DropDownTree HtmlHelper Overview
The Telerik UI DropDownTree HtmlHelper for ASP.NET Core is a server-side wrapper for the Kendo UI DropDownTree widget.
The DropDownTree represents an editor of hierarchical data, rendered in a tree-like structure, which provides multiple selection option and custom nodes.
Initializing the DropDownTree
The following example demonstrates how to define the DropDownTree by using the DropDownTree HtmlHelper.
@(Html.Kendo().DropDownTree()
.Name("dropdowntree")
.DataTextField("Name")
.DataValueField("id")
.DataSource(dataSource => dataSource
.Read(read => read
.Action("Read_DropDownTreeData", "Home")
)
)
)
public static IList<HierarchicalViewModel> GetHierarchicalData()
{
var result = new List<HierarchicalViewModel>()
{
new HierarchicalViewModel() { ID = 1, ParentID = null, HasChildren = true, Name = "Parent item" },
new HierarchicalViewModel() { ID = 2, ParentID = 1, HasChildren = true, Name = "Parent item" },
new HierarchicalViewModel() { ID = 3, ParentID = 1, HasChildren = false, Name = "Item" },
new HierarchicalViewModel() { ID = 4, ParentID = 2, HasChildren = false, Name = "Item" },
new HierarchicalViewModel() { ID = 5, ParentID = 2, HasChildren = false, Name = "Item" }
};
return result;
}
public IActionResult Read_DropDownTreeData(int? id)
{
var result = GetHierarchicalData()
.Where(x => id.HasValue ? x.ParentID == id : x.ParentID == null)
.Select(item => new {
id = item.ID,
Name = item.Name,
hasChildren = item.HasChildren
});
return Json(result);
}
Basic Configuration
The following example demonstrates the basic configuration of the DropDownTree HtmlHelper.
@(Html.Kendo().DropDownTree()
.Name("dropdowntree")
.Checkboxes(true)
.Filter(FilterType.Contains)
.DataTextField("Name")
.DataTextField("ID")
.DataSource(dataSource => dataSource
.Read(read => read
.Action("Employees", "Home")
)
)
)
Functionality and Features
Events
The following example demonstrates the available DropDownTree events and how an event handler could be implemented for each of them.
For an example on basic DropDownTree events, refer to the demo on using the events of the DropDownTree.
@(Html.Kendo().DropDownTree()
.Name("dropdowntree")
.DataTextField("Name")
.DataSource(dataSource => dataSource
.Read(read => read
.Action("Employees", "Home")
)
)
.Events(events => events
.DataBound("onDataBound")
.Change("onChange")
.Select("onSelect")
.Close("onClose")
.Open("onOpen")
.Filtering("onFiltering")
)
)
<script type="text/javascript">
function onDataBound(e) {
console.log('DropDownTree instance:', e.sender);
}
function onChange(e) {
console.log('Selected node changed to:', e.sender.select());
}
function onSelect(e) {
console.log('Selected node:', e.node);
}
function onClose(e) {
console.log('DropDownTree instance:', e.sender);
}
function onOpen(e) {
console.log('DropDownTree instance:', e.sender);
}
function onFiltering(e) {
console.log('Folter:', e.filter);
}
</script>
Referencing Existing Instances
To reference an existing DropDownTree instance, use the jQuery.data() configuration option. Once a reference is established, use the DropDownTree client-side API to control its behavior.
// Place the following after your Telerik UI DropDownTree for ASP.NET Core declaration.
<script>
$(document).ready(function() {
// The Name() of the DropDownTree is used to get its client-side instance.
var dropdowntree = $("#dropdowntree").data("kendoDropDownTree");
});
</script>