求教，代码执行到adoquery1.execsql的时候报错，请教原因

Question

求教，代码执行到adoquery1.execsql的时候报错missing connection or connectionstring
谢谢各位
求教原因procedure TForm1.BitBtn1Click(Sender: TObject);var
access:string;
const
link_str='Provider=%s; Data Source=%s';
dataprovider='microsoft.jet.oledb.4.0';
begin
open_database.FileName:='*.mdb';
if open_database.Execute then
begin
    access:=open_database.FileName;
    edit1.Text:=access;
    adoconnection1.Connected:=false;
    adoconnection1.ConnectionString:=format(link_str,[dataprovider,access]);
    adoconnection1.Connected:=true;
    adoconnection1.GetTableNames(listbox1.Items);end;end;procedure TForm1.BitBtn2Click(Sender: TObject);
var
tablename:string;
begin
dbgrid1.DataSource:=datasource1;
datasource1.DataSet:=adoquery1;
tablename:=listbox1.Items.Strings[listbox1.itemIndex];adoquery1.Close;
adoquery1.SQL.Clear;
adoquery1.SQL.Text:='select * from '+tablename+'';
try
  adoquery1.ExecSQL;
except
 showmessage('error');
 end;

Answer 1

用open也是一样的，出一样的错误

Answer 2

adoconnection1.Connected:=true;
ADOQuery1.Connection := ADOConnection1;

Answer 3

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, DB, ADODB, Grids, DBGrids;type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    ADOConnection1: TADOConnection;
    open_database: TOpenDialog;
    ListBox1: TListBox;
    ADOQuery1: TADOQuery;
    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
var
  access:string;
const
  link_str='Provider=%s; Data Source=%s';
  dataprovider='microsoft.jet.oledb.4.0';
begin
  open_database.FileName:='*.mdb';
  if open_database.Execute then
  begin
    access:=open_database.FileName;
    edit1.Text:=access;
    adoconnection1.Connected:=false;
    adoconnection1.ConnectionString:=format(link_str,[dataprovider,access]);
    adoconnection1.Connected:=true;
    adoconnection1.GetTableNames(listbox1.Items);
  end;
end;procedure TForm1.Button2Click(Sender: TObject);
var
  tablename:string;
begin
  dbgrid1.DataSource:=datasource1;
  datasource1.DataSet:=adoquery1;
  //tablename:=listbox1.Items.Strings[listbox1.itemIndex];
  tablename:=ListBox1.Items.Strings[0];
  adoquery1.Close;
  adoquery1.SQL.Clear;
  adoquery1.SQL.Text:='select * from '+tablename+'';
  try
    //adoquery1.ExecSQL;
    ADOQuery1.Open;
  except
   showmessage('error');
  end;
end;
end.

Answer 4

问题已经解决，忘记设置adoconnection了，谢谢各位