataset() Repeater1.HeaderTemplate = New MyTemplate(ListItemType.Header) Repeater1.ItemTemplate = New MyTemplate(ListItemType.Item) Repeater1.AlternatingItemTemplate = _ New MyTemplate(ListItemType.AlternatingItem) Repeater1.FooterTemplate = New MyTemplate(ListItemType.Footer) SqlDataAdapter1.Fill(DsCategories1, "Categories") Repeater1.DataSource = DsCategories1.Tables("Categories") Repeater1.DataBind() End SubC#В Copy Codeprivate void Page_Load(object sender, System.EventArgs e) { SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["Northwind"].ConnectionString); SqlDataAdapter sqlDataAdapter1; DataSet dsCategories1; sqlDataAdapter1 = new SqlDataAdapter("SELECT CategoryID, CategoryName FROM Categories", conn); dsCategories1 = new DataSet(); Repeater1.HeaderTemplate = new MyTemplate(ListItemType.Header); Repeater1.ItemTemplate = new MyTemplate(ListItemType.Item); Repeater1.AlternatingItemTemplate = new MyTemplate(ListItemType.AlternatingItem); Repeater1.FooterTemplate = new MyTemplate(ListItemType.Footer); sqlDataAdapter1.Fill(dsCategories1, "Categories"); Repeater1.DataSource = dsCategories1.Tables["Categories"]; Repeater1.DataBind(); }
Adding Data Binding to Templates
You can access data in a template class in various ways, depending on how you have created the class. One way is the way the page framework itself implements data binding—when you add controls to the template, you also add a handler for their
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You cannot embed a data-binding expression as a string when creating controls in the template, as you do when defining templates at design time, because data-binding expressions are converted into code before your template is created. |
In the handler for the DataBinding event, you have an opportunity to manipulate the contents of the control. Typically (but not necessarily), you fetch data from somewhere and assign it to the control's Text property.
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For background on data binding in ASP.NET Web pages, see Accessing Data with ASP.NET. |
To add data binding to a dynamic template, you must do the following:
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Add a data-binding event handler to the controls you create in the template.
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Create the handler that you are binding to. In the handler, get the data that you want to bind to and assign it to the appropriate property of the control being bound.
To add the data-binding event handler
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After creating a control in the dynamic template, add a reference to an event handler for the control's DataBinding event. (You will create the event handler in the next procedure).
The following code example shows a portion of a template class illustrating how you can bind a newly created control to a method named
TemplateControl_DataBinding:Visual BasicВ Copy CodeDim lc As New Literal() Select Case TemplateType Case ListItemType.Item lc.Text = "<TR><TD>" AddHandler lc.DataBinding, AddressOf TemplateControl_DataBinding End SelectC#В Copy Codecase ListItemType.Item: lc.Text = "<TR><TD>"; lc.DataBinding += new EventHandler(TemplateControl_DataBinding); break;
In the preceding example, the text you add to the literal control's Text property is different than in the previous example. It contains only the beginning of the table row and cell for the item template. You will complete the cell and row in the data-binding event handler.
The next step is to create the event handler that will be called when the control is data bound.
To create the handler for the DataBinding event
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Create a method that is part of your template class and is a peer of the class's other methods (such as InstantiateIn). The handler's name must match the name you used when binding the event earlier. The method should have the following signature:
Visual BasicВ Copy CodePrivate Sub TemplateControl_DataBinding(ByVal sender As Object, _ ByVal e As System.EventArgs)
C#В Copy Codeprivate void TemplateControl_DataBinding(object sender, System.EventArgs e)
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Get a reference to the DataItem object containing the data by doing the following:
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Get a reference to the template item. You create a variable to hold the reference and then assign it the value you get from your control's
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Use that reference to get the naming container's (the template item's)
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Extract the individual data element (data column, for example) from the DataItem object and use it to set a property of the control you are binding.
The following code example illustrates one way to perform data binding within a dynamic template. It shows a complete data-binding event handler for Literal controls being created in a template for a Repeater control.
Visual BasicВ Copy CodePrivate Sub TemplateControl_DataBinding(ByVal sender As Object, _ ByVal e As System.EventArgs) Dim lc As Literal lc = CType(sender, Literal) Dim container As RepeaterItem container = CType(lc.NamingContainer, RepeaterItem) lc.Text &= DataBinder.Eval(container.DataItem, "CategoryName") lc.Text &= "</TD></TR>" End SubC#В Copy Codeprivate void TemplateControl_DataBinding(object sender, System.EventArgs e) { Literal lc; lc = (Literal)sender; RepeaterItem container = (RepeaterItem)lc.NamingContainer; lc.Text += DataBinder.Eval(container.DataItem, "CategoryName"); lc.Text += "</TD></TR>"; }Note If you have multiple types of controls in your templates, you need to create a different data-binding event handler for each control type.
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See Also
