Urldownloadtofile progress prompt

Urlmon. dll has an API for download. The definition in msdn is as follows:

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

Delphi's urlmon. PAS has its Pascal statement:

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

Szurl is the URL of the file to be downloaded, szfilename is another file name, dwreserved is the reserved parameter, and 0 is passed. If you do not need a progress prompt, it is easy to call this function. For example, to download the song "http: // 218.95.47.htm/page/jxzy/xszb/web/fourteens/music/qilique" and save it as "D: \ music \ qilixiang", you can call it like this:

Urldownloadtofile (nil, 'HTTP: // 218.95.47.htm/page/jxzy/xszb/web/fourteens/music/qiliqing', 'd: \ music \ qilixiangjie ', 0, nil );

However, the disadvantage is that there is no progress prompt and the call thread will be blocked. The last parameter lpfncb is required to obtain the progress prompt. It is an interface type ibindstatuscallback, which is defined as follows:

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;

The progress prompt depends on the onprogress method of this interface. We can define a class that implements the ibindstatuscallback interface. Only the onprogress method can be processed. if you do nothing about other methods, s_ OK is returned. Here is a brief description of onprogress:

Ulprogress: current progress Value
Ulprogressmax: total progress
Ulstatuscode: status value, which is the tagbindstatus enumeration. It indicates you are looking for resources, and you are connecting to these statuses. For details, refer to msdn. We do not need to care about it here.
Szstatustext: Status string, and we don't care about it either.

So if we use percentage to indicate the progress, it is floattostr (ulprogress * 100/ulprogressmax) + '/%', which is simple. To cancel the task before the download is complete, you can return e_abort in onprogress.
I encapsulated urldownloadtofile and its progress prompt function into a Thread class. The source code of this class is as follows:

 

{ 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.

Use deleteurlcacheentry to clear the cache and then use urldownloadtofile to download the file.

/*************************************** *****************/
Cstring szurl = "http://www.dtapp.cn ";

Deleteurlcacheentry (szurl); // clear the cache
Cstring szfilename = "C :\\ dtapp.txt ";

If (s_ OK = urldownloadtofile (null, szurl, szfilename, null, null ))
{
// Download successful
}
Else
{
// Download failed
}