DxTreeList.ItemsDropped Event

Fires when a user drops rows onto the TreeList.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v24.2.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
public EventCallback<TreeListItemsDroppedEventArgs> ItemsDropped { get; set; }

Parameters

Type	Description
TreeListItemsDroppedEventArgs	An object that stores event information.

Remarks

The ItemsDropped event fires when users drop rows onto the TreeList (AllowedDropTarget). In the event handler, update the data source: insert rows at the drop position and remove them from the initial position, if required.

Note that the DroppedItems event argument contains rows in the order they are displayed in the component. If you enable virtual scrolling, the DroppedItems collection contains rows in the order they were selected.

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

<DxTreeList @ref="PlannedTasksTreeList"
            Data="PlannedTasks"
            KeyFieldName="Id"
            ParentKeyFieldName="ParentId"
            AllowDragRows="true"
            AllowedDropTarget="TreeListAllowedDropTarget.All"
            ItemsDropped="TreeList_ItemsDropped">
    <Columns>
        <DxTreeListDataColumn FieldName="Name" Caption="Task" />
        <DxTreeListDataColumn FieldName="Priority" Width="100px" CaptionAlignment="TreeListTextAlignment.Center" TextAlignment="TreeListTextAlignment.Center">
            <CellDisplayTemplate>
                @GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItem)
            </CellDisplayTemplate>
        </DxTreeListDataColumn>
    </Columns>
    <DragHintTextTemplate>
        @if(context.DataItems[0] != null) {
            var employeeTask = (EmployeeTask)context.DataItems[0];
            <span class="dxbl-text">@(employeeTask.Name)</span>
            <span class="dxbl-text">@GetEmployeeTaskPriorityIconHtml(employeeTask)</span>
        }
    </DragHintTextTemplate>
</DxTreeList>

<DxGrid Data="PendingTasks"
        TextWrapEnabled="false"
        AllowDragRows="true"
        AllowedDropTarget="GridAllowedDropTarget.External"
        ItemsDropped="Grid_ItemsDropped">
    <Columns>
        <DxGridDataColumn FieldName="Name" Caption="Task" />
        <DxGridDataColumn FieldName="Priority" Width="100px" CaptionAlignment="GridTextAlignment.Center" TextAlignment="GridTextAlignment.Center">
            <CellDisplayTemplate>
                @GetEmployeeTaskPriorityIconHtml((EmployeeTask)context.DataItem)
            </CellDisplayTemplate>
        </DxGridDataColumn>
    </Columns>
    <DragHintTextTemplate>
        @if(context.DataItems.Count == 1) {
            var employeeTask = (EmployeeTask)context.DataItems[0];
            <span class="dxbl-text">@(employeeTask.Name)</span>
            <span class="dxbl-text">@GetEmployeeTaskPriorityIconHtml(employeeTask)</span>
        }
        else {
            <span class="dxbl-text">@(context.DataItems.Count) tasks</span>
        }
    </DragHintTextTemplate>
</DxGrid>

@code {
    ITreeList PlannedTasksTreeList { get; set; }

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

    protected override async Task OnInitializedAsync() {
        var employeeTasks = EmployeeTaskDataProvider.GenerateData();
        PlannedTasks = new ObservableCollection<EmployeeTask>(employeeTasks.Where(t => t.Priority <= 0));
        PendingTasks = new ObservableCollection<EmployeeTask>(employeeTasks.Where(t => t.Priority > 0));
    }

    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;
    }

    MarkupString GetEmployeeTaskPriorityIconHtml(EmployeeTask employeeTask) {
        var displayText = TreeListRenderHelper.EmployeeTaskPriorityToString(employeeTask);
        var badgeClass = employeeTask.Priority switch {
            -1 => "bg-success",
            0 => "bg-info",
            1 => "bg-warning",
            _ => throw new ArgumentException()
        };

        string html = string.Format("<span class='badge {0} py-1 px-2' title='{1} priority'>{1}</span>", badgeClass, displayText);
        return new MarkupString(html);
    }
}