Binding to Internet Explorer events: bug in Typelibrary

Article
05/17/2005

I was using the web browser control and getting some errors when binding to its events. This can be duplicated with the code below.

To generate the event class, open the object browser (Tools->Object Browser) and select the Microsoft Web Browser Control. Navigate to the DWebBrowserEvents2 interface and drag and drop it onto an open PRG editor window.

The object browser reads the interface definition from the type library for the chosen COM object and defines a class with the appropriate method signatures for you.

Then I added a couple lines to instantiate the web browser, the event class, and bind them together.

Running the code highlights the FileDownload method and gives the error: “Must specify additional parameters.”

Because this error is generated by an external object (IE) calling VFP, but before even reaching any VFP user code, a TRY/CATCH or error handler doesn’t help.

Further investigation showed that the FileDownload method of the DWebBrowserEvents2 interface shows that there is one parameter specified in the Type library.

[id(0x0000010e), helpstring("Fired to indicate the File Download dialog is opening")]

void FileDownload([in, out] VARIANT_BOOL* Cancel);

However, IE is calling with 2 parameters. The MSDN documentation for this method shows 2 parameters:

 void FileDownload(

     VARIANT_BOOL *&ActiveDocument,

     VARIANT_BOOL *&Cancel

);

This KB article has more info. In particular, it states “any development tool that generates event handlers that are based on the type library cannot properly sink the event. “ The article itself has to do with .NET interop with the web browser control, so C# and VB.Net have the same problem.

Rick Strahl’s article also mentions this bug.

VFP internally reads the typelib and tries to match the number and type of parameters for each method. If the number of parameters aren’t exactly the same, VFP triggers an error message.

Perhaps a fix to this on the VFP side would be to relax the restriction that the number of parameters match exactly: just trigger an error if the number of parameters in the TypeLib is greater than the number defined in the VFP method. This change will allow the user to add more parameters to the implemented methods, which would fix this issue and also allow the method to be called internally with additional parameter(s).

oIe=

CREATEOBJECT("internetexplorer.application")

oIe.

visible=1

oEvents =

NEWOBJECT("webEvents")

EVENTHANDLER(oIE,oEvents)

oIe.navigate2("www.msn.com")

DEFINE CLASS

webEvents AS custom

IMPLEMENTS

DWebBrowserEvents2 IN "c:\windows\system32\shdocvw.dll"

PROCEDURE logit(cstr as String)

?cstr

PROCEDURE init

this

.logit(PROGRAM())

PROCEDURE DWebBrowserEvents2_StatusTextChange(Text AS STRING) AS VOID;

HELPSTRING "Statusbar text changed."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_ProgressChange(Progress AS Number, ProgressMax AS Number) AS VOID;

HELPSTRING "Fired when download progress is updated."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_CommandStateChange(Command AS Number, Enable AS LOGICAL) AS VOID;

HELPSTRING "The enabled state of a command changed."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_DownloadBegin() AS VOID;

HELPSTRING "Download of a page started."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_DownloadComplete() AS VOID;

HELPSTRING "Download of page complete."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_TitleChange(Text AS STRING) AS VOID;

HELPSTRING "Document title changed."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_PropertyChange(szProperty AS STRING) AS VOID;

HELPSTRING "Fired when the PutProperty method has been called."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_BeforeNavigate2(pDisp AS VARIANT, URL AS VARIANT, Flags AS VARIANT, TargetFrameName AS VARIANT, PostData AS VARIANT, Headers AS VARIANT, Cancel AS LOGICAL @) AS VOID;

HELPSTRING "Fired before navigate occurs in the given WebBrowser (window or frameset element). The processing of this navigation may be modified."

this.logit(PROGRAM()+" "+url+" "+TRANSFORM(flags))

ENDPROC

PROCEDURE

DWebBrowserEvents2_NewWindow2(ppDisp AS VARIANT @, Cancel AS LOGICAL @) AS VOID;

HELPSTRING "A new, hidden, non-navigated WebBrowser window is needed."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_NavigateComplete2(pDisp AS VARIANT, URL AS VARIANT) AS VOID;

HELPSTRING "Fired when the document being navigated to becomes visible and enters the navigation stack."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_DocumentComplete(pDisp AS VARIANT, URL AS VARIANT) AS VOID;

HELPSTRING "Fired when the document being navigated to reaches ReadyState_Complete."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnQuit() AS VOID;

HELPSTRING "Fired when application is quiting."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnVisible(Visible AS LOGICAL) AS VOID;

HELPSTRING "Fired when the window should be shown/hidden"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnToolBar(ToolBar AS LOGICAL) AS VOID;

HELPSTRING "Fired when the toolbar should be shown/hidden"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnMenuBar(MenuBar AS LOGICAL) AS VOID;

HELPSTRING "Fired when the menubar should be shown/hidden"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnStatusBar(StatusBar AS LOGICAL) AS VOID;

HELPSTRING "Fired when the statusbar should be shown/hidden"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnFullScreen(FullScreen AS LOGICAL) AS VOID;

HELPSTRING "Fired when fullscreen mode should be on/off"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_OnTheaterMode(TheaterMode AS LOGICAL) AS VOID;

HELPSTRING "Fired when theater mode should be on/off"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_WindowSetResizable(Resizable AS LOGICAL) AS VOID;

HELPSTRING "Fired when the host window should allow/disallow resizing"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_WindowSetLeft(Left AS Number) AS VOID;

HELPSTRING "Fired when the host window should change its Left coordinate"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_WindowSetTop(Top AS Number) AS VOID;

HELPSTRING "Fired when the host window should change its Top coordinate"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_WindowSetWidth(Width AS Number) AS VOID;

HELPSTRING "Fired when the host window should change its width"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_WindowSetHeight(Height AS Number) AS VOID;

HELPSTRING "Fired when the host window should change its height"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_WindowClosing(IsChildWindow AS LOGICAL, Cancel AS LOGICAL @) AS VOID;

HELPSTRING "Fired when the WebBrowser is about to be closed by script"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_ClientToHostWindow(CX AS Number @, CY AS Number @) AS VOID;

HELPSTRING "Fired to request client sizes be converted to host window sizes"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_SetSecureLockIcon(SecureLockIcon AS Number) AS VOID;

HELPSTRING "Fired to indicate the security level of the current web page contents"

this.logit(PROGRAM())

ENDPROC

* PROCEDURE DWebBrowserEvents2_FileDownload( Cancel AS LOGICAL @) AS VOID

PROCEDURE DWebBrowserEvents2_FileDownload(fActiveDoc as Logical @, Cancel AS LOGICAL @) AS VOID;

HELPSTRING "Fired to indicate the File Download dialog is opening"

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_NavigateError(pDisp AS VARIANT, URL AS VARIANT, Frame AS VARIANT, StatusCode AS VARIANT, Cancel AS LOGICAL @) AS VOID;

HELPSTRING "Fired when a binding error occurs (window or frameset element)."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_PrintTemplateInstantiation(pDisp AS VARIANT) AS VOID;

HELPSTRING "Fired when a print template is instantiated."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_PrintTemplateTeardown(pDisp AS VARIANT) AS VOID;

HELPSTRING "Fired when a print template destroyed."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_UpdatePageStatus(pDisp AS VARIANT, nPage AS VARIANT, fDone AS VARIANT) AS VOID;

HELPSTRING "Fired when a page is spooled. When it is fired can be changed by a custom template."

this.logit(PROGRAM())

ENDPROC

PROCEDURE

DWebBrowserEvents2_PrivacyImpactedStateChange(bImpacted AS LOGICAL) AS VOID;

HELPSTRING "Fired when the global privacy impacted state changes"

this.logit(PROGRAM())

ENDPROC

ENDDEFINE

Binding to Internet Explorer events: bug in Typelibrary

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