fix: SetTotalItemCountAsync in PaginationState

[vpetit-reimagine]

🐛 Bug Report

Using FluentDataGrid with PaginationState and a list of items results in the PaginationState using the count of the retrieved Queryable as the TotalItemCount instead of the value assigned via SetTotalItemCountAsync

💻 Repro or Code Sample

@using System.Web
@using Microsoft.FluentUI.AspNetCore.Components


<FluentDataGrid @ref="_myGrid" TGridItem="MyItem" Items="_items" 
                GridTemplateColumns="35px" 
                ResizableColumns="false" Pagination="@_pagination">
        
    <PropertyColumn Property="@(s => s.Id)" Title="ID"></PropertyColumn>
</FluentDataGrid>
    
<FluentPaginator State="@_pagination" CurrentPageIndexChanged="() => LoadItemsWithFiltering()"/>

@code {
    public class MyItem {
        public long Id { get; set; }
    }

    private IQueryable<MyItem> _items;
    
    private int _count;
    
    private PaginationState _pagination = new();
    private FluentDataGrid<SignalOverviewDto> _myGrid;

    protected override void OnInitialized()
    {
        base.OnInitialized();
        
        _pagination.TotalItemCountChanged += (sender, eventArgs) => StateHasChanged();
    }

    protected override async Task OnParametersSetAsync()
    {
        await base.OnParametersSetAsync();

        await LoadItemsWithFiltering();
    }

    private async Task LoadItemsWithFiltering()
    {
        /* API call here, basically looking like: */
        _items = await _myItemService.ListItems(_pagination.CurrentPageIndex * _pagination.ItemsPerPage, _pagination.ItemsPerPage);
        _count = await _myItemService.CountItems();

        // Fails here: The call sets it to 20 but it is then set to the number of items in the IQueryable
        await _pagination.SetTotalItemCountAsync(_count); 
        await InvokeAsync(StateHasChanged);
    }
}

Steps to reproduce:

1. Load data in the Data Grid with Items="_items"
2. Manually update the PaginationState with SetTotalItemCountAsync
3. The TotalItemCount is set to the number of items in the IQueryable

🤔 Expected Behavior

The TotalItemCount should be the value I assign it to, as I currently fetch a small list of items instead of everything

😯 Current Behavior

For some reason, the method SetTotalItemCountAsync just does something strange (probably the callbacks behind that are doing stuff that are not expected).

💁 Possible Solution

Allow the SetTotalItemCountAsync to override the count of the IQueryable

🔦 Context

I'm trying to load the items of a db call with pagination outside of the ItemsProvider because that has way too many other issues to start looking into.

🌍 Your Environment

• OS & Device: Windows, PC
• Browser: Firefox Developer Edition
• .NET 8.0.2, FluentUI Components 4.9.3

[vpetit-reimagine]

I found out that if I use the FluentPaginator and the PaginationState "outside" of the FluentDataGrid I can actually use the SetTotalItemCountAsync. It might be worth mentioning that on the documentation as an alternative in case someone wants to use the pagination with a partial list of items. (I just removed the Pagination="@_pagination" part of the DataGrid).

[vnbaaij]

When using Items, the total count is always based on that collection by design. This seems quite logical to me. Normally if you use items, the set of 'records' you work with is known. If not, you can use the ItemsProvider.

I'll add a note to the documentation on your finding about using them separately.

[vpetit-reimagine]

From what I've read in the documentation, that was logical to me as well that ItemsProvider should be the way to go for this use case. However, as you mention in other issues/discussions, the FluentDataGrid is free to redraw the UI as it pleases when using the ItemsProvider. Sadly, doing so prevent it to be used with <SelectColumn> templates and/or inner buttons in the grid as any interaction with it redraws it (losing the selected state, current scrolling).

This is why I had to go for the Items option.

[vnbaaij]

This has been addressed by #2530