Added new kb article grid-expand-collapse-multilevel-hierarchy

knowledge-base/grid-expand-collapse-multilevel-hierarchy.md

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+---
+title: Expand and Collapse All Rows in a Multi-Level Hierarchical Grid
+description: Learn how to implement an "Expand/Collapse All" option for a multi-level Hierarchical Grid in Blazor applications.
+type: how-to
+page_title: How to Implement Expand/Collapse All for Multi-Level Hierarchical Grid in Blazor
+slug: grid-kb-expand-collapse-multilevel-hierarchy
+tags: grid, hierarchical, grid, expand, collapse, blazor, state,multilevel
+res_type: kb
+ticketid: 1675753
+---
+
+## Description
+
+In a multi-level Hierarchical Grid structure, it is common to require functionality that allows users to expand or collapse all parent, child, and grandchild rows with a single action. This article demonstrates how to implement an "Expand/Collapse All" button for a Blazor application that controls the expansion state of all rows in a three-level hierarchical grid structure: Parent Grid -> Child Grid -> Grand Child Grid.
+
+## Solution
+
+To control the expansion and collapse of all rows in a multi-level Hierarchical Grid, utilize the [Grid State](slug://grid-state).
+
+1. Use the [`SetStateAsync` method](slug://grid-state#methods) for the parent Grid to control the expansion and collapse of its rows.
+2. Use the [`OnStateInit` event](slug://grid-state#onstateinit) of the child Grids to expand their rows by default when the parent Grid rows expand.
+3. If some child Grids are already visible and their `OnStateInit` event has been fired, use `SetStateAsync` for these child Grids to control their expansion state.
+
+````RAZOR
+<TelerikGrid @ref="@GridRef"
+             Data="@GridData">
+    <GridToolBarTemplate>
+        <GridCommandButton OnClick="@OnExpandAllClick">Expand All</GridCommandButton>
+        <GridCommandButton OnClick="@OnCollapseAllClick">Collapse All</GridCommandButton>
+    </GridToolBarTemplate>
+    <GridColumns>
+        <GridColumn Field="@nameof(SampleModel.Name)" />
+    </GridColumns>
+    <DetailTemplate Context="masterItem">
+        <TelerikGrid Data="@ChildGridData.Where(x => x.ParentId == masterItem.Id)"
+                     OnStateInit="@( (GridStateEventArgs<SampleModel> args) => OnChildGridStateInit(args, masterItem.Id))">
+            <GridColumns>
+                <GridColumn Field="@nameof(SampleModel.Name)" />
+            </GridColumns>
+            <DetailTemplate Context="childItem">
+                <TelerikGrid Data="@GrandChildGridData.Where(x => x.ParentId == childItem.Id)">
+                    <GridColumns>
+                        <GridColumn Field="@nameof(SampleModel.Name)" />
+                    </GridColumns>
+                </TelerikGrid>
+            </DetailTemplate>
+        </TelerikGrid>
+    </DetailTemplate>
+</TelerikGrid>
+
+@code {
+    private TelerikGrid<SampleModel>? GridRef { get; set; }
+    private List<SampleModel> GridData { get; set; } = new();
+    private List<SampleModel> ChildGridData { get; set; } = new();
+    private List<SampleModel> GrandChildGridData { get; set; } = new();
+
+    private async Task OnCollapseAllClick()
+    {
+        var gridState = GridRef!.GetState();
+
+        gridState.ExpandedItems = new List<SampleModel>();
+
+        await GridRef.SetStateAsync(gridState);
+    }
+
+    private async Task OnExpandAllClick()
+    {
+        var gridState = GridRef!.GetState();
+
+        gridState.ExpandedItems = new List<SampleModel>(GridData);
+
+        await GridRef.SetStateAsync(gridState);
+    }
+
+    private void OnChildGridStateInit(GridStateEventArgs<SampleModel> args, int masterId)
+    {
+        args.GridState.ExpandedItems = ChildGridData.Where(x => x.ParentId == masterId).ToList();
+    }
+
+    protected override void OnInitialized()
+    {
+        for (int i = 1; i <= 2; i++)
+        {
+            GridData.Add(new SampleModel()
+            {
+                Id = i,
+                Name = $"Name {i}"
+            });
+
+            for (int j = 1; j <= 2; j++)
+            {
+                ChildGridData.Add(new SampleModel()
+                {
+                    Id = 100 * i + j,
+                    ParentId = i,
+                    Name = $"Name {100 * i + j}"
+                });
+
+                for (int k = 1; k <= 2; k++)
+                {
+                    GrandChildGridData.Add(new SampleModel()
+                    {
+                        Id = 1000 * i + 100 * j + k,
+                        ParentId = 100 * i + j,
+                        Name = $"Name {1000 * i + 100 * j + k}"
+                    });
+
+                }
+            }
+        }
+    }
+
+    public class SampleModel
+    {
+        public int Id { get; set; }
+        public int? ParentId { get; set; }
+        public string Name { get; set; } = string.Empty;
+    }
+}
+````
+
+## See Also
+
+* [Grid State Documentation](slug://grid-state)
+* [Nesting Render Fragments in Blazor](slug://nest-renderfragment)
+* [Dynamic References in Blazor](slug://common-kb-dynamic-refs)