===============服务端================
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, IdBaseComponent, IdComponent, IdUDPBase, IdUDPServer,idsockethandle,
  Gauges;

type
  TForm1 = class(TForm)
    IdUDPServer1: TIdUDPServer;
    SaveDialog1: TSaveDialog;
    Gauge1: TGauge;
    procedure IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
      ABinding: TIdSocketHandle);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    FileName:string;//保存收到的文件名
    FileSize:integer;//文件的找度
    mem:tFileStream;
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
  ABinding: TIdSocketHandle);
var
  str:string;
begin
  aData.Seek(0,0);
  setLength(str,aData.size);
  aData.Read(str[1],aData.Size);
  if pos('Send File:File name:',str)>0 then begin
    delete(str,1,length('Send File:File name:'));
    fileName:=str;
    //showmessage(str);
    str:='Received File ok';
    abinding.SendTo(aBinding.PeerIP,aBindIng.PeerPort,str[1],length(str));
   // idUDPserver1.Send(idUDPServer1.);
  end else if pos('File Length:',str)>0 then begin
    delete(str,1,length('File Length:'));
    FileSize:=strToIntDef(str,0);
    SaveDialog1.FileName:=fileName;
    if saveDialog1.Execute then begin
      FileName:=saveDialog1.FileName;
      if FileExists(filename) then
         deleteFile(filename);
      if mem<>nil then begin
        mem.Free;
        mem:=nil;
      end;
      if not fileExists(FileName) then
        mem:=TFileStream.Create(FileName,sysutils.fmOpenReadWrite or fmCreate)
      else
        mem:=TFileStream.Create(FileName,fmopenReadWrite);
      str:='get file Length ok';
      aBinding.SendTo(aBinding.PeerIP,aBinding.PeerPort,str[1],length(str));
    end else begin    //saveDialog1.execute
      str:='received File cancel';
      aBinding.SendTo(aBinding.PeerIP,aBinding.PeerPort,str[1],length(str));
    end;
  end else if pos('File Send End',str)>0 then begin
    if mem<>nil then begin
      mem.Free;
      mem:=nil;
      str:='Received File Successed';
      aBinding.SendTo(aBinding.PeerIP,aBinding.PeerPort,str[1],length(str));
      filename:='';
      fileSize:=0;
    end;
  end else begin
    if mem<>nil then begin
      mem.Seek(0,2);
      aData.Seek(0,0);
      mem.CopyFrom(aData,aData.Size);
      gauge1.Progress:=round(mem.size/fileSize*100);
      str:='received ok';
      abinding.SendTo(aBinding.PeerIP,aBinding.PeerPort,str[1],length(str));
      application.ProcessMessages;
    end;

  end;

end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  if mem<>nil then
    mem.Free;
end;

end.

=====================================



===============客户端================
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Gauges, IdBaseComponent, IdComponent, IdUDPBase,
  IdUDPClient;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    IdUDPClient1: TIdUDPClient;
    Gauge1: TGauge;
    Button1: TButton;
    OpenDialog1: TOpenDialog;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  receivedString:string;
  mem:tfileStream;
  posi,len:integer;
  p:array [0..1023] of byte;
begin
  if opendialog1.Execute then begin
    idUDPClient1.Host:=edit1.Text;
    idUDPClient1.Active:=true;

    idUDPClient1.Send('Send File:File name:'+opendialog1.FileName);
    ReceivedString:=idUDPClient1.ReceiveString;
    if uppercase(Receivedstring)=upperCase('Received File ok') then
    begin
      //showmessage('服务器提示收到文件名');
      mem:=tfileStream.Create(opendialog1.FileName,fmOpenRead);
      try
        posi:=0;
        idUDPclient1.Send('File Length:'+IntToStr(mem.Size));
        receivedString:=idUDPClient1.ReceiveString();
        if uppercase(receivedString)=upperCase('get file Length ok') then begin
           while posi<mem.Size  do begin
             len:=1024;             //只能发 1024
             if mem.Size<1024 then  //如果长度不到 1024
               len:=mem.Size;
             mem.Read(p,len);
             idUDPClient1.SendBuffer(p,len);
             inc(posi,len);
             gauge1.Progress:=round(posi/mem.size*100);
             receivedString:=idUDPClient1.ReceiveString();
             if upperCase(ReceivedString)<>upperCase('received ok') then
               break;
             application.ProcessMessages;
           end;    //end while
           idUDPClient1.Send('File Send End');
           if idUdpClient1.ReceiveString()='Received File Successed' then
             showmessage('文件成功发送');
         end else showmessage('cancel');// end while
       //end 取得文件长度
      finally
        mem.Free;
      end;
    end;
  end;//opendialog1.execute
end;

end.
=====================================