DxTreeList.AllowedDropTarget Property

Specifies allowed drag-and-drop targets.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.Grid.v26.1.dll

NuGet Package: DevExpress.Blazor

Declaration

[DefaultValue(TreeListAllowedDropTarget.Internal)]
[Parameter]
public TreeListAllowedDropTarget AllowedDropTarget { get; set; }

Property Value

Type	Default	Description
TreeListAllowedDropTarget	Internal	An enumeration value.

Available values:

Name	Description
None	Users cannot reorder rows or drop them onto this TreeList from another component.
Internal	Users can reorder rows within this TreeList.
External	Users can drop rows onto other components.
All	Users can reorder rows within this TreeList and drop them onto other components.

Remarks

Activate the AllowDragRows option to render drag handles for data rows. The AllowedDropTarget property specifies whether these handles allow users to reorder rows or move them to other components. In all modes, except for None, the TreeList component allows users to change its hierarchy. Handle the target component’s ItemsDropped event to update the data source.

In the following example, the Grid allows users to drag rows to external targets. The TreeList accepts rows from the Grid and allows row reordering:

Run Demo: Drag and Drop Rows - Between Components

@inject IEmployeeTaskDataProvider EmployeeTaskDataProvider
<div class="components-container">
    <DxTreeList @ref="PlannedTasksTreeList"
                Data="PlannedTasks"
                KeyFieldName="Id"
                ParentKeyFieldName="ParentId"
                AllowSort="false"
                AutoExpandAllNodes="true"
                AllowDragRows="true"
                AllowedDropTarget="TreeListAllowedDropTarget.All"
                VirtualScrollingEnabled="true"
                SizeMode="Params.SizeMode"
                ItemsDropped="TreeList_ItemsDropped">
        <Columns>
            <DxTreeListDataColumn @ref="TreeList_NameDataColumn" FieldName="Name" Caption="Task" />
            <DxTreeListDataColumn FieldName="Priority" Width="100px" CaptionAlignment="TreeListTextAlignment.Center" TextAlignment="TreeListTextAlignment.Center">
                <CellDisplayTemplate>
                    @DemoTemplateIconUtils.GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItem)
                </CellDisplayTemplate>
            </DxTreeListDataColumn>
        </Columns>
        <DragHintTextTemplate>
            @if(context.DataItems[0] != null) {
                <span class="dxbl-text">@context.GetDisplayText(TreeList_NameDataColumn)</span>
                <span class="dxbl-text">@DemoTemplateIconUtils.GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItems[0])</span>
            }
        </DragHintTextTemplate>
        <ToolbarTemplate>
            <DxToolbar Title="Planned Tasks" />
        </ToolbarTemplate>
    </DxTreeList>

    <DxGrid Data="PendingTasks"
            AllowSelectRowByClick="true"
            SelectionMode="GridSelectionMode.Multiple"
            TextWrapEnabled="false"
            AllowDragRows="true"
            AllowedDropTarget="GridAllowedDropTarget.All"
            VirtualScrollingEnabled="true"
            SizeMode="Params.SizeMode"
            ItemsDropped="Grid_ItemsDropped">
        <Columns>
            <DxGridSelectionColumn Width="40px" />
            <DxGridDataColumn @ref="Grid_NameDataColumn" FieldName="Name" Caption="Task" />
            <DxGridDataColumn FieldName="Priority" Width="100px" CaptionAlignment="GridTextAlignment.Center" TextAlignment="GridTextAlignment.Center">
                <CellDisplayTemplate>
                    @DemoTemplateIconUtils.GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItem)
                </CellDisplayTemplate>
            </DxGridDataColumn>
        </Columns>
        <DragHintTextTemplate>
            @if(context.DataItems.Count == 1) {
                <span class="dxbl-text">@context.GetDisplayText(Grid_NameDataColumn)</span>
                <span class="dxbl-text">@DemoTemplateIconUtils.GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItems[0])</span>
            }
            else {
                <span class="dxbl-text">@(context.DataItems.Count) tasks</span>
            }
        </DragHintTextTemplate>
        <ToolbarTemplate>
            <DxToolbar Title="Pending Tasks" />
        </ToolbarTemplate>
    </DxGrid>
</div>

@code {
    ITreeList PlannedTasksTreeList { get; set; }

    DxTreeListDataColumn TreeList_NameDataColumn { get; set; }
    DxGridDataColumn Grid_NameDataColumn { get; set; }

    ObservableCollection<EmployeeTask> PlannedTasks { get; set; }
    ObservableCollection<EmployeeTask> PendingTasks { get; set; }

    protected override void OnInitialized() {
        var employeeTasks = EmployeeTaskDataProvider.GenerateData();
        PendingTasks = new ObservableCollection<EmployeeTask>(employeeTasks.Where(t => t.Priority > 0));
        var pendingTaskIds = PendingTasks.Select(t => t.Id).ToHashSet();
        PlannedTasks = new ObservableCollection<EmployeeTask>(employeeTasks.Where(t => t.Priority <= 0 && !pendingTaskIds.Contains(t.ParentId)));
    }

    void TreeList_ItemsDropped(TreeListItemsDroppedEventArgs evt) {
        var sourceTasks = GetTaskCollection(evt.SourceComponent);
        RemoveDroppedItems(sourceTasks, evt.DroppedItems);

        var targetTask = (EmployeeTask)evt.TargetItem;
        var index = targetTask != null
            ? PlannedTasks.IndexOf(targetTask) + (evt.DropPosition == TreeListItemDropPosition.After ? 1 : 0)
            : PlannedTasks.Count;

        var droppedTasks = evt.DroppedItems.OfType<EmployeeTask>();
        foreach(var droppedTask in droppedTasks) {
            droppedTask.ParentId = evt.DropPosition == TreeListItemDropPosition.Inside
                ? targetTask.Id
                : targetTask.ParentId;
        }

        InsertDroppedItems(PlannedTasks, evt.DroppedItems, index);
    }

    void Grid_ItemsDropped(GridItemsDroppedEventArgs evt) {
        var sourceTasks = GetTaskCollection(evt.SourceComponent);
        RemoveDroppedItems(sourceTasks, evt.DroppedItems);

        var targetTask = (EmployeeTask)evt.TargetItem;
        var index = targetTask != null
            ? PendingTasks.IndexOf(targetTask) + (evt.DropPosition == GridItemDropPosition.After ? 1 : 0)
            : PendingTasks.Count;

        InsertDroppedItems(PendingTasks, evt.DroppedItems, index);
    }

    void RemoveDroppedItems(IList<EmployeeTask> employeeTasks, IEnumerable<object> droppedItems) {
        foreach(var item in droppedItems)
            employeeTasks.Remove((EmployeeTask)item);
    }

    void InsertDroppedItems(IList<EmployeeTask> employeeTasks, IEnumerable<object> droppedItems, int index) {
        foreach(var item in droppedItems.Reverse())
            employeeTasks.Insert(index, (EmployeeTask)item);
    }

    ObservableCollection<EmployeeTask> GetTaskCollection(object grid) {
        return grid == PlannedTasksTreeList ? PlannedTasks : PendingTasks;
    }
}

Implements

AllowedDropTarget