Merge kb-gantt-persist-treelist-width-3061 into production (#3079)

* kb(Gantt): add Gantt TreeList width persistance kb

* kb(Gantt): add PR review suggestions

---------

Co-authored-by: IvanDanchev <ifujin@gmail.com>

Author: github-actions[bot]

knowledge-base/gantt-persist-treelist-width-after-refresh.md

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+---
+title: Persist Gantt TreeList after Refresh
+description: How to persist the width of the Gantt's treelist after refreshing its data?
+type: how-to
+page_title: How to Display Model Fields in the Gantt Tooltip?
+slug: gantt-kb-persist-treelist-width-after-refresh
+tags: gantt, blazor, treelist, width
+res_type: kb
+ticketid: 1690467
+---
+
+## Environment
+<table>
+	<tbody>
+		<tr>
+			<td>Product</td>
+			<td>Gantt for Blazor</td>
+		</tr>
+	</tbody>
+</table>
+
+## Description
+
+If I resize the TreeList part of the Gantt, it gets back to its initial width, after I refresh the Gantt's data. How can I persist the current TreeList width?
+
+## Solution
+
+To persist the current TreeList width, follow the steps below:
+
+1. Bind the `TreeListWidth` parameter of the Gantt to a property. In the example below, the property is named `ListWidth`.
+2. In the methods that manipulate the data of the Gantt (`AddRootTask` and `RemoveTask`), use JavaScript interop to invoke a function. The logic in the function gets and returns the current width of the TreeList.  
+3. Use the current width value to update the value of the `ListWidth` property, before refreshing the data by calling `.Rebind()`.
+
+````RAZOR
+@inject IJSRuntime JS
+
+<TelerikButton OnClick="@AddRootTask">Add root task</TelerikButton>
+
+<TelerikButton OnClick="@RemoveTask">Remove Task 1</TelerikButton>
+
+<TelerikGantt @ref="@GanttRef"
+              Data="@GanttData"
+              @bind-View="@SelectedView"
+              Width="1000px"
+              TreeListWidth="@ListWidth"
+              Height="600px"
+              IdField="Id"
+              ParentIdField="ParentId"
+              OnUpdate="@UpdateItem"
+              OnDelete="@DeleteItem">
+    <GanttColumns>
+        <GanttColumn Field="Title"
+                     Expandable="true"
+                     Width="150px"
+                     Title="Task Title">
+        </GanttColumn>
+        <GanttColumn Field="PercentComplete"
+                     Title="Status"
+                     Width="60px">
+        </GanttColumn>
+        <GanttColumn Field="Start"
+                     Width="90px"
+                     DisplayFormat="{0:d}">
+        </GanttColumn>
+        <GanttColumn Field="End"
+                     Width="90px"
+                     DisplayFormat="{0:d}">
+        </GanttColumn>
+    </GanttColumns>
+    <GanttViews>
+        <GanttDayView></GanttDayView>
+        <GanttWeekView></GanttWeekView>
+        <GanttMonthView></GanttMonthView>
+    </GanttViews>
+</TelerikGantt>
+
+<script suppress-error="BL9992">
+    function getListSize() {
+       var listWidth = document.querySelector('.k-gantt .k-treelist').offsetWidth;
+       return listWidth + "px";
+    }
+</script>
+
+@code {
+    private TelerikGantt<FlatModel>? GanttRef { get; set; }
+    private string ListWidth { get; set; } = "390px";
+    private int LastId { get; set; } = 1;
+    private List<FlatModel> GanttData { get; set; }
+    private GanttView SelectedView { get; set; } = GanttView.Week;
+
+    private async Task AddRootTask()
+    {
+        var i = GanttData.Last().Id + 1;
+
+        GanttData.Insert(0, new FlatModel()
+        {
+            Id = i,
+            ParentId = null,
+            Title = "new task",
+            PercentComplete = 0,
+            Start = new DateTime(2021, 7, 5),
+            End = new DateTime(2021, 7, 15)
+        });
+
+        var currentListWidth = await JS.InvokeAsync<string>("getListSize");
+        ListWidth = currentListWidth;
+
+        GanttRef?.Rebind();
+    }
+
+    private async Task RemoveTask()
+    {
+        var taskToRemove = GanttData.FirstOrDefault(x => x.Title == "Task 1");
+
+        GanttData.Remove(taskToRemove);
+
+        var currentListWidth = await JS.InvokeAsync<string>("getListSize");
+        ListWidth = currentListWidth;
+
+        GanttRef?.Rebind();
+    }
+
+    
+    private void UpdateItem(GanttUpdateEventArgs args)
+    {
+        var item = args.Item as FlatModel;
+
+        var foundItem = GanttData.FirstOrDefault(i => i.Id.Equals(item.Id));
+
+        if (foundItem != null)
+        {
+            foundItem.Title = item.Title;
+            foundItem.Start = item.Start;
+            foundItem.End = item.End;
+            foundItem.PercentComplete = item.PercentComplete;
+        }
+    }
+
+    private void DeleteItem(GanttDeleteEventArgs args)
+    {
+        var item = GanttData.FirstOrDefault(i => i.Id.Equals((args.Item as FlatModel).Id));
+
+        RemoveChildRecursive(item);
+    }
+
+    private void RemoveChildRecursive(FlatModel item)
+    {
+        var children = GanttData.Where(i => item.Id.Equals(i.ParentId)).ToList();
+
+        foreach (var child in children)
+        {
+            RemoveChildRecursive(child);
+        }
+
+        GanttData.Remove(item);
+    }
+
+    protected override void OnInitialized()
+    {
+        GanttData = new List<FlatModel>();
+
+        for (int i = 1; i < 6; i++)
+        {
+            var newItem = new FlatModel()
+            {
+                Id = LastId,
+                Title = "Task " + i.ToString(),
+                Start = new DateTime(2021, 7, 5 + i),
+                End = new DateTime(2021, 7, 11 + i),
+                PercentComplete = Math.Round(Random.Shared.NextDouble(), 2)
+            };
+
+            GanttData.Add(newItem);
+            var parentId = LastId;
+            LastId++;
+
+            for (int j = 0; j < 5; j++)
+            {
+                GanttData.Add(new FlatModel()
+                {
+                    Id = LastId,
+                    ParentId = parentId,
+                    Title = "    Task " + i + " : " + j.ToString(),
+                    Start = new DateTime(2021, 7, 5 + j),
+                    End = new DateTime(2021, 7, 6 + i + j),
+                    PercentComplete = Math.Round(Random.Shared.NextDouble(), 2)
+                });
+
+                LastId++;
+            }
+        }
+
+        base.OnInitialized();
+    }
+
+    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; }
+    }
+}
+````
+
+## See Also
+
+- [Gantt Overview - Telerik UI for Blazor](slug:gantt-overview)