谁能帮帮我(50分)

编写了一个断点续传的程序，但是每次都是将下载的文件保存在默认的源程序的目录下，请教如何实现将文件保存到指定目录下，我用了TIdFtp控件来实现ftp的文件下载，用了TidHttp控件实现http的文件下载，主要代码如下：
procedure Button2Click(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure IdHTTP1Work(Sender: TObject; AWorkMode: TWorkMode;
const AWorkCount: Integer);
procedure IdHTTP1WorkBegin(Sender: TObject; AWorkMode: TWorkMode;
const AWorkCountMax: Integer);
procedure IdHTTP1WorkEnd(Sender: TObject; AWorkMode: TWorkMode);
procedure IdHTTP1Status(ASender: TObject; const AStatus: TIdStatus;
const AStatusText: string);
procedure Button3Click(Sender: TObject);
procedure Button4Click(Sender: TObject);
private
AbortTransfer: Boolean; //是否中断
BytesToTransfer: LongWord; //下载总大小
procedure FtpDownLoad(aURL, aFile: string; bResume: Boolean);
procedure HttpDownLoad(aURL, aFile: string; bResume: Boolean);
procedure MyDownLoad(aURL, aFile: string; bResume: Boolean);
function GetProt(aURL: string): Byte;
function GetURLFileName(aURL: string): string;
procedure GetFTPParams(aURL: string; var sName, sPass, sHost, sPort,
sDir: string);
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

var
AverageSpeed: Double = 0;

implementation
uses mmsystem,unit2;
{$R *.dfm}

procedure TForm1.Button2Click(Sender: TObject);
begin
AbortTransfer := True;
end;

function TForm1.GetProt(aURL: string): Byte;
begin //检测下载的地址是http还是ftp
Result := 0;
if Pos('ftp', LowerCase(aURL)) = 1 then
Result := 1; //http协议
if Pos('http', LowerCase(aURL)) = 1 then
Result := 2; //ftp协议
end;

function TForm1.GetURLFileName(aURL: string): string;
var
i: integer;
s: string;
begin //返回下载地址的文件名
s := aURL;
i := Pos('/', s);
while i <> 0 do //去掉&quot;/&quot;前面的内容剩下的就是文件名了
begin
Delete(s, 1, i);
i := Pos('/', s);
end;
Result := s;
end;

procedure TForm1.GetFTPParams(aURL: string; var sName, sPass, sHost, sPort, sDir: string);
var
i, j: integer;
s, tmp: string;
begin //分析ftp地址的登陆用户名，密码和目录
s := aURL;
if Pos('ftp://', LowerCase(s)) <> 0 then //去掉ftp头
Delete(s, 1, 6);
i := Pos('@', s);
if i <> 0 then //地址含用户名，也可能含密码
begin
tmp := Copy(s, 1, i - 1);
s := copy(s, i+1, Length(s));
j := Pos(':', tmp);
if j <> 0 then //包含密码
begin
sName := Copy(tmp, 1, j - 1); //得到用户名
sPass := Copy(tmp, j + 1, i - j - 1); //得到密码
end else
begin
sName := tmp;
sPass := Inputbox('输入框','请输入登陆ftp密码','');
end;
end else //匿名用户
begin
sName := 'anonymous';
sPass := 'test@ftp.com';
end;
i := Pos(':', s);
j := Pos('/', s);
sHost := Copy(s, 1, j - 1); //主机
if i <> 0 then //含端口
sPort := Copy(s, i + 1, j - i - 1) else
sPort := '21'; //默认21端口

tmp := Copy(s, j + 1, Length(s));
while j <> 0 do
begin
Delete(s, 1, j);
j := Pos('/', s);
end; //目录
sDir := '/' + Copy(tmp, 1, Length(tmp) - Length(s) - 1);
end;

procedure TForm1.FtpDownLoad(aURL, aFile: string; bResume: Boolean);
var
tStream: TFileStream;
sName, sPass, sHost, sPort, sDir: string;
begin //ftp方式下载

if FileExists(aFile) then //建立文件流
tStream := TFileStream.Create(aFile, fmOpenWrite) else
tStream := TFileStream.Create(aFile, fmCreate);

GetFTPParams(aURL, sName, sPass, sHost, sPort, sDir);
with IdFTP1 do
try
if Connected then Disconnect; //重新连接
Username := sName;
Password := sPass;
Host := sHost;
Port := StrToInt(sPort);
Connect;
except
exit;
end;

IdFTP1.ChangeDir(sDir); //改变目录
BytesToTransfer := IdFTP1.Size(aFile);
try
if bResume then //续传
begin
tStream.Position := tStream.Size;
IdFTP1.Get(aFile, tStream, True);
end else
begin
IdFTP1.Get(aFile, tStream, False);
end;
finally
tStream.Free;
end;
end;

procedure TForm1.HttpDownLoad(aURL, aFile: string; bResume: Boolean);
var
tStream: TFileStream;
begin //Http方式下载

if FileExists(aFile) then //如果文件已经存在
tStream := TFileStream.Create(afile, fmOpenWrite) else
tStream := TFileStream.Create(aFile, fmCreate);

if bResume then //续传方式
begin
IdHTTP1.Request.ContentRangeStart := tStream.Size - 1;
tStream.Position := tStream.Size - 1; //移动到最后继续下载
IdHTTP1.Head(aURL);
IdHTTP1.Request.ContentRangeEnd := IdHTTP1.Response.ContentLength;
end else //覆盖或新建方式
begin
IdHTTP1.Request.ContentRangeStart := 0;
end;

try
IdHTTP1.Get(aURL, tStream); //开始下载
finally
tStream.Free;
end;
end;

procedure TForm1.MyDownLoad(aURL, aFile: string; bResume: Boolean);
begin
case GetProt(aURL) of
0: ShowMessage('不可识别的地址！');
2: HttpDownLoad(aURL, aFile, bResume);
1: FtpDownLoad(aURL, aFile, bResume);
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
aURL, aFile: string;
i:integer;
begin
aURL:= ComboBox1.Text;

//下载地址，例如&quot;http://www.2ccc.com/update/demo.exe&quot;

aFile:=GetURLFileName(aURL);



if FileExists(aFile) then
begin
case MessageDlg('文件已经存在，是否续传？', mtConfirmation, mbYesNoCancel, 0) of
mrYes: MyDownLoad(aURL, aFile, True); //续传
mrNo: MyDownLoad(aURL, aFile, False); //覆盖
mrCancel: Exit; //取消
end;

aFile:=savedialog1.FileName;

end
else
begin
MyDownLoad(aURL, aFile, False); //建立新文件下载

end;
end;

procedure TForm1.IdHTTP1Work(Sender: TObject; AWorkMode: TWorkMode;
const AWorkCount: Integer);
begin
if AbortTransfer then
begin //中断下载
IdHTTP1.Disconnect;
IdFTP1.Abort;
end;
ProgressBar1.Position := AWorkCount;
Application.ProcessMessages;
end;

procedure TForm1.IdHTTP1WorkBegin(Sender: TObject; AWorkMode: TWorkMode;
const AWorkCountMax: Integer);
begin
AbortTransfer := False;
if AWorkCountMax > 0 then
ProgressBar1.Max := AWorkCountMax else
ProgressBar1.Max := BytesToTransfer;
end;

procedure TForm1.IdHTTP1WorkEnd(Sender: TObject; AWorkMode: TWorkMode);
begin
playsound('download-complete.wav',0, snd_async);
showmessage('文件下载完毕');
ProgressBar1.Position := 0;
end;

procedure TForm1.IdHTTP1Status(ASender: TObject; const AStatus: TIdStatus;
const AStatusText: string);
begin
ListBox1.ItemIndex := ListBox1.Items.Add(AStatusText);
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
Close;
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
Form2.Show;

end;

end.
谢谢了