DataBinder.Eval Method
Definition
Important
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Uses reflection to parse and evaluate a data-binding expression against an object at run time.
Overloads
| Eval(Object, String) |
Evaluates data-binding expressions at run time. |
| Eval(Object, String, String) |
Evaluates data-binding expressions at run time and formats the result as a string. |
Remarks
Starting in .NET Framework 4.5, you can use model binding to simplify some of the tasks that you had to perform through data-binding in earlier versions. For a tutorial series on using model binding with Web Forms, see Model Binding and Web Forms.
Eval(Object, String)
Evaluates data-binding expressions at run time.
public:
static System::Object ^ Eval(System::Object ^ container, System::String ^ expression);public static object Eval (object container, string expression);static member Eval : obj * string -> objPublic Shared Function Eval (container As Object, expression As String) As ObjectParameters
- container
- Object
The object reference against which the expression is evaluated. This must be a valid object identifier in the page's specified language.
- expression
- String
The navigation path from the container object to the public property value to be placed in the bound control property. This must be a string of property or field names separated by periods, such as Tables[0].DefaultView.[0].Price in C# or Tables(0).DefaultView.(0).Price in Visual Basic.
Returns
An Object instance that results from the evaluation of the data-binding expression.
Exceptions
expression is null or is an empty string after trimming.
Examples
The following examples show how to use the Eval method to bind data to Repeater control. It requires a data class named Product.
public class Product
{
public int ProductID { get; set; }
public string Name { get; set; }
public double Price { get; set; }
}
Public Class Product
Public Property ProductID As Integer
Public Property Name As String
Public Property Price As Double
End Class
The code-behind file loads test data and binds that data to a Repeater control.
public partial class ShowProducts : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
var products = new List<Product>();
products.Add(new Product() { ProductID = 1, Name = "Bike", Price = 150.00 });
products.Add(new Product() { ProductID = 2, Name = "Helmet", Price = 19.99 });
products.Add(new Product() { ProductID = 3, Name = "Tire", Price = 10.00 });
ProductList.DataSource = products;
ProductList.DataBind();
}
}
Public Class ShowProducts
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim products As New List(Of Product)()
products.Add(New Product With {.ProductID = 1, .Name = "Bike", .Price = 150.0})
products.Add(New Product With {.ProductID = 2, .Name = "Helmet", .Price = 19.99})
products.Add(New Product With {.ProductID = 3, .Name = "Tire", .Price = 10.0})
ProductList.DataSource = products
ProductList.DataBind()
End Sub
End Class
In the declarative syntax for the Repeater control, you use the Eval method with Container.DataItem for the container parameter.
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# DataBinder.Eval(Container.DataItem, "Name") %> for only <%# DataBinder.Eval(Container.DataItem, "Price", "{0:c}") %>
<br />
<a href='<%# DataBinder.Eval(Container.DataItem, "ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# DataBinder.Eval(Container.DataItem, "Name") %> for only <%# DataBinder.Eval(Container.DataItem, "Price", "{0:c}") %>
<br />
<a href='<%# DataBinder.Eval(Container.DataItem, "ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
Or, you can call Eval function and not include the container parameter.
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# Eval("Name") %> for only <%# Eval("Price", "{0:c}") %>
<br />
<a href='<%# Eval("ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# Eval("Name") %> for only <%# Eval("Price", "{0:c}") %>
<br />
<a href='<%# Eval("ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
Remarks
The value of the expression parameter must evaluate to a public property.
This method is automatically called when you create data bindings in a rapid application development (RAD) designer such as Visual Studio. You can also use it declaratively to simplify casting to a text string. To do so, you use the <%# %> expression syntax, as used in standard ASP.NET data binding.
This method is particularly useful when binding data to controls that are in a templated list.
Note
Because this method performs late-bound evaluation, using reflection at run time, it can cause performance to noticeably slow compared to standard ASP.NET data-binding syntax.
For any of the list Web controls, such as GridView, DetailsView, DataList, or Repeater, container should be Container.DataItem. If you are binding against the page, container should be Page.
Starting in .NET Framework 4.5, you can use model binding to simplify some of the tasks that you had to perform through data-binding in earlier versions. For a tutorial series on using model binding with Web Forms, see Model Binding and Web Forms.
See also
Applies to
Eval(Object, String, String)
Evaluates data-binding expressions at run time and formats the result as a string.
public:
static System::String ^ Eval(System::Object ^ container, System::String ^ expression, System::String ^ format);public static string Eval (object container, string expression, string format);static member Eval : obj * string * string -> stringPublic Shared Function Eval (container As Object, expression As String, format As String) As StringParameters
- container
- Object
The object reference against which the expression is evaluated. This must be a valid object identifier in the page's specified language.
- expression
- String
The navigation path from the container object to the public property value to be placed in the bound control property. This must be a string of property or field names separated by periods, such as Tables[0].DefaultView.[0].Price in C# or Tables(0).DefaultView.(0).Price in Visual Basic.
- format
- String
A .NET Framework format string (like those used by Format(String, Object)) that converts the Object instance returned by the data-binding expression to a String object.
Returns
A String object that results from evaluating the data-binding expression and converting it to a string type.
Examples
The following examples show how to use the Eval method to bind data to Repeater control. It requires a data class named Product.
public class Product
{
public int ProductID { get; set; }
public string Name { get; set; }
public double Price { get; set; }
}
Public Class Product
Public Property ProductID As Integer
Public Property Name As String
Public Property Price As Double
End Class
The code-behind file loads test data and binds that data to a Repeater control.
public partial class ShowProducts : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
var products = new List<Product>();
products.Add(new Product() { ProductID = 1, Name = "Bike", Price = 150.00 });
products.Add(new Product() { ProductID = 2, Name = "Helmet", Price = 19.99 });
products.Add(new Product() { ProductID = 3, Name = "Tire", Price = 10.00 });
ProductList.DataSource = products;
ProductList.DataBind();
}
}
Public Class ShowProducts
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim products As New List(Of Product)()
products.Add(New Product With {.ProductID = 1, .Name = "Bike", .Price = 150.0})
products.Add(New Product With {.ProductID = 2, .Name = "Helmet", .Price = 19.99})
products.Add(New Product With {.ProductID = 3, .Name = "Tire", .Price = 10.0})
ProductList.DataSource = products
ProductList.DataBind()
End Sub
End Class
In the declarative syntax for the Repeater control, you use the Eval method with Container.DataItem for the container parameter.
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# DataBinder.Eval(Container.DataItem, "Name") %> for only <%# DataBinder.Eval(Container.DataItem, "Price", "{0:c}") %>
<br />
<a href='<%# DataBinder.Eval(Container.DataItem, "ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# DataBinder.Eval(Container.DataItem, "Name") %> for only <%# DataBinder.Eval(Container.DataItem, "Price", "{0:c}") %>
<br />
<a href='<%# DataBinder.Eval(Container.DataItem, "ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
Or, you can call Eval function and not include the container parameter.
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# Eval("Name") %> for only <%# Eval("Price", "{0:c}") %>
<br />
<a href='<%# Eval("ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
<asp:Repeater ID="ProductList" runat="server">
<ItemTemplate>
<%# Eval("Name") %> for only <%# Eval("Price", "{0:c}") %>
<br />
<a href='<%# Eval("ProductID", "details.asp?id={0}") %>'>See Details</a>
<br />
<br />
</ItemTemplate>
</asp:Repeater>
Remarks
The value of expression must evaluate to a public property.
For more information about format strings in the .NET Framework, see Formatting Types.
This method is automatically called when you create data bindings in a rapid application development (RAD) designer such as Visual Studio. You can also use it declaratively to convert the Object resulting from the data-binding expression to a String. To use the method declaratively, use the <%# %> expression syntax, as used in standard ASP.NET data binding.
This method is particularly useful when binding data to controls that are in a templated list.
Note
Because this method performs late-bound evaluation, using reflection at run time, it can cause performance to noticeably slow compared to standard ASP.NET data-binding syntax. Use this method judiciously, particularly when string formatting is not required.
For any of the list Web controls, such as GridView, DetailsView, DataList, or Repeater, container should be Container.DataItem. If you are binding against the page, container should be Page.
Starting in .NET Framework 4.5, you can use model binding to simplify some of the tasks that you had to perform through data-binding in earlier versions. For a tutorial series on using model binding with Web Forms, see Model Binding and Web Forms.
