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Expand/Collapse Items

The RadTreeList control supports different modes for expanding and collapsing items. There are three available modes - on the server, on the client, or a mix of the first two. The feature is supported with all data binding modes of RadTreeList.

Configuring expand/collapse mode

In order to enable the feature you need to set the ExpandCollapseMode property of RadTreeList. You can use one of the following options:

  • Server - Items are Expanded/Collapsed on the server. This is the default setting.

  • Client - All items are loaded on the client. Expanding and collapsing is done on the client.

  • Combined - Only expanded items are loaded. By default the items are collapsed. Postback is performed only when an item is expanded for the first time. Any subsequent expand/collapse of this item is performed on the client side.

<telerik:RadTreeList RenderMode="Lightweight" runat="server" ID="RadTreeList1"

Server-side API

Name Type Description
ClientExpandedIndexes property Collection containing the TreeListHierarchyIndexes of the items that are expanded on the client-side. The collection is serialized back and forth to the client.
CollapseAllItems() method Collapses all RadTreeList items.
ExpandAllItems() method Expands all RadTreeList items.
ExpandItemToLevel(TreeListDataItem item, int level) method Expands the specified TreeListDataItem to the specified level.
ExpandToLevel(int level) method Expands all RadTreeList items to the specified level.

The ExpandItemToLevel method allows you to expand all child items recursively. For example:

protected void Button1_Click(object sender, EventArgs e)
    foreach (TreeListDataItem item in RadTreeList1.Items)
        //find the item you want to expand
        if (item.GetDataKeyValue("ID").ToString() == "1")
            if (item.CanExpand)
                RadTreeList1.ExpandItemToLevel(item, int.MaxValue);
            //the collection will be modified as items expand, so the loop will throw exceptions if not stopped
Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    For Each item As TreeListDataItem In RadTreeList1.Items
        'find the item you want to expand
        If item.GetDataKeyValue("ID").ToString() = "1" Then
            If item.CanExpand Then
                RadTreeList1.ExpandItemToLevel(item, Integer.MaxValue)
            End If
            'the collection will be modified as items expand, so the loop will throw exceptions if not stopped
            Exit For
        End If
End Sub

Modifying ClientExpandedIndexes can cause unexpected behavior. It is recommended not to modify the collection. Nevertheless, if you need to modify it you should execute caution.

Have in mind that the ClientExpandedIndexes should be used when expand/collapse is performed on the client. If expand/collapse is done server-side you should use the ExpandedIndexes property.

Client-side API

Below is a list of the properties and methods that can be used with the expand/collapse functionality.

Name Type Description
get_clientExpanded property Returns boolean value indicating if an item is expanded.
set_clientExpanded(value) property Sets the expanded state of an item. Note that changing the state of an item will not expand or collapse it.
toggleExpandCollapse method Toggles the state of an item.

Item state persistance

The expanded/collapsed state of the items is persisted after postback by default.

See Also

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