如何异步使用“WinHttp.WinHttpRequest.5.1”？

代码：

var
  WinHttpReq: OleVariant;

procedure TForm1.Button1Click(Sender: TObject);    
begin
  WinHttpReq := CreateOleObject('WinHttp.WinHttpRequest.5.1');
  WinHttpReq.Open('GET', 'http://stackoverflow.com', TRUE); // asynchronously
  WinHttpReq.setRequestHeader('User-Agent', 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0');
  WinHttpReq.Send();
  // HOW to set a callback procedure here and get the response?
end;

注意：我不想导入 mshttp.dll 并使用 TLB。我想通过后期绑定使用它。我还想处理异常情况（如果有）。

EDIT:我接受 TLama 的答案，因为它为我最初提出的问题提供了一个很好的替代方案。另外它有一个很好的示例源。

这是一个非常好的实现带有 IConnectionPoint 事件的 WinHTTPRequest 包装器 https://forums.embarcadero.com/thread.jspa?messageID=168727（附上源代码）。

正如 Stijn 在他的回答中所说，为了防止程序滞后，请使用线程。IWinHttpRequest.Open http://msdn.microsoft.com/en-us/library/windows/desktop/aa383989%28v=vs.85%29.aspx也有异步配置能力，但是很难捕获事件和IWinHttpRequest.WaitForResponse http://msdn.microsoft.com/en-us/library/windows/desktop/aa384064%28v=vs.85%29.aspx即使如此，你的程序也会卡住。

以下是如何将响应文本放入表单的备注框中的简单示例。 请注意，以下示例使用同步模式，您还可以使用以下命令修改超时值IWinHttpRequest.SetTimeouts http://msdn.microsoft.com/en-us/library/windows/desktop/aa384061%28v=VS.85%29.aspx。如果您想像问题中那样使用异步模式，那么您必须等待结果IWinHttpRequest.WaitForResponse http://msdn.microsoft.com/en-us/library/windows/desktop/aa384064%28v=vs.85%29.aspx method.

///////////////////////////////////////////////////////////////////////////////
/////   WinHttpRequest threading demo unit   //////////////////////////////////
///////////////////////////////////////////////////////////////////////////////

unit WinHttpRequestUnit;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ActiveX, ComObj, StdCtrls;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

///////////////////////////////////////////////////////////////////////////////
/////   THTTPRequest - TThread descendant for single request   ////////////////
///////////////////////////////////////////////////////////////////////////////

type
  THTTPRequest = class(TThread)
  private
    FRequestURL: string;
    FResponseText: string;
    procedure Execute; override;
    procedure SynchronizeResult;
  public
    constructor Create(const RequestURL: string);
    destructor Destroy; override;
  end;

///////////////////////////////////////////////////////////////////////////////
/////   THTTPRequest.Create - thread constructor   ////////////////////////////
///////////////////////////////////////////////////////////////////////////////

// RequestURL - the requested URL

constructor THTTPRequest.Create(const RequestURL: string);
begin
  // create and start the thread after create
  inherited Create(False);
  // free the thread after THTTPRequest.Execute returns
  FreeOnTerminate := True;
  // store the passed parameter into the field for future use
  FRequestURL := RequestURL;
end;

///////////////////////////////////////////////////////////////////////////////
/////   THTTPRequest.Destroy - thread destructor   ////////////////////////////
///////////////////////////////////////////////////////////////////////////////

destructor THTTPRequest.Destroy;
begin
  inherited;
end;

///////////////////////////////////////////////////////////////////////////////
/////   THTTPRequest.Execute - thread body   //////////////////////////////////
///////////////////////////////////////////////////////////////////////////////

procedure THTTPRequest.Execute;
var
  Request: OleVariant;
begin
  // COM library initialization for the current thread
  CoInitialize(nil);
  try
    // create the WinHttpRequest object instance
    Request := CreateOleObject('WinHttp.WinHttpRequest.5.1');
    // open HTTP connection with GET method in synchronous mode
    Request.Open('GET', FRequestURL, False);
    // set the User-Agent header value
    Request.SetRequestHeader('User-Agent', 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0');
    // sends the HTTP request to the server, the Send method does not return
    // until WinHTTP completely receives the response (synchronous mode)
    Request.Send;
    // store the response into the field for synchronization
    FResponseText := Request.ResponseText;
    // execute the SynchronizeResult method within the main thread context
    Synchronize(SynchronizeResult);
  finally
    // release the WinHttpRequest object instance
    Request := Unassigned;
    // uninitialize COM library with all resources
    CoUninitialize;
  end;
end;

///////////////////////////////////////////////////////////////////////////////
/////   THTTPRequest.SynchronizeResult - synchronization method   /////////////
///////////////////////////////////////////////////////////////////////////////

procedure THTTPRequest.SynchronizeResult;
begin
  // because of calling this method through Synchronize it is safe to access
  // the VCL controls from the main thread here, so let's fill the memo text
  // with the HTTP response stored before
  Form1.Memo1.Lines.Text := FResponseText;
end;

///////////////////////////////////////////////////////////////////////////////
/////   TForm1.Button1Click - button click event   ////////////////////////////
///////////////////////////////////////////////////////////////////////////////

// Sender - object which invoked the event

procedure TForm1.Button1Click(Sender: TObject);
begin
  // because the thread will be destroyed immediately after the Execute method
  // finishes (it's because FreeOnTerminate is set to True) and because we are
  // not reading any values from the thread (it fills the memo box with the
  // response for us in SynchronizeResult method) we don't need to store its
  // object instance anywhere as well as we don't need to care about freeing it
  THTTPRequest.Create('http://stackoverflow.com');
end;

end.