@using System.Collections.ObjectModel

<TelerikGrid @ref="@Grid"
             Data="@GridData"
             SelectionMode="@GridSelectionMode.Single"
             OnRowClick="@OnRowClickHandler"
             @bind-SelectedItems="@SelectedData"
             EditMode="@GridEditMode.Incell"
             Resizable="true"
             Width="100%"
             Height="200px"
             Reorderable="true"
             Groupable="false"
             ShowColumnMenu="false"
             FilterMode="@GridFilterMode.None"
             Sortable="true">
    <GridColumns>
        <GridColumn Field=@nameof(ViewModel.Name) Editable="false">
        </GridColumn>
    </GridColumns>
</TelerikGrid>

<TelerikButton OnClick="RefreshButtonClick">Refresh</TelerikButton>

@code {
    private const int RowHeight = 40;
    private const string Height = "700px";
    private const int PageSize = 20;

    private ObservableCollection<ViewModel> GridData { get; set; } = new ObservableCollection<ViewModel>();
    private IEnumerable<ViewModel> SelectedData { get; set; } = Enumerable.Empty<ViewModel>();

    private TelerikGrid<ViewModel> Grid { get; set; }

    protected override async Task OnInitializedAsync()
    {
        await LoadData();

        await base.OnInitializedAsync();
    }

    async Task LoadData()
    {
        var data = Enumerable.Range(1, 5).Select(x => new ViewModel { Name = $"name {x}" });
        GridData = new ObservableCollection<ViewModel>(data);
    }


    private async Task RefreshButtonClick()
    {
        Console.WriteLine("reload data");

        // spawn a new thread, a Timer will do as well
        await Task.Run(() =>
        {
            IEnumerable<ViewModel> data = new List<ViewModel> { new ViewModel { Name = "1" }, new ViewModel { Name = "2" }, new ViewModel { Name = "3" } };

            this.GridData.Clear();
            this.GridData.AddRange(data);
        });
    }

    private void OnRowClickHandler(GridRowClickEventArgs args)
    {
        Console.WriteLine("click to select");
        ViewModel viewModel = (ViewModel)args.Item;
        //this is here because of theincell editing, not relevant to the issue
        SelectedData = new List<ViewModel>() { viewModel };
    }

    public class ViewModel
    {
        public ViewModel()
        {
        }

        private string name;
        public string Name
        {
            get
            {
                return name;
            }
            set
            {
                name = value;
            }
        }
    }
}

@using System.ComponentModel.DataAnnotations
@* Used for the model annotations only *@

<strong>REPRO: activate the validation for the Name field to see the issue - click Save with an empty input</strong>

<TelerikGrid Data=@MyData EditMode="@GridEditMode.Popup" Pageable="true" Height="500px"
             OnUpdate="@UpdateHandler" OnDelete="@DeleteHandler" OnCreate="@CreateHandler">
    <GridToolBar>
        <GridCommandButton Command="Add" Icon="add">Add Employee</GridCommandButton>
    </GridToolBar>
    <GridColumns>
        <GridColumn Field=@nameof(SampleData.ID) Title="ID" Editable="false" />
        <GridColumn Field=@nameof(SampleData.Name) Title="Name" />
        <GridCommandColumn>
            <GridCommandButton Command="Save" Icon="save" ShowInEdit="true">Update</GridCommandButton>
            <GridCommandButton Command="Edit" Icon="edit">Edit</GridCommandButton>
            <GridCommandButton Command="Delete" Icon="delete">Delete</GridCommandButton>
            <GridCommandButton Command="Cancel" Icon="cancel" ShowInEdit="true">Cancel</GridCommandButton>
        </GridCommandColumn>
    </GridColumns>
</TelerikGrid>

@code {

    public class SampleData
    {
        public int ID { get; set; }

        [Required(ErrorMessage = "aa something else")] // the first word is 1 or 2 characters to show the issue
        public string Name { get; set; }
    }

    async Task UpdateHandler(GridCommandEventArgs args)
    {
        SampleData item = (SampleData)args.Item;

        // perform actual data source operations here through your service

        // if the grid Data is not tied to the service, you may need to update the local view data too
        var index = MyData.FindIndex(i => i.ID == item.ID);
        if (index != -1)
        {
            MyData[index] = item;
        }
    }

    async Task DeleteHandler(GridCommandEventArgs args)
    {
        SampleData item = (SampleData)args.Item;

        // perform actual data source operation here through your service

        // if the grid Data is not tied to the service, you may need to update the local view data too
        MyData.Remove(item);
    }

    async Task CreateHandler(GridCommandEventArgs args)
    {
        SampleData item = (SampleData)args.Item;

        // perform actual data source operation here through your service

        // if the grid Data is not tied to the service, you may need to update the local view data too
        item.ID = MyData.Count + 1;
        MyData.Insert(0, item);
    }


    public List<SampleData> MyData { get; set; }

    protected override void OnInitialized()
    {
        MyData = new List<SampleData>();

        for (int i = 0; i < 50; i++)
        {
            MyData.Add(new SampleData()
            {
                ID = i,
                Name = "Name " + i.ToString()
            });
        }
    }
}

@using Telerik.Blazor
@using Telerik.Blazor.Components.Grid

<TelerikGrid Data=@GridData
             SelectionMode="GridSelectionMode.Multiple"
             @bind-SelectedItems="SelectedItems"
             Pageable="true"
             Height="400px">
    <TelerikGridToolBar>
        <TelerikGridCommandButton Command="MyDelete" OnClick="DeleteSelectedAsync"
                                         Enabled=@(SelectedItems?.Count() > 0) Icon="delete">Delete</TelerikGridCommandButton>
        <TelerikGridCommandButton Enabled="false" OnClick="DeleteSelectedAsync">I must always be disabled</TelerikGridCommandButton>
</TelerikGridToolBar>
    <TelerikGridColumns>
        <TelerikGridCheckboxColumn />
        <TelerikGridColumn Field=@nameof(Employee.Name) />
        <TelerikGridColumn Field=@nameof(Employee.Team) Title="Team" />
    </TelerikGridColumns>
</TelerikGrid>

@result

@if (SelectedItems != null)
{
    <ul>
        @foreach (Employee employee in SelectedItems)
        {
            <li>
                @employee.Name
            </li>
        }
    </ul>
}

@code {
    void DeleteSelectedAsync()
    {
        result = $"On {DateTime.Now} there are {SelectedItems?.Count()} items selected";
    }
    string result;

    public List<Employee> GridData { get; set; }
    public IEnumerable<Employee> SelectedItems { get; set; }

    protected override void OnInitialized()
    {
        GridData = new List<Employee>();
        for (int i = 0; i < 15; i++)
        {
            GridData.Add(new Employee()
            {
                EmployeeId = i,
                Name = "Employee " + i.ToString(),
                Team = "Team " + i % 3
            });
        }

        // select Employee with 3 through 5
        SelectedItems = GridData.Skip(2).Take(3).ToList();
    }

    public class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public string Team { get; set; }
    }
}

@using Telerik.DataSource.Extensions

@*  workaround:  *@

@*Page="@GridPage"
PageChanged="@OnGridPageChanged"*@

<TelerikGrid OnRead="@OnGridRead"
             Navigable="true"
             TItem="@Product"
             Pageable="true">
    <GridColumns>
        <GridColumn Field="@nameof(Product.Name)" Title="Product Name" />
    </GridColumns>
</TelerikGrid>

@code {
    List<Product> GridData { get; set; }
    int GridPage { get; set; } = 1;
    int GridTotal { get; set; }

    // workaround
    void OnGridPageChanged(int newPage)
    {
        if (newPage > 0 && newPage <= Math.Ceiling((double)GridTotal / (double)10))
        {
            GridPage = newPage;
        }
    }

    void OnGridRead(GridReadEventArgs args)
    {
        var result = GridData.ToDataSourceResult(args.Request);

        args.Data = result.Data;
        args.Total = result.Total;

        // workaround
        //GridTotal = result.Total;
    }

    protected override void OnInitialized()
    {
        GridData = new List<Product>();
        var rnd = new Random();

        for (int i = 1; i <= 12; i++)
        {
            GridData.Add(new Product()
            {
                Id = i,
                Name = "Product " + i.ToString()
            });
        }
    }

    public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

Error: System.ArgumentException: Page Size cannot be less than one (Parameter 'PageSize')