DataSource parameter for code-behind property

koevoeter — Tue, 03 Feb 2009 10:19:00 GMT

Here's some code for a server control "PropertyParameter" that you can use as a SelectParameter in your xyzDataSource that binds (one-way!) to a property value that is defined in code behind. This is something I need sometimes and isn't available out-of-the-box.

This method uses reflection and requires the property in code-behind to be public. There are two implementations, one for a Page and one for a UserControl. You will need to specify the Target property if you use it inside a UserControl.

This is how you use it in your markup:

<asp:ObjectDataSource ID="StatusObjectDataSource" runat="server"

    TypeName="Components.WorkflowSecurity.WorkflowComponent"

    SelectMethod="GetAvailableStatusesForEntityType">

    <SelectParameters>

        <controls:PropertyParameter Name="entityType"

            PropertyName="EntityType" Target="Page" />

    </SelectParameters>

</asp:ObjectDataSource>

Here is the the code for the server control:

public class PropertyParameter : Parameter

    public enum PropertyTargetEnum

        Page,

        UserControl

    public string PropertyName { get; set; }

    public PropertyTargetEnum Target { get; set; }

    public PropertyParameter()

        Target = PropertyTargetEnum.Page;

    protected override object Evaluate(

        HttpContext context, Control control)

        if (string.IsNullOrEmpty(PropertyName))

            throw new ArgumentNullException("PropertyName");

        Control targetControl = ResolvePropertyTarget(control);

        Type pageType = targetControl.GetType();

        PropertyInfo pi = pageType.GetProperty(PropertyName,

            BindingFlags.Instance |

            BindingFlags.Public |

            BindingFlags.NonPublic);

        if (pi == null)

            throw new InvalidOperationException(

                string.Format("Property '{0}' not found on {1}.",

                PropertyName, Target));

        return pi.GetValue(targetControl, null);

    private Control ResolvePropertyTarget(Control control)

        switch (Target)

            case PropertyTargetEnum.Page:

                return control.Page;

            case PropertyTargetEnum.UserControl:

                return FindParentUserControl(control);

        throw new ArgumentException("Invalid target type.");

    private UserControl FindParentUserControl(Control control)

        Control parent = control.Parent;

        while (parent != null)

            if (parent is UserControl)

                return (UserControl)parent;

            parent = parent.Parent;

        throw new ArgumentException(string.Format(

            "'{0}' is not inside a UserControl.",

            control.ID));

Btw, there are two common workarounds if you don't like this implementation:

Store the value in a HiddenField and use a ControlParameter instead
Add a Parameter control; implement the OnSelecting event of the DataSource to set the value on the InputParameters collection

KoenV : ObjectDataSource

DataSource parameter for code-behind property