UrlDownloadToFile的进度提示

来源:互联网 时间:1970-01-01

urlmon.dll中有一个用于下载的API,MSDN中的定义如下:

HRESULT URLDownloadToFile( LPUNKNOWN pCaller, LPCTSTR szURL, LPCTSTR szFileName, DWORD dwReserved, LPBINDSTATUSCALLBACK lpfnCB);

Delphi的UrlMon.pas中有它的Pascal声明:

function URLDownloadToFile( pCaller: IUnKnown, szURL: PAnsiChar, szFileName: PAnsiChar, dwReserved: DWORD, lpfnCB: IBindStatusCallBack;);HRESULT;stdcall;

szURL是要下载的文件的URL地址,szFileName是另存文件名,dwReserved是保留参数,传递0。如果不需要进度提示的话,调用这个函数很简单。比如要下载http://218.95.47.224/page/jxzy/XSZB/web/fourteens/Music/qili.mp3 这首歌,并保存为D:/ Music/七里香.mp3,就可以这样调用:

    URLDownloadToFile(nil,'http://218.95.47.224/page/jxzy/XSZB/web/fourteens/Music/qili.mp3 ','D:/ Music/七里香.mp3',0,nil);

不过这样做的缺点是没有进度提示,而且会阻塞调用线程。如果要获得进度提示就要用到最后一个参数lpfnCB了,它是一个接口类型IBindStatusCallBack,定义如下:

IBindStatusCallback = interface ['{79eac9c1-baf9-11ce-8c82-00aa004ba90b}'] 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;

进度提示就靠这个接口的OnProgress方法了。我们可以定义一个实现 IBindStatusCallback 接口的类,只处理一下OnProgress方法就可以了,其它方法咱啥都不做,就返回S_OK。下面简要说一下OnProgress:

ulProgress :当前进度值
ulProgressMax :总进度
ulStatusCode: 状态值,是tagBINDSTATUS枚举。表明正在寻找资源啊,正在连接啊这些状态。具体请查看MSDN,我们这里不需要关心它
szStatusText:状态字符串,咱也不关心它

所以我们用百分比来表示进度的话就是FloatToStr(ulProgress*100/ulProgressMax)+'/%',简单吧。如果要在下载完成前取消任务,可以在OnProgress中返回E_ABORT。
我把UrlDownloadToFile及其进度提示功能都封装进了一个线程类中,这个类的源码如下: 

 

{ Delphi File Download Thread Class , Copyright (c) Zhou Zuoji }unit FileDownLoadThread;interfaceuses
Classes, SysUtils, Windows, ActiveX, UrlMon;const S_ABORT = HRESULT($80004004); type TFileDownLoadThread = class; TDownLoadProcessEvent = procedure(Sender:TFileDownLoadThread;Progress, ProgressMax:Cardinal) of object; TDownLoadCompleteEvent = procedure(Sender:TFileDownLoadThread) of object ; TDownLoadFailEvent = procedure(Sender:TFileDownLoadThread;Reason:LongInt) of object ; TDownLoadMonitor = class( TInterfacedObject, IBindStatusCallback ) private FShouldAbort: Boolean; FThread:TFileDownLoadThread; protected 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; public constructor Create(AThread:TFileDownLoadThread); property ShouldAbort: Boolean read FShouldAbort write FShouldAbort; end; TFileDownLoadThread = class( TThread ) private FSourceURL: string; FSaveFileName: string; FProgress,FProgressMax:Cardinal; FOnProcess: TDownLoadProcessEvent; FOnComplete: TDownLoadCompleteEvent; FOnFail: TDownLoadFailEvent; FMonitor: TDownLoadMonitor; protected procedure Execute; override; procedure UpdateProgress(Progress, ProgressMax, StatusCode: Cardinal; StatusText:string); procedure DoUpdateUI; public constructor Create( ASrcURL, ASaveFileName: string; AProgressEvent:TDownLoadProcessEvent = nil; ACompleteEvent:TDownLoadCompleteEvent = nil;AFailEvent:TDownLoadFailEvent=nil;CreateSuspended: Boolean=False ); property SourceURL: string read FSourceURL; property SaveFileName: string read FSaveFileName; property OnProcess: TDownLoadProcessEvent read FOnProcess write FOnProcess; property OnComplete: TDownLoadCompleteEvent read FOnComplete write FOnComplete; property OnFail: TDownLoadFailEvent read FOnFail write FOnFail; end;implementationconstructor TDownLoadMonitor.Create(AThread: TFileDownLoadThread);begin inherited Create; FThread:=AThread; FShouldAbort:=False;end;function TDownLoadMonitor.GetBindInfo( out grfBINDF: DWORD; var bindinfo: TBindInfo ): HResult;begin result := S_OK;end;function TDownLoadMonitor.GetPriority( out nPriority ): HResult;begin Result := S_OK;end;function TDownLoadMonitor.OnDataAvailable( grfBSCF, dwSize: DWORD; formatetc: PFormatEtc; stgmed: PStgMedium ): HResult;begin Result := S_OK;end;function TDownLoadMonitor.OnLowResource( reserved: DWORD ): HResult;begin Result := S_OK;end;function TDownLoadMonitor.OnObjectAvailable( const iid: TGUID; punk: IInterface ): HResult;begin Result := S_OK;end;function TDownLoadMonitor.OnProgress( ulProgress, ulProgressMax, ulStatusCode: ULONG; szStatusText: LPCWSTR ): HResult;begin if FThread<>nil then FThread.UpdateProgress(ulProgress,ulProgressMax,ulStatusCode,''); if FShouldAbort then Result := E_ABORT else Result := S_OK;end;function TDownLoadMonitor.OnStartBinding( dwReserved: DWORD; pib: IBinding ): HResult;begin Result := S_OK;end;function TDownLoadMonitor.OnStopBinding( hresult: HResult; szError: LPCWSTR ): HResult;begin Result := S_OK;end;{ TFileDownLoadThread }constructor TFileDownLoadThread.Create( ASrcURL, ASaveFileName: string;AProgressEvent:TDownLoadProcessEvent ; ACompleteEvent:TDownLoadCompleteEvent;AFailEvent:TDownLoadFailEvent; CreateSuspended: Boolean );begin if (@AProgressEvent=nil) or (@ACompleteEvent=nil) or (@AFailEvent=nil) then CreateSuspended:=True; inherited Create( CreateSuspended ); FSourceURL:=ASrcURL; FSaveFileName:=ASaveFileName; FOnProcess:=AProgressEvent; FOnComplete:=ACompleteEvent; FOnFail:=AFailEvent;end;procedure TFileDownLoadThread.DoUpdateUI;begin if Assigned(FOnProcess) then FOnProcess(Self,FProgress,FProgressMax);end;procedure TFileDownLoadThread.Execute;var DownRet:HRESULT;begin inherited; FMonitor:=TDownLoadMonitor.Create(Self); DownRet:= URLDownloadToFile( nil, PAnsiChar( FSourceURL ), PAnsiChar( FSaveFileName ), 0,FMonitor as IBindStatusCallback); if DownRet=S_OK then begin if Assigned(FOnComplete) then FOnComplete(Self); end else begin if Assigned(FOnFail) then FOnFail(Self,DownRet); end; FMonitor:=nil;end;procedure TFileDownLoadThread.UpdateProgress(Progress, ProgressMax, StatusCode: Cardinal; StatusText: string);begin FProgress:=Progress; FProgressMax:=ProgressMax; Synchronize(DoUpdateUI); if Terminated then FMonitor.ShouldAbort:=True;end;end.


使用DeleteUrlCacheEntry清理缓存后再使用URLDownloadToFile下载文件。

/********************************************************/
CString szUrl = "http://www.dtapp.cn";

DeleteUrlCacheEntry (szUrl); // 清理缓存
CString szFileName = "C://dtapp.txt";

 if (S_OK == URLDownloadToFile(NULL, szUrl, szFileName, NULL,NULL)) 
 {
  // 下载成功
 }
 else
 {
  // 下载失败
 }



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