ASP.NET Data Binding

1. ASP.NET Data Binding

2. Lecture Overview • Understanding the ASP.NET data binding model

3. What is Data Binding? • We are, while the page executes, getting data into a page or control dynamically through an HTML page

4. Creating a Binding • In the ASPX page (not the C# file), we embed expressions in some “special” expressions

5. Executing a Binding • Data binding has a place in the page lifecycle • It occurs automatically in some cases depending on the setting of control properties • In some cases you must force the binding to execute • Call DataBind() on the page or control • this.DataBind()

6. Binding Example 2 • Bind to a form variable

7. Binding Example 3 • Use data binding to call a function on the current page (The function is named SampleFunction)See DataBindingExpressions1.aspx • <asp:Label ID="Label2" runat="server" • Text="<%# SampleFunction() %>"></asp:Label>

8. Possible Data Sources • Anything that can be enumerated (foreach loop) can serve as a data source • Collections for example • Dictionary and so on • ADO.NET DataSet and DataTable • We bind controls to data sources

9. Binding (Simple) • We associate an ASP control to a single value • It can be just about anything • An executable expression • A variable • A data binding expression • This is what we did in the preceding example

10. Binding (Repeated) • Repeated (list) • We bind to a list (hence repeating data) • Repeated data bind is used with “list” controls

11. Types of Complex Bound Controls • Controls can be bound to a data source • Basically, repeating controls are of three types • List controls use a template for each item found in the data source • Iterative controls allow you to create a custom template for each row that is bound • View controls are the richest (DetailsView, FormView, GridView) • More later

12. List Controls • These are our Listbox, DropDownList, CheckBoxList and RadioButtonList • They display a single field of information having multiple rows • The can be associated with a single-field hidden “key”

13. Important Binding List Controls • DataSourceID: Set to an Access, SQL or other DataSource control • It’s a quoted string • DataSource: Set to a bindable source • DataValueField: Set to the data source field that you want the to behave as a key • DataTextField : Set to the data source field that you want the user to see • The DataKeyField contains the primary key

14. Important Binding List Controls (Example)

15. Binding List Controls • There are a host of list controls that all operate similarly • DropDownList, CheckBoxList, ListBox, RadioButtonList, etc.. • You can use the DataSource / DataMember technique or DataSourceID technique mentioned a moment ago

16. ASP.NET Data Source Controls • They add a layer of abstraction to simplify your life • They create the OleDbDataAdapter, DataSet and DataTable for you • They take care of the binding details too

17. ASP.NET Data Source Controls • SqlDataSource • AccessDataSource • ObjectDataSource • XmlDataSource • And more

18. Data Binding (Using a Data Source - 1 ) • The DataSource and DataMember properties together bind a control instance to a data source (or DataSourceID) • The value varies based on the type of control • Bindable data sources are discussed in a moment • These properties can be set • Using the Properties window • Declaratively in .aspx files • Programmatically • Call DataBind to perform the binding

19. Data Binding(Using a DataSource Control) • The DataSourceID property of a grid or other control contains the name of a data source control • Such as AccessDataSource, ObjectDataSource, SqlDataSource

20. Binding List Controls (Example) • Programmatically bind a ListBox lstDemo.DataSourceID = AccessDataSource1"; lstDemo.DataTextField= "fldInvoiceNumber"; lstDemo.DataBind();

21. List Controls (Members) • SelectedIndex contains the 0-based index of the selected list item • -1 if no item is selected • SelectedItem gets the selected item from the list • SelectedValue gets the value of the selected item • Set AutoPostBack to true to fire a postback when the user selects an item • We have discussed these previously

22. Binding Order • Page.Init and Page.Load events fire • Other control events fire • Updates occur for changed controls (Inserting, Inserted, Updating, Updated events fire) • Page.PreRender fires • Data sources are queried and the data displayed

23. Data-Binding Expressions(Introduction) • Data binding expressions bind a control property to data • Three ways to bind • Create a binding expression • Eval is used to create a one-way read-only binding • Bind is used to create a two-way updatable binding • Data binding expressions are evaluated when the DataBind method is called on the page or control

24. Data-Binding Expressions (Syntax) • Data binding expressions are wrapped by <%# ... %> • Data binding expressions contain executable code • You must (often) explicitly call the DataBind method to force the data binding to happen

25. About Eval and Bind • Eval and Bind must be used inside of a “bound container” such as a repeater or something like that!

26. The DataList Control • It’s an iterative control • It supports selection and editing • Its contents can be displayed horizontally or vertically (RepeatDirection)

27. The DataList Control • Its contents are manipulated using templates similar to the Repeater • ItemTemplate • AlternatingItemTemplate • SelectedItemTemplate • EditItemTemplate • HeaderTemplate • FooterTemplate • SeperatorTemplate

28. Iterative Controls (Introduction) • They use templates to display each row differently • That is, you can customize the layout • Different templates exist for headers, footers, rows and alternating rows • The Repeater, DataList, and DataGrid controls are iterative controls • The Repeater has no predefined styles • The DataList and DataGrid do