從網絡上下載文件的兩種方法

 

兩種方法使用的Com函數都來源於UrlMon，記得先引用。

 

一、URLDownloadToFile

直接下載文件到磁盤，URLDownloadToFile聲明如下：

function URLDownloadToFile(
    Caller: IUnknown; 
    URL: PWideChar;           { 下載的路徑 }
    FileName: PWideChar;   { 保存到的路徑 }
    Reserved: DWORD;
    StatusCB: IBindStatusCallback
): HResult; stdcall;

function URLDownloadToFileA(Caller: IUnknown; URL: PAnsiChar; FileName: PAnsiChar; Reserved: DWORD; StatusCB: IBindStatusCallback): HResult; stdcall;
function URLDownloadToFileW(Caller: IUnknown; URL: PWideChar; FileName: PWideChar; Reserved: DWORD; StatusCB: IBindStatusCallback): HResult; stdcall;

調用示例：
if UrlDownloadToFile(nil, 'http://www.xxxx.com/xxx.xx', 'c:/1.xx', 0, nil) = 0 then 
  MessageBox(handle, '下載成功', '', 0)

else

  MessageBox(handle, '下載失敗', '', 0);

 

URLDownloadToFile下載文件前先在本地的緩存中查找文件，如果緩存有則不會再去網上抓最新的文件，希望總是獲取新文件時可在URL后加一個隨機數，或用DeleteUrlCacheEntry(URL)清理緩存后再下載

 

二、URLOpenStream 

下載到 IStream 流，聲明為：

function URLOpenStream(
    p1: IUnknown;

    p2: PWideChar;              { 下載的路徑 }

    p3: DWORD;

    p4: IBindStatusCallback { 接口, 下載后的通過它取得數據 }

): HResult; stdcall;

function URLOpenStreamA(p1: IUnknown; p2: PAnsiChar; p3: DWORD; p4: IBindStatusCallback): HResult; stdcall;

function URLOpenStreamW(p1: IUnknown; p2: PWideChar; p3: DWORD; p4: IBindStatusCallback): HResult; stdcall;

 

IBindStatusCallback 接口的實現

  TBindStatusCallback = class(TInterfaceList, IBindStatusCallback)
  public
    function OnStartBinding(dwReserved: DWORD; pib: IBinding): HResult; stdcall;
    function GetPriority(out nPriority): HResult; stdcall;
    function OnLowResource(reserved: DWORD): HResult; stdcall;
    function OnProgress(ulProgress, ulProgressMax, ulStatusCode: ULONG;
      szStatusText: LPCWSTR): HResult; stdcall;
    function OnStopBinding(hresult: HResult; szError: LPCWSTR): HResult; stdcall;
    function GetBindInfo(out grfBINDF: DWORD; var bindinfo: TBindInfo): HResult; stdcall;
    function OnDataAvailable(grfBSCF: DWORD; dwSize: DWORD; formatetc: PFormatEtc;
      stgmed: PStgMedium): HResult; stdcall;
    function OnObjectAvailable(const iid: TGUID; punk: IUnknown): HResult; stdcall; 

end; 

{ TBindStatusCallback }

function TBindStatusCallback.GetBindInfo(out grfBINDF: DWORD;
  var bindinfo: TBindInfo): HResult;
begin
  Result := S_OK;
end;

function TBindStatusCallback.GetPriority(out nPriority): HResult;
begin
  Result := S_OK;
end;

function TBindStatusCallback.OnDataAvailable(grfBSCF, dwSize: DWORD;
  formatetc: PFormatEtc; stgmed: PStgMedium): HResult;
var
  Stream: IStream;
  MS: TMemoryStream;
begin
  if dwSize > 0then
  begin
    Stream := IStream(stgmed.stm);
    MS := TMemoryStream.Create;
    MS.SetSize(dwSize);
    Stream.Read(MS.Memory, dwSize, nil);
    //從MS取數據...
    MS.Free;
    Result := S_OK;
  end else Result := E_ABORT;
end;

function TBindStatusCallback.OnLowResource(reserved: DWORD): HResult;
begin
  Result := S_OK;
end;

function TBindStatusCallback.OnObjectAvailable(const iid: TGUID;
  punk: IInterface): HResult;
begin
  Result := S_OK;
end;

function TBindStatusCallback.OnProgress(ulProgress, ulProgressMax,
  ulStatusCode: ULONG; szStatusText: LPCWSTR): HResult;
begin
  //可實現偵測進度，實現代碼在此寫
  Result := S_OK;
end;

function TBindStatusCallback.OnStartBinding(dwReserved: DWORD;
  pib: IBinding): HResult;
begin
  Result := S_OK;
end;

function TBindStatusCallback.OnStopBinding(hresult: HResult;
  szError: LPCWSTR): HResult;
begin
  Result := S_OK;
end;
 

調用代碼：
 var
  url: string;
  MyBindStatusCallback: IBindStatusCallback;

begin
  MyBindStatusCallback := TBindStatusCallback.Create;
  if Succeeded(URLOpenStream(nil, 'http://www.xxxx.com/xxx.xx', 0, MyBindStatusCallback)) then
    //下載成功!
  else
    //下載失敗!;
end;

http://blog.csdn.net/nhconch/article/details/5470777