ASPxClientTreeList.StartDragNode Event

Occurs before a node is dragged by an end-user.

Declaration

StartDragNode: ASPxClientEvent<ASPxClientTreeListStartDragNodeEventHandler<ASPxClientTreeList>>

Event Data

The StartDragNode event's data class is ASPxClientTreeListStartDragNodeEventArgs. The following properties provide information specific to this event:

Property	Description
cancel	Gets or sets a value indicating whether the action which raised the event should be canceled. Inherited from ASPxClientTreeListNodeEventArgs.
htmlEvent	Provides access to the parameters associated with the ASPxClientTreeList.NodeClick and ASPxClientTreeList.NodeDblClick events. Inherited from ASPxClientTreeListNodeEventArgs.
nodeKey	Gets the processed node’s key value. Inherited from ASPxClientTreeListNodeEventArgs.
targets	Gets an array of targets where a node can be dragged.

Remarks

The StartDragNode event is raised after an end-user has clicked a node, and allows you to:

• cancel the operation by setting the ASPxClientTreeListNodeEventArgs.cancel property to true.
• specify target elements to which a node can be dragged. The collection of targets can be obtained via the ASPxClientTreeListStartDragNodeEventArgs.targets property.

End-users are allowed to move nodes if the TreeListSettingsEditing.AllowNodeDragDrop option is enabled.

To learn more, see Drag and Drop.

Example

This example demonstrates how to implement node dragging outside the ASPxTreeList. The ASPxClientTreeList.StartDragNode client event is handled to add the cart image to the list of target elements, so that an end-user can drag nodes to the cart. If a node has been dropped to the cart, the cart image changes (in the ASPxClientTreeList.EndDragNode client event handler) and the node is painted red (using the server ASPxTreeList.HtmlRowPrepared event).

The image below shows the result:

ASPX

<dx:ASPxImage id="ASPxImage1" runat="server" ImageUrl="~/Images/cart-empty.png" ClientInstanceName="imageCart" >
</dx:ASPxImage>

<dx:ASPxTreeList ID="ASPxTreeList1" runat="server" AutoGenerateColumns="False" ClientInstanceName="treeList"
    DataSourceID="AccessDataSource1" KeyFieldName="ProductID" ParentFieldName="ParentID" 
    OnCustomCallback="ASPxTreeList1_CustomCallback" OnHtmlRowPrepared="ASPxTreeList1_HtmlRowPrepared">
    <Columns>
        <dx:TreeListTextColumn FieldName="ProductName" VisibleIndex="1">
        </dx:TreeListTextColumn>
        <dx:TreeListTextColumn FieldName="UnitPrice" VisibleIndex="2">
            <PropertiesTextEdit DisplayFormatString="c2">
            </PropertiesTextEdit>
        </dx:TreeListTextColumn>
    </Columns>
        <SettingsEditing AllowNodeDragDrop="True" />
    <ClientSideEvents 
        EndDragNode="function(s, e) {
            if(e.targetElement == imageCart.GetMainElement()) {
                imageCart.SetImageUrl('Images/cart-filled.png');
                e.cancel = true;
                s.PerformCustomCallback(e.nodeKey);
            }
        }" 
        StartDragNode="function(s, e) {
            if(s.GetNodeState(e.nodeKey) == 'Child')
                e.targets.push(imageCart.GetMainElement());
        }" />
</dx:ASPxTreeList>

C#

using System.Collections;
using DevExpress.Web.ASPxEditors;
using DevExpress.Web.ASPxTreeList;

protected void Page_Load(object sender, EventArgs e){
    if (!IsPostBack && !IsCallback)
        Session["ItemsInCart"] = new ArrayList();
}

protected void ASPxTreeList1_CustomCallback(object sender, DevExpress.Web.ASPxTreeList.TreeListCustomCallbackEventArgs e){
    (Session["ItemsInCart"] as ArrayList).Add(e.Argument);
}

protected void ASPxTreeList1_HtmlRowPrepared(object sender, DevExpress.Web.ASPxTreeList.TreeListHtmlRowEventArgs e){
    ArrayList orders = Session["ItemsInCart"] as ArrayList;
    if (orders.Count == 0) return;
    if (orders.Contains(e.NodeKey))
        e.Row.ForeColor = System.Drawing.Color.OrangeRed;
}

VB.NET

Imports System.Collections
Imports DevExpress.Web.ASPxEditors
Imports DevExpress.Web.ASPxTreeList

Protected Sub Page_Load(sender As Object, e As EventArgs)
    If Not IsPostBack AndAlso Not IsCallback Then
        Session("ItemsInCart") = New ArrayList()
    End If
End Sub

Protected Sub ASPxTreeList1_CustomCallback(sender As Object, e As DevExpress.Web.ASPxTreeList.TreeListCustomCallbackEventArgs)
    TryCast(Session("ItemsInCart"), ArrayList).Add(e.Argument)
End Sub

Protected Sub ASPxTreeList1_HtmlRowPrepared(sender As Object, e As DevExpress.Web.ASPxTreeList.TreeListHtmlRowEventArgs)
    Dim orders As ArrayList = TryCast(Session("ItemsInCart"), ArrayList)
    If orders.Count = 0 Then
        Return
    End If
    If orders.Contains(e.NodeKey) Then
        e.Row.ForeColor = System.Drawing.Color.OrangeRed
    End If
End Sub