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Accessing Expression Items

Accessing Items

RadFilter exposes the ExpressionItemCreated event which is fired after each item creation.It provides a more easy and intuitive way of accessing the filter expression items. Depending on expressionthat was created the item in the arguments could be either RadFilterSingleExpressionItem or RadFilterGroupExpression.

Below is a sample code implementation which demonstrates how you can manipulate the filter items. The code logic forbids the creation of sub-group expressions by hiding the AddGroupExpressionButton and populates the RadFilterDropDownEditor with data.

<div class="filterDiv">
    <telerik:RadFilter RenderMode="Lightweight" runat="server" ID="RadFilter1" FilterContainerID="RadGrid1" ShowApplyButton="true" 
            <telerik:RadFilterDropDownEditor FieldName="ShipCountry" DataTextField="ShipCountry"
                DataValueField="ShipCountry" />
<telerik:RadGrid RenderMode="Lightweight" runat="server" ID="RadGrid1" AutoGenerateColumns="false" DataSourceID="SqlDataSource1"
    AllowPaging="true" AllowSorting="true" AllowFilteringByColumn="true">
    <MasterTableView IsFilterItemExpanded="false" CommandItemDisplay="Top">
            <telerik:GridNumericColumn DataField="OrderID" HeaderText="OrderID" DataType="System.Int32">
            <telerik:GridDateTimeColumn DataField="OrderDate" HeaderText="OrderDate" DataFormatString="{0:MM/dd/yyyy}">
            <telerik:GridNumericColumn DataField="ShipVia" HeaderText="ShipVia" DataType="System.Int32">
            <telerik:GridBoundColumn DataField="ShipName" HeaderText="ShipName">
            <telerik:GridBoundColumn DataField="ShipAddress" HeaderText="ShipAddress">
            <telerik:GridNumericColumn DataField="Freight" HeaderText="Freight" DataType="System.Decimal">
            <telerik:GridNumericColumn DataField="ShipCountry" HeaderText="ShipCountry">
<asp:SqlDataSource runat="server" ID="SqlDataSource1" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
    SelectCommand="Select OrderID, OrderDate, ShipVia, ShipName, ShipAddress, Freight, ShipCountry FROM Orders">
public DataTable GetDataTable(string query)
    String ConnString = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString;
    SqlConnection conn = new SqlConnection(ConnString);
    SqlDataAdapter adapter = new SqlDataAdapter();
    adapter.SelectCommand = new SqlCommand(query, conn);

    DataTable myDataTable = new DataTable();


    return myDataTable;

protected void RadFilter1_ExpressionItemCreated(object sender, RadFilterExpressionItemCreatedEventArgs e)

    // Populate the RadDropDownList control for every ShipCountry field editor
    RadFilterSingleExpressionItem singleItem = e.Item as RadFilterSingleExpressionItem;
    if (singleItem != null && singleItem.FieldName == "ShipCountry" && singleItem.IsSingleValue)
        RadDropDownList dropDownList = singleItem.InputControl as RadDropDownList;
        dropDownList.DataSource = GetDataTable("SELECT DISTINCT ShipCountry FROM Orders");

    // Removes the AddGroupExpressionButton for group expression other than the root group
    RadFilterGroupExpressionItem groupItem = e.Item as RadFilterGroupExpressionItem;
    if (groupItem != null)
        if (groupItem.IsRootGroup) groupItem.RemoveButton.Visible = false;
        else groupItem.AddGroupExpressionButton.Visible = false;
Public Function GetDataTable(query As String) As DataTable
    Dim ConnString As [String] = ConfigurationManager.ConnectionStrings("NorthwindConnectionString").ConnectionString
    Dim conn As New SqlConnection(ConnString)
    Dim adapter As New SqlDataAdapter()
    adapter.SelectCommand = New SqlCommand(query, conn)

    Dim myDataTable As New DataTable()

    End Try

    Return myDataTable
End Function

Protected Sub RadFilter1_ExpressionItemCreated(sender As Object, e As RadFilterExpressionItemCreatedEventArgs) Handles RadFilter1.ExpressionItemCreated

    ' Populate the RadDropDownList control for every ShipCountry field editor
    Dim singleItem As RadFilterSingleExpressionItem = TryCast(e.Item, RadFilterSingleExpressionItem)
    If singleItem IsNot Nothing AndAlso singleItem.FieldName = "ShipCountry" AndAlso singleItem.IsSingleValue Then
        Dim dropDownList As RadDropDownList = TryCast(singleItem.InputControl, RadDropDownList)
        dropDownList.DataSource = GetDataTable("SELECT DISTINCT ShipCountry FROM Orders")
    End If

    ' Removes the AddGroupExpressionButton for group expression other than the root group
    Dim groupItem As RadFilterGroupExpressionItem = TryCast(e.Item, RadFilterGroupExpressionItem)
    If groupItem IsNot Nothing Then
        If groupItem.IsRootGroup Then
            groupItem.RemoveButton.Visible = False
            groupItem.AddGroupExpressionButton.Visible = False
        End If
    End If
End Sub

In the tables below are listed the properties of the expression items according to the type.


Property Description
FunctionalInterfaceContainer Gets the container holding the links menu - the GroupOperation(for RadFilterGroupExpressionItem), FilterFunction and the editor FieldName.
ToolsInterfaceContainer Gets the container holding item specific controls. An input control for the RadFilterSingleExpressionItem and AddGroupExpression, AddItemExpression for the RadFilterGroupExpressionItem.
RemoveButton Gets a reference to the remove button which removes an expression from the RadFilter expression tree.


Property Description
GroupOperationChooserLink Gets the HyperLink control which chooses the item expression GroupOperation value
AddExpressionButton Gets the LinkButton control which adds a new RadFilterSingleExpressionItem to the RadFilter expression items tree
AddGroupExpressionButton Gets the LinkButton control which adds a new RadFilterGroupExpressionItem to the RadFilter expression items tree


Property Description
FieldName Gets the associated RadFilterNonGroupExpression.FieldName value
IsSingleValue Gets a value indicating if the expression item have only one value. If the property returns true the InputControl value will not be null
IsDoubleValue Gets a value indicating if the expression item have two values (between filtering is performed). If the property returns true the SecondInputControl value will not be null
InputControl The input control which determines an expression value. The property could return null if the Expression is not of type IRadFilterValueExpression
SecondInputControl The second input control which determines the second expression value when performing between filtering. The property will not return null only when performing between filtering
FieldNameChooserLink Gets the HyperLink control which is used for choosing the FieldName
FilterFunctionChooserLink Gets the HyperLink control which is used for choosing the FilterFunction
BetweenDelimeter Gets the LiteralControl which is placed between the two input controls when the filter function is "Between" or "NotBetween"
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