Board index » cppbuilder » TccpWebBrowser event problem

2007-04-27 11:34:23 PM
cppbuilder63
Hi,
I added a form with a TccpWebBrowser to my application to show some news
at start-up.
I try to use the OnNavigateError to check if it is possible to load the
html news page from the server. If not I want to load a page from the
local app directory to inform the user that he must be online to read
the news.
I tried the following code:
void __fastcall TFormNews::LoadPage(const WideString url, const
WideString local_url)
{
LocalURL = local_url;
CppWebBrowser1->Navigate(url);
CppWebBrowser1->Refresh();
if (!FConnected)
CppWebBrowser1->Navigate(LocalURL);
ShowModal();
}
The event handler of OnNavigateError sets the FConnect to false:
void __fastcall TFormNews::CppWebBrowser1NavigateError(TObject *Sender,
LPDISPATCH pDisp, Variant *URL, Variant *Frame, Variant *StatusCode,
VARIANT_BOOL *Cancel)
{
// test if event is fired
if (*Cancel)
ShowMessage("Cancel = true");
else
ShowMessage("Cancel = false");
FConnected = false;
}
Refresh() fires the OnNavigateError event but FConnect is not set to
false if the program reaches the if-statement. If I include a
ShowMessage("Stop!") between the Refresh() and the if-statement then all
works fine! I see from the ShowMessage windows that ShowMessage("Stop!")
arrives before the ShowMessage from the OnNavigateError event handler.
How can I tell the program to wait until the OnNavigateError event
handler has finished? Or is there another solution?
First I didn't insert the Refresh(), then OnNavigateError event is fired
only by ShowModal(), not by Navigate()!!
Thank in advance for any help.
Kind regards
Rolf
 

"Rolf Fankhauser" < XXXX@XXXXX.COM >wrote in message
void __fastcall TFormNews::LoadPage(const WideString &url, const
WideString &local_url)
You have to wait for the events to be triggered in order to know
whether it succeeded or not. You are not waiting for the events, so
you are accessing it too soon after Navigate() exits.
Try this instead:
WideString LocalURL;
bool LoadingLocal;
void __fastcall TFormNews::LoadPage(const WideString &url, const
WideString &local_url)
{
LocalURL = local_url;
LoadingLocal = false;
CppWebBrowser1->Navigate(url);
}
void __fastcall TFormNews::CppWebBrowser1NavigateError(TObject
*Sender, LPDISPATCH pDisp, Variant *URL, Variant *Frame, Variant
*StatusCode, VARIANT_BOOL *Cancel)
{
if( !LoadingLocal )
{
// error loading remote url, load local file next...
LoadingLocal = true;
CppWebBrowser1->Navigate(LocalURL);
}
else
// error loading local file...
}
void __fastcall TFormNews::CppWebBrowser1DocumentComplete(TObject*
Sender, LPDISPATCH pDisp, TVariant *URL)
{
ShowModal();
}
'if' statement is reached.
runs a secondary message queue until the TForm is closed. By calling
ShowMessage(), you are allowing the TCppWebBrowser a chance to process
the pending messages it needs to trigger its events. Without the
ShowMessage(), no message processing is being performed in your code.
Which is why I changed your code in my example above to make
LoadPage() always exit immediately, in order to return control to the
main message queue and allow the normal flow of message processing to
occur.
Gambit
 

"Rolf Fankhauser" < XXXX@XXXXX.COM >wrote in message
told you how to make it work properly. The TTimer only masks the
issue, it does not solve it.
Gambit
 

{smallsort}

Remy,
Thanks for your solution. I see the point. But from my tries so far I
recognized that Navigate() didn't fire the OnNavigateError event in any
case. I had to add Refresh().
But In the meantime I solved the problem by adding a TTimer. After
loading the page the program waits 500 ms to be sure that the event
handler of
OnNavigateError is finished. After that FConnect is correctly set.
I didn't try if I can wait a shorter time but it works. Your solution
would be better.
void __fastcall TFormNews::LoadPage(const WideString &url, const
WideString &local_url, double *last_read, bool read_always, bool
*read_first)
{
ReadFirst = read_first;
ReadAlways = read_always;
LocalURL = local_url;
NewsLastRead = last_read;
CppWebBrowser1->Navigate(url);
CppWebBrowser1->Refresh();
Timer1->Enabled = true;
}
//---------------------------------------------------------------------------
// after waiting until the event handler of OnNavigateError is finished
void __fastcall TFormNews::Timer1Timer(TObject *Sender)
{
Timer1->Enabled = false;
if (!FConnected)
{
if (!ReadAlways)
if (!*ReadFirst)
return;
else
{
CppWebBrowser1->Navigate(LocalURL);
*ReadFirst = false;
CppWebBrowser1->Refresh();
}
}
else
if (!ReadAlways) // if Help / News chosen
if (!NewsAreAdded(NewsLastRead)) return;
ShowModal();
}
 

Remy Lebeau (TeamB) wrote:
solution. Thanks again!

I implemented your solution but the OnDocumentComplete event does not
fire in both cases (remote and local loading). So no form is shown.
Did I forget to set a special property of TCppWebBrowser?
I use CBuilder 6, IE 7 and Windows XP.
Remy Lebeau (TeamB) wrote:

I use now the OnNavigateComplete2 event instead of the
OnDocumentComplete event. There remains one little problem:
If LoadPage() is called in off-line mode (local page is loaded) a second
time (it is called at start-up and can be called by a menu item) then an
empty form is shown. If this form is closed, the form is shown again
with the right contents.
This doesn't happen on-line (if the remote page is loaded).
void __fastcall TFormNews::CppWebBrowser1NavigateComplete2(TObject *Sender,
LPDISPATCH pDisp, Variant *URL)
{
if (!ReadAlways) // at start-up
if (LoadingLocal) {
if (!*ReadFirst)
return; // already shown
else
*ReadFirst = false;
}
else
if (!NewsAreAdded(NewsLastRead))
return;
ShowModal();
}
ReadAlways is true if LoadPage is invoked by the menu item.
ReadFirst is true if the local page is never shown at start-up.
NewsAreAdded() checks if the update date of the remote page is newer
than the date of the last reading of the remote page. This prevents
multiple display of the news form at start-up if news haven't changed.
Rolf Fankhauser wrote:

Remy Lebeau (TeamB) wrote:
is not reachable (I have this situation at the moment) that the event
NavigateError is not fired! So nothing happens.
Rolf