Через CheckBox запрещаем изменять размер колонок в таблице DBGrid

Unit.cpp

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
	: TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::CheckBox1Click(TObject *Sender)
{
  if(CheckBox1->Checked)
	{
	DBGrid1->Options=TDBGridOptions(DBGrid1->Options)>>dgColumnResize;
	}
	else
	{
	DBGrid1->Options=TDBGridOptions(DBGrid1->Options)<<dgColumnResize;
	}

}

Unit.h

//---------------------------------------------------------------------------

#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <System.Classes.hpp>
#include <Vcl.Controls.hpp>
#include <Vcl.StdCtrls.hpp>
#include <Vcl.Forms.hpp>
#include <Data.DB.hpp>
#include <Data.Win.ADODB.hpp>
#include <Vcl.DBGrids.hpp>
#include <Vcl.Grids.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:	// IDE-managed Components
	TADOConnection *ADOConnection1;
	TADOTable *ADOTable1;
	TDBGrid *DBGrid1;
	TDataSource *DataSource1;
	TCheckBox *CheckBox1;
	void __fastcall CheckBox1Click(TObject *Sender);
private:	// User declarations
public:		// User declarations
	__fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif