@using Telerik.DataSource

<h2>No Aggregates</h2>

<p><code>OnStateInitCounter1:</code> @OnStateInitCounter1</p>
<TelerikGrid Data="@GridData"
             TItem="@SampleModel"
             Groupable="true"
             OnStateInit="@OnGridStateInit1">
    <GridAggregates>

    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(SampleModel.Name)" />
        <GridColumn Field="@nameof(SampleModel.GroupName)" />
    </GridColumns>
</TelerikGrid>

<h2>With Aggregates</h2>

<p><code>OnStateInitCounter2:</code> @OnStateInitCounter2</p>
<TelerikGrid Data="@GridData"
             TItem="@SampleModel"
             Groupable="true"
             OnStateInit="@OnGridStateInit2">
    <GridAggregates>
        <GridAggregate Field="@nameof(SampleModel.Name)" Aggregate="@GridAggregateType.Count" />
    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(SampleModel.Name)" />
        <GridColumn Field="@nameof(SampleModel.GroupName)" />
    </GridColumns>
</TelerikGrid>

<h2>With Aggregates and Workaround</h2>

<p><code>OnStateInitCounter3:</code> @OnStateInitCounter3</p>
<TelerikGrid Data="@GridData"
             TItem="@SampleModel"
             Groupable="true"
             OnStateInit="@OnGridStateInit3">
    <GridAggregates>
        <GridAggregate Field="@nameof(SampleModel.Name)" Aggregate="@GridAggregateType.Count" />
    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(SampleModel.Name)" />
        <GridColumn Field="@nameof(SampleModel.GroupName)" />
    </GridColumns>
</TelerikGrid>

@code {
    private int OnStateInitCounter1 { get; set; }
    private int OnStateInitCounter2 { get; set; }
    private int OnStateInitCounter3 { get; set; }

    private void OnGridStateInit1(GridStateEventArgs<SampleModel> args)
    {
        ++OnStateInitCounter1;

        args.GridState.GroupDescriptors.Add(new GroupDescriptor
        {
            Member = nameof(SampleModel.GroupName)
        });
    }

    private void OnGridStateInit2(GridStateEventArgs<SampleModel> args)
    {
        ++OnStateInitCounter2;

        args.GridState.GroupDescriptors.Add(new GroupDescriptor
        {
            Member = nameof(SampleModel.GroupName)
        });
    }

    private void OnGridStateInit3(GridStateEventArgs<SampleModel> args)
    {
        ++OnStateInitCounter3;

        args.GridState.GroupDescriptors = new List<GroupDescriptor>();
        // OR
        args.GridState.GroupDescriptors.Clear();

        args.GridState.GroupDescriptors.Add(new GroupDescriptor
        {
            Member = nameof(SampleModel.GroupName)
        });
    }

    private List<SampleModel> GridData { get; set; } = new();

    protected override void OnInitialized()
    {
        for (int i = 1; i <= 4; i++)
        {
            GridData.Add(new SampleModel()
            {
                Id = i,
                Name = $"Name {i}",
                GroupName = $"Group {i % 2 + 1}"
            });
        }
    }

    public class SampleModel
    {
        public int Id { get; set; }
        public string Name { get; set; } = string.Empty;
        public string GroupName { get; set; } = string.Empty;
    }
}