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Gantt Events

This article explains the events available in the Telerik Gantt for Blazor. They are grouped logically.

CUD Events

The OnCreate, OnUpdate and OnDelete events lets you get the data item that the user changed so you can transfer the user action to the actual data source.

The OnEdit event lets you respond to user actions when they want to edit an item. For example, you can use it to prevent editing of certain items based on some condition.

You can read more about the CUD events in the Gantt Tree Editing Overview article.

TreeListWidthChanged

The TreeListWidthChanged event fires as a response to the user changing the width of the TreeList pane in the splitter.

OnExpand and OnCollapse

The OnExpand and OnCollapse events fire as a response to the user expanding and collapsing an item of the Gant Tree.

The event handlers receive arguments of type GanttExpandEventArgs and GanttCollapseEventArgs respectively which exposes the following fields:

  • Item - an object you can cast to your model class to obtain the current data item.
  • ShouldRender - a boolean field indicating whether the component will re-render.

The OnCollapse event fires as a response to the user collapsing an item of the Gant Tree.

Handle OnExpand and OnCollapse events

@eventActions

<TelerikGantt Data="@Data"
              Width="1200px"
              Height="600px"
              IdField="Id"
              ParentIdField="ParentId"

              OnExpand="@OnItemExpand"
              OnCollapse="@OnItemCollapse"

              OnUpdate="@UpdateItem"
              OnDelete="@DeleteItem"
              OnCreate="@CreateItem">
    <GanttToolBar>
        <GanttCommandButton Command="Add" Icon="add">Add</GanttCommandButton>
    </GanttToolBar>
    <GanttViews>
        <GanttDayView></GanttDayView>
        <GanttWeekView></GanttWeekView>
        <GanttMonthView></GanttMonthView>
        <GanttYearView></GanttYearView>
    </GanttViews>
    <GanttColumns>
        <GanttColumn Field="Id"
                     Visible="false">
        </GanttColumn>
        <GanttColumn Field="Title"
                     Expandable="true"
                     Width="160px"
                     Title="Task Title" >
        </GanttColumn>
        <GanttColumn Field="PercentComplete"
                     Width="60px">
        </GanttColumn>
        <GanttColumn Field="Start"
                     Width="100px"
                     TextAlign="@ColumnTextAlign.Right">
        </GanttColumn>
        <GanttColumn Field="End"
                     DisplayFormat="End: {0:d}"
                     Width="100px">
        </GanttColumn>
        <GanttCommandColumn>
            <GanttCommandButton Command="Add" Icon="add"></GanttCommandButton>
            <GanttCommandButton Command="Delete" Icon="delete"></GanttCommandButton>
        </GanttCommandColumn>
    </GanttColumns>
</TelerikGantt>

@code {
    public DateTime SelectedDate { get; set; } = new DateTime(2019, 11, 11, 6, 0, 0);

    public string eventActions { get; set; }

    class FlatModel
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Title { get; set; }
        public double PercentComplete { get; set; }
        public DateTime Start { get; set; }
        public DateTime End { get; set; }
    }

    public int LastId { get; set; } = 1;
    List<FlatModel> Data { get; set; }

    protected override void OnInitialized()
    {
        Data = new List<FlatModel>();
        var random = new Random();

        for (int i = 1; i < 6; i++)
        {
            var newItem = new FlatModel()
            {
                Id = LastId,
                Title = "Employee  " + i.ToString(),
                Start = new DateTime(2020, 12, 6 + i),
                End = new DateTime(2020, 12, 11 + i),
                PercentComplete = Math.Round(random.NextDouble(), 2)
            };

            Data.Add(newItem);
            var parentId = LastId;
            LastId++;

            for (int j = 0; j < 5; j++)
            {
                Data.Add(new FlatModel()
                {
                    Id = LastId,
                    ParentId = parentId,
                    Title = "    Employee " + i + " : " + j.ToString(),
                    Start = new DateTime(2020, 12, 6 + i + j),
                    End = new DateTime(2020, 12, 7 + i + j),
                    PercentComplete = Math.Round(random.NextDouble(), 2)
                });

                LastId++;
            }
        }

        base.OnInitialized();
    }

    private async Task CreateItem(GanttCreateEventArgs args)
    {
        var argsItem = args.Item as FlatModel;

        argsItem.Id = LastId++;

        if (args.ParentItem != null)
        {
            var parent = (FlatModel)args.ParentItem;

            argsItem.ParentId = parent.Id;
        }

        Data.Insert(0, argsItem);

        CalculateParentPercentRecursive(argsItem);
        CalculateParentRangeRecursive(argsItem);
    }

    private async Task UpdateItem(GanttUpdateEventArgs args)
    {
        var item = args.Item as FlatModel;

        var foundItem = Data.FirstOrDefault(i => i.Id.Equals(item.Id));

        if (foundItem != null)
        {
            var startOffset = item.Start - foundItem.Start;
            if (startOffset != TimeSpan.Zero)
            {
                MoveChildrenRecursive(foundItem, startOffset);
            }

            foundItem.Title = item.Title;
            foundItem.Start = item.Start;
            foundItem.End = item.End;
            foundItem.PercentComplete = item.PercentComplete;
        }

        CalculateParentPercentRecursive(foundItem);
        CalculateParentRangeRecursive(foundItem);
    }

    private async Task DeleteItem(GanttDeleteEventArgs args)
    {
        var item = Data.FirstOrDefault(i => i.Id.Equals((args.Item as FlatModel).Id));

        RemoveChildRecursive(item);

        CalculateParentPercentRecursive(item);
        CalculateParentRangeRecursive(item);
    }

    public void OnItemExpand(GanttExpandEventArgs args)
    {
        var item = args.Item as FlatModel;
        eventActions = $"The user expanded {item.Title} with ID {item.Id}";
    }

    public void OnItemCollapse(GanttCollapseEventArgs args)
    {
        var item = args.Item as FlatModel;
        eventActions = $"The user collapsed {item.Title} with ID {item.Id}";
    }

    private void RemoveChildRecursive(FlatModel item)
    {
        var children = GetChildren(item).ToList();

        foreach (var child in children)
        {
            RemoveChildRecursive(child);
        }

        Data.Remove(item);
    }

    private void CalculateParentPercentRecursive(FlatModel item)
    {
        if (item.ParentId != null)
        {
            var parent = GetParent(item);

            var children = GetChildren(parent);

            if (children.Any())
            {
                parent.PercentComplete = children.Average(i => i.PercentComplete);

                CalculateParentPercentRecursive(parent);
            }
        }
    }

    private void CalculateParentRangeRecursive(FlatModel item)
    {
        if (item.ParentId != null)
        {
            var parent = GetParent(item);

            var children = GetChildren(parent);

            if (children.Any())
            {
                parent.Start = children.Min(i => i.Start);
                parent.End = children.Max(i => i.End);

                CalculateParentRangeRecursive(parent);
            }
        }
    }

    private void MoveChildrenRecursive(FlatModel item, TimeSpan offset)
    {
        var children = GetChildren(item);

        foreach (var child in children)
        {
            child.Start = child.Start.Add(offset);
            child.End = child.End.Add(offset);

            MoveChildrenRecursive(child, offset);
        }
    }

    private FlatModel GetParent(FlatModel item)
    {
        return Data.FirstOrDefault(i => i.Id.Equals(item.ParentId));
    }

    private IEnumerable<FlatModel> GetChildren(FlatModel item)
    {
        return Data.Where(i => item.Id.Equals(i.ParentId));
    }
}

See Also

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