使用Delphi XE将通过WinHTTP下载的文件保存到磁盘

发布时间：2020-12-15 10:11:50 所属栏目：大数据来源：网络整理

导读：对 this question的回答表明,在delphi中通过类型库导入使用WinHTTP是多么容易. 我为WinHTTP导入了类型库,然后尝试使用该API编写文件下载帮助程序函数.这是我有多远：我似乎无法弄清楚如何将IWinHttpRequest.ResponseStream(在TLB文件中声明为OleVariant)作

对 this question的回答表明,在delphi中通过类型库导入使用WinHTTP是多么容易.

我为WinHTTP导入了类型库,然后尝试使用该API编写文件下载帮助程序函数.这是我有多远：

我似乎无法弄清楚如何将IWinHttpRequest.ResponseStream(在TLB文件中声明为OleVariant)作为Stream保存到磁盘.

// IWinHttpRequest is defined by importing type library of WinHTTP.
// Microsoft WinHTTP Services,version 5.1 (Version 5.1) C:Windowssystem32winhttp.dll
function Download(const url,filename: String): Boolean;
var
   http: IWinHttpRequest;
   wUrl: WideString;
   fs:TFileStream;
   FileStream:IStream;
   sz,rd,wr:Int64;
begin
  try
   wUrl := url;
   http := CoWinHttpRequest.Create;
   http.open('GET',wurl,False);
   http.send(EmptyParam);

   FStatus := http.status; // 200=OK!
   result := FStatus=200;


   if result then
   begin
     fs := TFileStream.Create(filename,fmCreate,fmShareExclusive );
     try
      FileStream := TStreamAdapter.Create(fs,soReference) as IStream;
      sz := http.ResponseStream.Size;
      http.ResponseStream.CopyTo(FileStream,sz,wr);
     finally
         FileStream :=  nil;
         fs.Free;
     end;
   end;
  except
      result := false;
      // do not raise exceptions.
  end;
end;

摘自WinHTTP_TLB.pas：

IWinHttpRequest = interface(IDispatch)
    ['{016FE2EC-B2C8-45F8-B23B-39E53A75396B}']
    ......
    property ResponseStream: OleVariant read Get_ResponseStream;

更新：我现在在调用http.ResponseStream.CopyTo(…)时获得关于ole变体的运行时异常

EOleError 'Variant does not reference an automation object'.

解决方法

Warren,您必须使用 AxCtrls.TOleStream类来与 Classes.TFileStream通信响应流

这样的事情

IWinHttpRequest.ResponseStream -> TOleStream -> TFileStream

检查此示例代码

{$APPTYPE CONSOLE}

uses
  Variants,ActiveX,Classes,AxCtrls,WinHttp_TLB,SysUtils;


function Download(const url,filename: String): Boolean;
var
   http: IWinHttpRequest;
   wUrl: WideString;
   fs:TFileStream;
   HttpStream :IStream;
   sz,wr:Int64;
   FStatus : Integer;
   OleStream: TOleStream;
begin
  try
   wUrl := url;
   http := CoWinHttpRequest.Create;
   http.open('GET',False);
   http.send(EmptyParam);

   FStatus := http.status; // 200=OK!
   result := FStatus=200;

   if result then
   begin
    HttpStream:=IUnknown(http.ResponseStream) as IStream;
    OleStream:= TOleStream.Create(HttpStream);
    try
      fs:= TFileStream.Create(FileName,fmCreate);
      try
        OleStream.Position:= 0;
        fs.CopyFrom(OleStream,OleStream.Size);
      finally
        fs.Free;
      end;
    finally
      OleStream.Free;
    end;
   end;

  except
      result := false;
      // do not raise exceptions.
  end;
end;


begin
  try
    Download('http://foo.html','C:Fooanyfile.foo');
  except
    on E: Exception do
      Writeln(E.ClassName,': ',E.Message);
  end;
end.

（编辑：李大同）

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