procedure ExportToXLSX(AStream: TStream);

uses
  dxDashboard.Control, // Declares the TdxDashboardControl component
  dxShellDialogs; // Declares the TdxSaveFileDialog component
// ...

procedure TMyForm.cxButtonExportToXLSXClick(Sender: TObject);
var
  AStream: TMemoryStream;
begin
  if not dxSaveFileDialog1.Execute(Handle) then Exit; // Displays the "Save File" dialog
  AStream := TMemoryStream.Create; // Creates a stream as an intermediary container
  try
    dxDashboardControl1.ExportToXLSX(AStream); // Exports content to a stream in the XLSX format
    AStream.SaveToFile(dxSaveFileDialog1.FileName); // Saves XLSX stream content to a file
  finally
    AStream.Free; // Releases the intermediary memory stream
  end;
end;

#include "dxDashboard.Control.hpp" // Declares the TdxDashboardControl component
#include "dxShellDialogs.hpp" // Declares the TdxSaveFileDialog component

// Add the following linker directives to the corresponding CPP source file:
#pragma link "dxDashboard.Control" // Required to use dxDashboard.Control.hpp declarations
#pragma link "dxShellDialogs" // Required to use dxShellDialogs.hpp declarations
// ...

void __fastcall TMyForm::cxButtonExportToXLSXClick(TObject *Sender)
{
  if(!dxSaveFileDialog1->Execute(Handle)) { return; } // Displays the "Save File" dialog
  TMemoryStream *AStream = new TMemoryStream(); // Creates a stream as an intermediary container
  try
  {
    dxDashboardControl1->ExportToXLSX(Handle); // Exports content to a stream in the XLSX format
    AStream->SaveToFile(dxSaveFileDialog1->FileName); // Saves XLSX stream content to a file
  }
  __finally
  {
    delete AStream; // Releases the intermediary memory stream
  }
}