@using Telerik.DataSource
@using Telerik.DataSource.Extensions

Scroll through the groups or expand them to load their data on demand

<TelerikGrid TItem="@object"
             LoadGroupsOnDemand="true"
             Groupable="true"
             OnStateInit="@((GridStateEventArgs<object> args) => OnStateInitHandler(args))"
             OnRead="@ReadItems"
             ScrollMode="@GridScrollMode.Virtual" PageSize="20" RowHeight="60"
             Navigable="true" Sortable="true" FilterMode="@GridFilterMode.FilterRow" Height="600px">
    <GridColumns>
        <GridColumn Field="@nameof(Employee.Name)" FieldType="@typeof(string)" Groupable="false" />
        <GridColumn Field="@nameof(Employee.Team)" FieldType="@typeof(string)" Title="Team" />
        <GridColumn Field="@nameof(Employee.Salary)" FieldType="@typeof(decimal)" Groupable="false" />
        <GridColumn Field="@nameof(Employee.IsOnLeave)" FieldType="@typeof(bool)" Title="On Vacation" />
    </GridColumns>
</TelerikGrid>

@code {
    List<object> GridData { get; set; }

    protected async Task ReadItems(GridReadEventArgs args)
    {
        // sample data retrieval, see comments in the service mimic class below
        DataEnvelope<Employee> result = await MyService.GetData(args.Request);

        if (args.Request.Groups.Count > 0)
        {
            args.Data = result.GroupedData.Cast<object>().ToList();
        }
        else
        {
            args.Data = result.CurrentPageData.Cast<object>().ToList();
        }

        args.Total = result.TotalItemCount;
    }

    void OnStateInitHandler(GridStateEventArgs<object> args)
    {
        // set initial grouping
        GridState<object> desiredState = new GridState<object>()
        {
            GroupDescriptors = new List<GroupDescriptor>()
            {
                new GroupDescriptor()
                {
                    Member = "Team",
                    MemberType = typeof(string)
                },
                new GroupDescriptor()
                {
                    Member = "IsOnLeave",
                    MemberType = typeof(bool)
                }
            }
        };

        args.GridState = desiredState;
    }

    public class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public string? Team { get; set; }
        public bool IsOnLeave { get; set; }
        public decimal Salary { get; set; }
    }

    public class DataEnvelope<T>
    {
        public List<AggregateFunctionsGroup> GroupedData { get; set; }
        public List<T> CurrentPageData { get; set; }
        public int TotalItemCount { get; set; }
    }

    public static class MyService
    {
        private static List<Employee> SourceData { get; set; }
        public static async Task<DataEnvelope<Employee>> GetData(DataSourceRequest request)
        {
            if (SourceData == null)
            {
                SourceData = new List<Employee>();
                var rand = new Random();
                for (int i = 1; i <= 3; i++)
                {
                    SourceData.Add(new Employee()
                    {
                        EmployeeId = i,
                        Name = "Employee " + i.ToString(),
                        Team = "Team " + i % 100,
                        IsOnLeave = i % 3 == 0,
                        Salary = rand.Next(1000, 5000)
                    });
                }
                SourceData.Add(new Employee()
                    {
                        EmployeeId = 3,
                        Name = "Employee " + 3.ToString(),
                        Team = null,
                        IsOnLeave = 3 % 3 == 0,
                        Salary = rand.Next(1000, 5000)
                    });
            }

            await Task.Delay(500);// deliberate delay to showcase async operations, remove in a real app

            // retrieve data as needed, you can find more examples and runnable projects here
            // https://github.com/telerik/blazor-ui/tree/master/grid/datasourcerequest-on-server
            var datasourceResult = SourceData.ToDataSourceResult(request);

            DataEnvelope<Employee> dataToReturn;

            if (request.Groups.Count > 0)
            {
                dataToReturn = new DataEnvelope<Employee>
                {
                    GroupedData = datasourceResult.Data.Cast<AggregateFunctionsGroup>().ToList(),
                    TotalItemCount = datasourceResult.Total
                };
            }
            else
            {
                dataToReturn = new DataEnvelope<Employee>
                {
                    CurrentPageData = datasourceResult.Data.Cast<Employee>().ToList(),
                    TotalItemCount = datasourceResult.Total
                };
            }

            return await Task.FromResult(dataToReturn);
        }
    }
}

The following code successfully renders the pdf viewer when the edit form is commented out, but when indside the pdf viewer it fails to render and gives the following error:
"Telerik.Blazor.Components.TelerikComboBox`2[Telerik.Blazor.Components.PdfViewer.Models.PdfViewerZoomLevelDescriptor,System.String] requires a value for the 'ValueExpression' ValueExpression is provided automatically when using 'bind-Value'.See more at https://docs.telerik.com/blazor-ui/knowledge-base/requires-valueexpression ."
 
 
@page "/pdfBug"

@* <EditForm Model="_fakeContext"> *@
    <TelerikPdfViewer Data="@PdfSource"
                      OnDownload="@OnPdfDownload"
                      Height="600px"></TelerikPdfViewer>
@* </EditForm> *@

@code {
    private byte[] PdfSource { get; set; }

    private async Task OnPdfDownload(PdfViewerDownloadEventArgs args)
    {
        args.FileName = "PDF-Viewer-Download";
    }

    protected override void OnInitialized()
    {
        PdfSource = Convert.FromBase64String(PdfBase64);

        base.OnInitialized();
    }

        private const string PdfBase64 = "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";
    private FakeContext _fakeContext = new FakeContext() { Name = "Test" };
    public class FakeContext
    {
        public string Name { get; set; }
    }
}
    

@page "/"
@using TelerikBlazorTestApp.Models

<TelerikScheduler Data="@Appointments" 
                  AllowCreate="true" AllowDelete="true" AllowUpdate="true"
                  OnModelInit="@ModelInitHandler">
    <SchedulerViews>
        <SchedulerDayView />
        <SchedulerWeekView />
        <SchedulerMonthView />
    </SchedulerViews>
</TelerikScheduler>

@code {
    public List<SchedulerAppointment<TestModel>> Appointments { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Appointments = new List<SchedulerAppointment<TestModel>>()
        {
             new SchedulerAppointment<TestModel> { Title = "Test 1", Start = DateTime.Now, End = DateTime.Now.AddHours(1), IsAllDay = false, Model =  new TestModel("blah") },
             new SchedulerAppointment<TestModel> { Title = "Test 2", Start = DateTime.Now.AddHours(1), End = DateTime.Now.AddHours(2), IsAllDay = false, Model =  new TestModel("blah") },
             new SchedulerAppointment<TestModel> { Title = "Test 3", Start = DateTime.Now, End = DateTime.Now, IsAllDay = true, Model =  new TestModel("blah") }
        };
    }

    public SchedulerAppointment<TestModel> ModelInitHandler()
    {
        return new SchedulerAppointment<TestModel>("blah");
    }
}

namespace TelerikBlazorTestApp.Models
{
    public class SchedulerAppointment<TItem>
    {
        public Guid Id { get; set; }
        public string Title { get; set; }
        public string Description { get; set; }
        public DateTime Start { get; set; }
        public DateTime End { get; set; }
        public bool IsAllDay { get; set; }
        public string RecurrenceRule { get; set; }
        public List<DateTime> RecurrenceExceptions { get; set; }
        public Guid? RecurrenceId { get; set; }

        public TItem Model { get; set; }

        public SchedulerAppointment()
        {
            Id = Guid.NewGuid();
        }

        public SchedulerAppointment(string s)
        {
            Id = Guid.NewGuid();
            Model = (TItem)Activator.CreateInstance(typeof(TItem), s);
        }
    }
}

namespace TelerikBlazorTestApp.Models
{
    public class TestModel
    {
        public string PropA { get; set; }
        public string PropB { get; set; }

        public TestModel(string s)
        {
            // something using s here
        }
    }
}