Delphi XE2 DataSnap - 通过TStream与进度条下载文件 [英] Delphi XE2 DataSnap - Download File via TStream With Progress Bar

问题描述

我写了一个DataSnap服务器方法，返回一个TStream对象来传输一个文件。客户端应用程序调用该方法并读取流精细。我的问题是方法调用需要一段时间才能在TStream对象可用于读取之前完成，但是在服务器端，我可以看到方法调用只需要一秒钟来创建要返回的对象。我希望流对象将立即返回，以便我可以读取流并显示进度条以进行下载进度。还有另一种方式可以做到这一点吗？

服务器方法非常简单：

 code> function TServerMethods.DespatchDocument（sCompanyID，sDocOurRef：string）：TStream; 
 var 
 sSourceFilePath：string; 
 strFileStream：TFileStream; 
 begin 
 sSourceFilePath：= GetDocumentPDFFilePath（sCompanyID，sDocOurRef）; 
 
 strFileStream：= TFileStream.Create（sSourceFilePath，fmOpenRead）; 
结果：= strFileStream; 
结束
  

解决方案

这是我做了一会儿。我使用XE，没有机会清理它。

//服务器端：

 函数TServerMethods1.DownloadFile大小：Int64）：TStream; 
 begin 
结果：= TFileStream.Create（'upload.fil'，fmOpenRead或fmShareDenyNone）; 
大小：= Result.Size; 
 
 Result.Position：= 0; 
结束
  

//客户端：

  procedure TfMain.DownloadFile（Sender：TObject）; 
 var 
 RetStream：TStream; 
缓冲区：PByte; 
 Mem：TMemoryStream; 
 BytesRead：Integer; 
 DocumentId：Int64; 
大小：Int64; 
 filename：WideString; 
 BufSize：Integer; 
 begin 
 BufSize：= 1024; 
 
 try 
 Mem：= TMemoryStream.Create; 
 GetMem（Buffer，BufSize）; 
 
 try 
 RetStream：= FDownloadDS.DownloadFile（Size）; 
 RetStream.Position：= 0; 
 
 if（Size<> 0）then 
 begin 
 filename：='download.fil'; 
 
重复
 BytesRead：= RetStream.Read（指针（​​缓冲区）^，BufSize）; 
 
 if（BytesRead> 0）then 
 begin 
 Mem.WriteBuffer（Pointer（Buffer）^，BytesRead）; 
结束
 
 lStatus.Caption：= IntToStr（Mem.Size）+'/'+ IntToStr（Size）; 
 Application.ProcessMessages; 
 
 until（BytesRead< BufSize）; 
 
 if（Size<> Mem.Size）then 
 begin 
 raise Exception.Create（'Error downloads file ...'）; 
结束
 end 
 else 
 begin 
 lStatus.Caption：=''; 
结束
 finally 
 FreeMem（Buffer，BufSize）; 
 FreeAndNIl（Mem）; 
结束
除了
在E：Exception do 
 begin 
 lErrorMessage.Caption：= PChar（E.ClassName +'：'+ E.Message）; 
结束
结束
结束
  

您可以调整BufSize，但您喜欢。得到流的大小，直到我这样做才遇到麻烦。我试过XE2，似乎没有同样的问题，但我正在上传。可能有更好的方法来检索流的大小。如果我很快得到答案，我会让你知道....

另一个注意事项 - 我还没有弄清楚如何在服务器上显示一个进度条侧。我还在试图弄清楚这一点。

我希望这有帮助！如果您有任何疑问，请告知我！

I've written a DataSnap server method that returns a TStream object to transfer a file. The client application calls the method and reads the stream fine. My issue is that the method call takes a while to complete before the TStream object is available to read, but on the server side I can see that the method call only takes a second to create the object to return. I was hoping the stream object would be returned immediately so that I can read the stream and display a progress bar for the download progress. Is there another way I can do this?

The server method is very simple :

function TServerMethods.DespatchDocument(sCompanyID, sDocOurRef: string): TStream;
var
  sSourceFilePath: string;
  strFileStream: TFileStream;
begin
  sSourceFilePath := GetDocumentPDFFilePath(sCompanyID, sDocOurRef);

  strFileStream := TFileStream.Create(sSourceFilePath, fmOpenRead);
  Result := strFileStream;
end;

解决方案

This is how I did it a while back. I used XE and haven't had a chance to clean it up.

//Server side:

function TServerMethods1.DownloadFile(out Size: Int64): TStream;
begin
    Result := TFileStream.Create('upload.fil', fmOpenRead or fmShareDenyNone);
    Size := Result.Size;

    Result.Position := 0;
end;

//Client side:

procedure TfMain.DownloadFile(Sender: TObject);
var
    RetStream: TStream;
    Buffer: PByte;
    Mem: TMemoryStream;
    BytesRead: Integer;
    DocumentId: Int64;
    Size: Int64;
    filename: WideString;
    BufSize: Integer;
begin
    BufSize := 1024;

    try
      Mem := TMemoryStream.Create;
      GetMem( Buffer, BufSize );

      try
        RetStream := FDownloadDS.DownloadFile(Size);
        RetStream.Position := 0;

        if ( Size <> 0 ) then
        begin
          filename := 'download.fil';

          repeat
            BytesRead := RetStream.Read( Pointer( Buffer )^, BufSize );

            if ( BytesRead > 0 ) then
            begin
              Mem.WriteBuffer( Pointer( Buffer )^, BytesRead );
            end;

            lStatus.Caption := IntToStr( Mem.Size ) + '/' + IntToStr( Size );
            Application.ProcessMessages;

          until ( BytesRead < BufSize );

          if ( Size <> Mem.Size ) then
          begin
            raise Exception.Create( 'Error downloading file...' );
          end;
        end
        else
        begin
          lStatus.Caption := '';
        end;
      finally
        FreeMem( Buffer, BufSize );
        FreeAndNIl(Mem);
      end;
    except
      on E: Exception do
      begin
        lErrorMessage.Caption := PChar( E.ClassName + ': ' + E.Message );
      end;
    end;
end;

You can adjust BufSize however you like. I was having trouble getting the size of the stream until I did it this way. I experimented with XE2 and didn't seem to have the same problem but I was uploading. There is probably a better way to retrieve the size of the stream. If I get the answer soon I'll let you know....

On another note - I haven't figured out how to display a progress bar on the server side. I'm still trying to figure this out too.

I hope this helps! Let me know if you have any questions!

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