Delphi知识中心
www.delphi.ee
提供Delphi技术知识
与Delphi程序员共同进步


在线服务QQ:99923144 随时恭候您的光临
首页 基础知识 WIN系统 组件使用 组件开发 数据库 ACTIVEX 多媒体技术 网络技术 关于
文章类别:网络技术    你尚未登陆,会员功能无法使用,请从 网站首页 登陆。
  UrlDownloadToFile下载程序的进度提示  
 

Delphi编写下载程序:UrlDownloadToFile的进度提示

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;

interface

uses
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;

implementation

constructor 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

 

在线服务QQ:99923144 Delphi程序员QQ群(139442)
Delphi知识中心 www.delphi.ee 最专业的Delphi技术资料网站