@{
    if (GridColumns.Count() > 0)
    {
        <TelerikGrid Data="@Data">
            <GridColumns>
                @foreach (var column in GridColumns)
                    {
                    <GridColumn Field="@column.DataField"
                                ShowColumnMenu="false" Title="@column.DisplayName" Resizable="true" Width="500px">
                        <FooterTemplate>
                            foo
                        </FooterTemplate>
                    </GridColumn>
                    }
            </GridColumns>
        </TelerikGrid>
    }
}

@using Telerik.Blazor.Common.Export.Excel
@using Telerik.Blazor.Components.Grid

<TelerikGrid TItem="@FlowRun"
             Pageable="true"
             OnRead="@GetData">

    <GridToolBar>
        <GridCommandButton Command="ExcelExport" Icon="file-excel">Export to Excel</GridCommandButton>
        <GridCommandButton Command="CsvExport" Icon="file-csv">Export to CSV</GridCommandButton>
        <label class="k-checkbox-label"><TelerikCheckBox @bind-Value="@ExportAllPages" />Export All Pages</label>
    </GridToolBar>

    <GridExport>
        <GridExcelExport FileName="telerik-grid-export" AllPages="@ExportAllPages" OnBeforeExport="@BeforeExcelExport" />
        <GridCsvExport FileName="telerik-grid-export" AllPages="@ExportAllPages" OnBeforeExport="@BeforeCsvExport" />
    </GridExport>

    <GridColumns>
        <GridColumn Field="@nameof(FlowRun.FileName)" Title="File Name" Width="300px" />
        <GridColumn Field="@nameof(FlowRun.Type)" Title="Type" Width="100px" />
        <GridColumn Field="@nameof(FlowRun.FileSize)" Title="File Size" Width="200px" />
        <GridColumn Title="Source">
            <Columns>
                <GridColumn Field="@(nameof(FlowRun.Source))" Title="MPID"/>
                <GridColumn Field="@(nameof(FlowRun.SourceFileProtocol))" Title="Type" />
            </Columns>
        </GridColumn>
        <GridColumn Field="@nameof(FlowRun.ErrorMessage)"
                    Title = "Error"
                    Width="0" />
    </GridColumns>
</TelerikGrid>

@code {
    bool ExportAllPages { get; set; }

    private async Task GetData(GridReadEventArgs args)
    {
        args.Data = Enumerable.Range(1, 10).Select(x => new FlowRun
            {
                FileName = $"File {x}",
                Type = $"Type {x}",
                FileSize = x * 2,
                Source = $"Source {x}",
                SourceFileProtocol = FileProtocol.CIX,
                ErrorMessage = $"Error {x}"
            }).ToList();

        args.Total = 100;
    }

    private void BeforeCsvExport(GridBeforeCsvExportEventArgs obj)
    {
        AddErrorMessageColumn(obj);
    }

    private void BeforeExcelExport(GridBeforeExcelExportEventArgs obj)
    {
        AddErrorMessageColumn(obj);
    }

    private void AddErrorMessageColumn(GridBeforeSpreadsheetExportEventArgs args)
    {
        args.Columns.Find(x => x.Field == nameof(FlowRun.ErrorMessage)).Width = "100px";

        //args.Columns.Add(new ExcelExportableColumn
        //{            
        //    Field = nameof(FlowRun.ErrorMessage),
        //    Title = "Error"
        //});
    }

    public class FlowRun
    {
        public string FileName { get; set; }
        public string Type { get; set; }
        public long? FileSize { get; set; }
        public string Source { get; set; }
        public FileProtocol SourceFileProtocol { get; set; }
        public string ErrorMessage { get; set; }
    }

    public enum FileProtocol
    {
        Unknown,
        PIX,
        CIX,
        SS
    }
}

.....
-->>Clicking on Button for changing grid mode and visibility of columns**
<TelerikToggleButton Title="Oznaceni vice radku" Icon="@FontIcon.ListUnordered" OnClick="@( _  =>{ CurrentStackItem.gSelectionMode=(CurrentStackItem.gSelectionMode==GridSelectionMode.Multiple)?GridSelectionMode.Single:GridSelectionMode.Multiple;CurrentStackItem.gSelectedItems = Enumerable.Empty<ExpandoObject>();})"
				Selected="@(CurrentStackItem.gSelectionMode==GridSelectionMode.Multiple)"></TelerikToggleButton>
....
<GridColumns>
-->>First "static" 2 columns**
<GridCheckboxColumn Visible=@(CurrentStackItem.gSelectionMode==GridSelectionMode.Multiple) @key="@("sIDX")" Width="70px" Locked="true" SelectAll="true" SelectAllMode="GridSelectAllMode.Current"></GridCheckboxColumn><GridColumn FieldType=@typeof(bool) Visible=@(IsPicker==true || (XSmall==false && CurrentStackItem.gSelectionMode==GridSelectionMode.Single )) @key="@("sCMD")" Filterable="false" Sortable="false" Locked="true" Width="@((IsPicker==true && XSmall==true)?"45px":"120px")">
			<HeaderTemplate>&nbsp;</HeaderTemplate><Template Context="ctx"><div @onclick:preventDefault="true" @onclick:stopPropagation="true">

-->> THIS part is hitting LOT OF TIME in debug (expected is at best only once)
				@{if (XSmall==false)
					{
-->> here is LOT OF dynamic buttons.

				}
					</div></Template></GridColumn>

-->> rest of the dynamic columns. In video, starting with "ciiislo org" in header

			@if (GridDef.ColStore != null && GridDef.ColStore.Any())
			{
				foreach (var it in GridDef.ColStore.Where(x => x.Verejny == true))
				{
					<GridColumn @key=@it.FldName Field=@it.FldName FieldType=@it.FldType Title=@it.VerejnyNazev ShowFilterCellButtons="false" Width=@it.cSirkaSestava
					TextAlign=@it.cZarovnani 
					><FooterTemplate>
							@if (it.Sumovat == true)
							{
								@context.Sum
							}
						</FooterTemplate></GridColumn>
				}
			}
		</GridColumns>

@* Use the Template to render the list of columns and add some custom styles *@ 

<TelerikGrid Data="@MyData"
             Pageable="true"
             PageSize="5"
             Width="700px"
             FilterMode="@GridFilterMode.FilterMenu"
             Sortable="true"
             ShowColumnMenu="true">
     <GridSettings>
     
     <GridColumnMenuSettings Sortable="true"
                             Lockable="false"
                             FilterMode="@ColumnMenuFilterMode.None" />
 </GridSettings>
    <GridColumns> 

 <GridCheckboxColumn Width="80px" HeaderClass="header-select-all" />   
        <GridColumn Field="@(nameof(SampleData.Id))" Width="80px" Title="Id" Id="id-column-id" />
        <GridColumn Field="@(nameof(SampleData.FirstName))" Title="First Name" Id="firstname-column-id" />
        <GridColumn Field="@(nameof(SampleData.LastName))" Title="Last Name" Id="lastname-column-id" />
        <GridColumn Field="@(nameof(SampleData.CompanyName))" Title="Company" Id="companyname-column-id" />
        <GridColumn Field="@(nameof(SampleData.Team))" Title="Team" Id="team-column-id" />
        <GridColumn Field="@(nameof(SampleData.HireDate))" Title="Hire Date" Id="hiredate-column-id" />
    </GridColumns>
</TelerikGrid>

@code {
    public string TextboxValue { get; set; } = string.Empty;

    public IEnumerable<SampleData> MyData = Enumerable.Range(1, 30).Select(x => new SampleData
    {
        Id = x,
        FirstName = $"FirstName {x}",
        LastName = $"LastName {x}",
        CompanyName = $"Company {x}",
        Team = "team " + x % 5,
        HireDate = DateTime.Now.AddDays(-x).Date
    });

    public class SampleData
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string CompanyName { get; set; }
        public string Team { get; set; }
        public DateTime HireDate { get; set; }
    }
}