function TImageFileList.GetIndex: integer;
begin
  result:=FIndex;
end;

--------------------------------------------------------------------------------

function TImageFileList.GetNextFileName: string;
begin
  if Findex=FStrListFile.Count-1 then
    Findex:=0
  else
    inc(Findex);

  result:=FStrListFile.Strings[Findex];
end;

--------------------------------------------------------------------------------

function TImageFileList.GetPreFileName: string;
begin
  if Findex=0 then
    Findex:=FStrListFile.Count-1
  else
    dec(Findex);

  result:=FStrListFile.Strings[Findex];
end;

--------------------------------------------------------------------------------

procedure TImageFileList.SetIndex(AIndex: integer);
begin
  FIndex:=AIndex;
end;

  3. 过程JpgToBmp及函数IsJpgFile的代码如下所示：

//转换jpg到bmp                 

 procedure JpgToBmp(const JpgFileName:string;AJpg:TJpegImage;Abmp:Tbitmap);
begin
  try
    AJpg.LoadFromFile(JpgFileName);
    Abmp.Assign(AJpg);
  finally
  end;
end;

//仅从扩展名上来判断是否是jpg格式的文件
function  IsJpgFile(const FileName:string):boolean;
begin
  result:=(LowerCase( ExtractFileExt(FileName))=''.jpg'') or (LowerCase( ExtractFileExt(FileName))=''.jpeg'');
end;

4.  我们在窗体的OnCreate和OnDestroy事件处理句柄里添加如下代码：

procedure TForm1.FormCreate(Sender: TObject);
begin
  //设置图标间距，也即缩略图间距
  ListView_SetIconSpacing(listview1.handle,90,120);

  OriginalBmp:=Tbitmap.Create;
  ThumbJpg:=TJpegImage.Create;

  PreViewBmp:=Tbitmap.Create;
  PreViewJpg:=TJpegImage.Create;

  ThumbBmp:=TBitmap.Create;
  //缩略图的边框为：80*80，显示图片大小为：64*64
  ThumbBmp.Height:=80;
  ThumbBmp.Width:=80;
  ThumbBmp.PixelFormat:=pf24bit;
  imagelist1.Height:=80;
  imagelist1.Width:=80;
  listview1.LargeImages:=imagelist1;
  listview1.ViewStyle:=vsicon;

  ImageFileList:=TImageFileList.Create;
  ImageFileList.Clear;

  ProgressBar1:=TProgressBar.Create(self);
  ProgressBar1.Parent:=StatusBar1;
  ProgressBar1.Visible:=false;
  ProgressBar1.Width:=200;
  ProgressBar1.Height:=StatusBar1.Height-4;
  ProgressBar1.Left:=StatusBar1.Width-ProgressBar1.Width;
  ProgressBar1.Top:=2;

  IsRefreshImageFinished:=true;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  OriginalBmp.Free;
  ThumbBmp.Free;
  ImageFileList.Free;
  ThumbJpg.Free;
  PreViewBmp.Free;
  PreViewJpg.Free;
  ProgressBar1.Free;
end;

5. 在ShellTreeView1的OnChange事件里添加下面代码：

procedure TForm1.ShellTreeView1Change(Sender: TObject; Node: TTreeNode);
var
  dir:string;
begin
  //如果上次的RefreshImage过程还没有结束，就退