Question

Example:

1. I navigate to http://www.stackoverflow.com with my web browser control
2. there’s a link to FAQ in the top bar, with target https://stackoverflow.com/faq
3. I need to redirect e.g. to the http://math.stackexchange.com when I click the FAQ link

Answer 1

The easiest way, as kobik suggested is to use TWebBrowser.OnBeforeNavigate2 event. Here is the example.

procedure TForm1.WebBrowser1BeforeNavigate2(ASender: TObject;
  const pDisp: IDispatch; var URL, Flags, TargetFrameName, PostData,
  Headers: OleVariant; var Cancel: WordBool);
begin
  if URL = 'https://stackoverflow.com/faq' then
  begin
    // setting this flag to True will cancel the current navigation
    Cancel := True;

    // changing this declared parameter doesn't affect anything
    // I've used it just because it's already declared
    URL := 'http://math.stackexchange.com';

    // interrupt all pending navigations and stop dynamic page elements
    (pDisp as IWebBrowser2).Stop;

    // and navigate to the target URL
    (pDisp as IWebBrowser2).Navigate2(URL, Flags, TargetFrameName, PostData, Headers);
  end;
end;

There’s another, more complicated method how to achieve the same. It’s about using the IDocHostUIHandler interface. Except the control of the menus and toolbars visibility, context menu configuration and some events it provides, let’s say, the redirect capability.

To be more specific, it’s the IDocHostUIHandler.TranslateUrl method. This method enables the host to modify the URL to be loaded. It exposes the input URL where the web browser control is going to navigate and the output URL where you redirect it, if you want.

The following example shows the implementation of the IDocHostUIHandler.TranslateUrl method. Please note that I’ve used the interposed class so if you put this code into your unit, only those web browsers on the form or those created in this unit dynamically will get this behavior.

If you click on the Button1 you’ll be navigated to the http://www.stackoverflow.com and if you click on the FAQ link which is directed to the https://stackoverflow.com/faq you’ll be redirected to the http://math.stackexchange.com.

unit Unit1;

interface

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

type
  PDocHostUIInfo = ^TDocHostUIInfo;
  TDocHostUIInfo = record
    cbSize: ULONG;
    dwFlags: DWORD;
    dwDoubleClick: DWORD;
end;

// *********************************************************************//
// Interface: IDocHostUIHandler
// Flags:     (0)
// GUID:      {BD3F23C0-D43E-11CF-893B-00AA00BDCE1A}
// *********************************************************************//
  IDocHostUIHandler = interface(IUnknown)
    ['{BD3F23C0-D43E-11CF-893B-00AA00BDCE1A}']
    function ShowContextMenu(const dwID: DWORD; const ppt: PPoint;
      const pcmdtReserved: IUnknown; const pdispReserved: IDispatch): HRESULT; stdcall;
    function GetHostInfo(var pInfo: TDocHostUIInfo): HRESULT; stdcall;
    function ShowUI(const dwID: DWORD; const pActiveObject: IOleInPlaceActiveObject;
      const pCommandTarget: IOleCommandTarget; const pFrame: IOleInPlaceFrame;
      const pDoc: IOleInPlaceUIWindow): HRESULT; stdcall;
    function HideUI: HRESULT; stdcall;
    function UpdateUI: HRESULT; stdcall;
    function EnableModeless(const fEnable: BOOL): HRESULT; stdcall;
    function OnDocWindowActivate(const fActivate: BOOL): HRESULT; stdcall;
    function OnFrameWindowActivate(const fActivate: BOOL): HRESULT; stdcall;
    function ResizeBorder(const prcBorder: PRect; const pUIWindow: IOleInPlaceUIWindow;
      const fRameWindow: BOOL): HRESULT; stdcall;
    function TranslateAccelerator(const lpMsg: PMSG; const pguidCmdGroup: PGUID;
      const nCmdID: DWORD): HRESULT; stdcall;
    function GetOptionKeyPath(var pchKey: POleStr; const dw: DWORD): HRESULT; stdcall;
    function GetDropTarget(const pDropTarget: IDropTarget; out ppDropTarget: IDropTarget): HRESULT; stdcall;
    function GetExternal(out ppDispatch: IDispatch): HRESULT; stdcall;
    function TranslateUrl(const dwTranslate: DWORD; const pchURLIn: POleStr; var ppchURLOut: POleStr): HRESULT; stdcall;
    function FilterDataObject(const pDO: IDataObject; out ppDORet: IDataObject): HRESULT; stdcall;
  end;

  TWebBrowser = class(SHDocVw.TWebBrowser, IDocHostUIHandler)
  private
    function ShowContextMenu(const dwID: DWORD; const ppt: PPoint;
      const pcmdtReserved: IUnknown; const pdispReserved: IDispatch): HRESULT; stdcall;
    function GetHostInfo(var pInfo: TDocHostUIInfo): HRESULT; stdcall;
    function ShowUI(const dwID: DWORD; const pActiveObject: IOleInPlaceActiveObject;
      const pCommandTarget: IOleCommandTarget; const pFrame: IOleInPlaceFrame;
      const pDoc: IOleInPlaceUIWindow): HRESULT; stdcall;
    function HideUI: HRESULT; stdcall;
    function UpdateUI: HRESULT; stdcall;
    function EnableModeless(const fEnable: BOOL): HRESULT; stdcall;
    function OnDocWindowActivate(const fActivate: BOOL): HRESULT; stdcall;
    function OnFrameWindowActivate(const fActivate: BOOL): HRESULT; stdcall;
    function ResizeBorder(const prcBorder: PRect; const pUIWindow: IOleInPlaceUIWindow;
      const fRameWindow: BOOL): HRESULT; stdcall;
    function TranslateAccelerator(const lpMsg: PMSG; const pguidCmdGroup: PGUID;
      const nCmdID: DWORD): HRESULT; stdcall;
    function GetOptionKeyPath(var pchKey: POleStr; const dw: DWORD): HRESULT; stdcall;
    function GetDropTarget(const pDropTarget: IDropTarget; out ppDropTarget: IDropTarget): HRESULT; stdcall;
    function GetExternal(out ppDispatch: IDispatch): HRESULT; stdcall;
    function TranslateUrl(const dwTranslate: DWORD; const pchURLIn: POleStr; var ppchURLOut: POleStr): HRESULT; stdcall;
    function FilterDataObject(const pDO: IDataObject; out ppDORet: IDataObject): HRESULT; stdcall;
  end;

type
  TForm1 = class(TForm)
    Button1: TButton;
    WebBrowser1: TWebBrowser;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function TWebBrowser.ShowContextMenu(const dwID: DWORD; const ppt: PPoint;
  const pcmdtReserved: IUnknown; const pdispReserved: IDispatch): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.GetHostInfo(var pInfo: TDocHostUIInfo): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.ShowUI(const dwID: DWORD; const pActiveObject: IOleInPlaceActiveObject;
  const pCommandTarget: IOleCommandTarget; const pFrame: IOleInPlaceFrame;
  const pDoc: IOleInPlaceUIWindow): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.HideUI: HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.UpdateUI: HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.EnableModeless(const fEnable: BOOL): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.OnDocWindowActivate(const fActivate: BOOL): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.OnFrameWindowActivate(const fActivate: BOOL): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.ResizeBorder(const prcBorder: PRect;
  const pUIWindow: IOleInPlaceUIWindow; const fRameWindow: BOOL): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.TranslateAccelerator(const lpMsg: PMSG;
  const pguidCmdGroup: PGUID; const nCmdID: DWORD): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.GetOptionKeyPath(var pchKey: POleStr; const dw: DWORD): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.GetDropTarget(const pDropTarget: IDropTarget;
  out ppDropTarget: IDropTarget): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.GetExternal(out ppDispatch: IDispatch): HRESULT;
begin
  Result := E_NOTIMPL;
end;

function TWebBrowser.TranslateUrl(const dwTranslate: DWORD;
  const pchURLIn: POleStr; var ppchURLOut: POleStr): HRESULT;
begin
  // pchURLIn is the URL where the browser is going to navigate
  // ppchURLOut is the URL where the browser will navigate

  if pchURLIn = 'https://stackoverflow.com/faq' then
    ppchURLOut := 'http://math.stackexchange.com';

  Result := S_OK;
end;

function TWebBrowser.FilterDataObject(const pDO: IDataObject;
  out ppDORet: IDataObject): HRESULT;
begin
  Result := E_NOTIMPL;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  WebBrowser1.Navigate('http://www.stackoverflow.com');
end;

end.