关于多线程与可视控件编程的问题

Question

有一个窗体form1上的Panel4放着一个gif进度条图片，默认该Panel4.Visible:=false;现在要进行多线程数据查询，当点击查询按钮时，Panel4就会显示，然后执行数据查询，将结果显示在Dbgrideh上后让Panel4隐藏，然后将查询的结果数显示在SpeedButton1上，即可。以下是我的代码，有人说可视控件不能放在多线程中（我刚运行这个代码时可以正常查询出结果，效果与预期的相同，但连续查询了几次就会报错），我是刚学多线程的，对多线程只知皮毛，想请大侠帮助改一改下面的代码，谢谢了！！！function doloop:Longint;stdcall;//执行查询核心及进度条线程函数
begin
    form1.Panel4.Visible:=true;//让进度条面板显示
    with form1.OraSession1 do
    try
        ConnectString:='ddl/[email protected]:1521:gg';
        Options.Direct:=true;
        Connected:=true;
    except
        Free;
        showmessage('系统与服务器断开连接！请与管理员联系！');
        application.Terminate;
    end;
    with form1.OraQuery1 do
    try
        Close;
        SQL.Clear;
        SQL.Add(cx_samesql);
        Prepared;
        Open;
    except
        Free;
    end;
    form1.OraQuery1.Last;
    form1.SpeedButton1.Caption:='查询（共查出 '+inttostr(form1.OraQuery1.RecordCount)+'条记录）';
    form1.OraQuery1.First;
    form1.Panel4.Visible:=false;//让进度条面板隐藏
    result:=0;
end;procedure Tform1.BitBtn1Click(Sender: TObject);//点击开始查询
begin
    hloopHandle:=CreateThread(nil,0,@doloop,nil,0,dloopThreadID);
    if hloopHandle=0 then MessageBox(Handle,'No Thread',nil,MB_OK);
    DBGridEh1.DataSource:=OraDataSource1;
end;

Answer 1

线程中对VCL 控件操作 要用 TThread的Synchronize方法，Synchronize把访问VCL控件函数放到主线程中去执行 

Answer 2

{ Important: Methods and properties of objects in VCL or CLX can only be used
  in a method called using Synchronize, for example,      Synchronize(UpdateCaption);  and UpdateCaption could look like,    procedure aaaa.UpdateCaption;
    begin
      Form1.Caption := 'Updated in a thread';
    end; }

Answer 3

哪位大侠可以写一个多线程控制VCL可视控件的简要例子吗？

Answer 4

现在改成这样，但还是报错，头痛啊！~
1、线程unit：
unit cx;
interface
uses
  Classes;
type
  Tcxtheard = class(TThread)
  private
    { Private declarations }
    procedure UpdateCaption;
    procedure UpdateCaption2;
  protected
    procedure Execute; override;
  end;
implementation
uses main;
procedure Tcxtheard.UpdateCaption;
begin
    Form1.Panel1.Visible:=true;
end;
procedure Tcxtheard.UpdateCaption2;
begin
    Form1.Panel1.Visible:=false;
end;
procedure Tcxtheard.Execute;
begin
    Synchronize(UpdateCaption);
    with form1.OraQuery1 do
    try
        Close;
        SQL.Clear;
        SQL.Add('select * from table1');
        Prepared;
        Open;
    except
        Free;
    end;
    Synchronize(UpdateCaption2);
end;
end.2、主窗体代码：
unit main;
interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Buttons, DB, DBAccess, Ora, MemDS, GifImage,
  ExtCtrls, Grids, DBGrids, GridsEh, DBGridEh;
type
  TForm1 = class(TForm)
    OraSession1: TOraSession;
    OraQuery1: TOraQuery;
    OraDataSource1: TOraDataSource;
    SpeedButton1: TSpeedButton;
    GroupBox1: TGroupBox;
    Label1: TLabel;
    Edit1: TEdit;
    Button1: TButton;
    DBGridEh1: TDBGridEh;
    Panel1: TPanel;
    Image1: TImage;
    procedure FormShow(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
uses cx;
{$R *.dfm}
procedure TForm1.FormShow(Sender: TObject);
var
    i:integer;
begin
    image1.Picture.LoadFromFile(ExtractFilePath(paramstr(0))+'load.gif');//导入进度条图像
    with OraSession1 do
    try
        ConnectString:='ddl/[email protected]:1521:gg';
        Options.Direct:=true;
        Connected:=true;
    except
        Free;
        showmessage('系统与服务器断开连接！请与管理员联系！');
        application.Terminate;
    end;
    for i:=0 to DBGridEh1.FieldCount-1 do
    begin
        DBGridEh1.Columns[i].Width:=89;
    end;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
    Thread1:Tcxtheard;
begin
    Thread1:=Tcxtheard.Create(false);
    Thread1.FreeOnTerminate:=true;
end;
end.