Archive for September, 2004

MSHTML Hosting – Odds & Ends

In this post I wanted to cover some miscellaneous things you may want to do with your embedded WebBrowser. On its own, the IWebBrowser2 interface does not support doing much more than we already covered in previous posts. However, if you start
using the MSHTML DOM interfaces, much more functionality is available. Here is a list of simple things you can implement without too much difficulty:

  • Retrieving HTML from the WebBrowser.
  • Retrieving the HTML of the current selection.
  • Finding text in the HTML and selecting it.
  • Creating an image of the current HTML.

Retrieving HTML from the WebBrowser

There are times when you might want to get the currently loaded HTML from the control. You may want to save it to a file or parse it for information. For this functionality, you have to use the IPersistXxx interfaces. These are the same we used to load HTML into the WebBrowser from memory. The same works in reverse:


IHTMLDocument2* pDoc = ...;
IStream* pMyStream = ...;

IPersistStreamInit* pPersist = 0;
HRESULT hr = pDoc->QueryInterface(IID_IPersistStreamInit, (void**)&pPersist);
if (SUCCEEDED(hr) && pPersist) {
    hr = pPersist->Save(pMyStream, true);
    pPersist->Release();
}

Retrieving the HTML of the current selection

If you want to limit the HTML to just what a user has selected, instead of the entire document, we can use the IHTMLXxx COM interfaces. The first thing you need to do is get access to the IHTMLDocument interface for the current document. IWebBrowser2 gives you access using it’s Document property. The Document property returns an IDispatch interface, so we need to QueryInterface the IDispatch interface for an IHTMLDocument interface, like so (raw C++):


IDispatch* pDocDisp = 0;
HRESULT hr = pWebBrowser->get_Document(&pDocDisp);

IHTMLDocument2* pDoc = 0;
hr = pDocDisp->QueryInterface(IID_IHTMLDocument2, (void**)&pDoc);
if (SUCCEEDED(hr)) {

    //...

    pDoc->Release();
}

pDocDisp->Release();

The IHTMLXxx interfaces follow the W3C DOM specification used for JavaScript very closely. If your familiar with those objects, the IHTMLXxx interface will be easy to grasp. In fact, if you know how to do something using JavaScript, you can duplicate it your compiled code using the IHTMLXxx interfaces.

That said, you can get the current selection as a IHTMLTxtRange from the document element. Once you have a text range, you can retrieve the plain text or HTML text as shown below:


IHTMLDocument2* pDoc = ...;

IHTMLSelectionObject* pSelection = 0;
HRESULT hr = pDoc->get_selection(&pSelection);
if (SUCCEEDED(hr)) {
   IDispatch* pDispRange = 0;
   hr = pSelection->createRange(&pDispRange);
   if (SUCCEEDED(hr)) {
      IHTMLTxtRange* pTextRange = 0;
      hr = pDispRange->QueryInterface(IID_IHTMLTxtRange, (void**)&pTextRange);
      if (SUCCEEDED(hr)) {
         CComBSTR sText;
         pTextRange->get_text(&sText);
         // or
         pTextRange->get_htmlText(&sText);
         //...
         pTextRange->Release();
      }
      pDispRange->Release();
   }
   pSelection->Release();
}

pDoc->Release();

Finding text in the HTML and selecting it

The Google toolbar in IE does this to make it easy to spot keywords found in the page. We are using body and text range objects. This time we are making a IHTMLTxtRange object, not getting the current selection. IHTMLTxtRange has find and select methods that make this task easy. Be sure to check out the parameters for IHTMLTxtRange::findText as they can be used to modify how the text is searched:


IHTMLDocument2* pDoc = ...;
IHTMLElement* pBodyElem = 0;
HRESULT hr = pDoc->get_body(&pBodyElem);
if (SUCCEEDED(hr)) {
   IHTMLBodyElement* pBody = 0;
   hr = pBodyElem->QueryInterface(IID_IHTMLBodyElement, (void**)&pBody);
   if (SUCCEEDED(hr)) {
      IHTMLTxtRange* pTextRange = 0;
      hr = pBody->createTextRange(&pTextRange);
      if (SUCCEEDED(hr)) {
         CComBSTR sText = "findme";
         VARIANT_BOOL bSuccess;
         hr = pTextRange->findText(sText, 0, 0, &bSuccess);
         if (SUCCEEDED(hr) && bSuccess == VARIANT_TRUE)
            pTextRange->select();
         pTextRange->Release();
      }
      pBody->Release();
   }
   pBodyElem->Release();
}

pDoc->Release();

Creating an image of the current HTML

Turning the contents of the WebBrowser into an image is not as straight forward as you may expect. Looking at the IHTMLXxx interfaces does turn up an IHTMLElementRenderer interface. IHTMLElementRenderer contains:

IHTMLElementRender::DrawToDC(HDC hDC);

You can try to use this method, but I have found that it is not very reliable and reacts inconsistently depending on the type of HDC you give it. A more reliable method uses an older OLE method. IViewObject supports the ability to render to an HDC. The IWebBrowser2::Document property can be QueryInterfaced for IViewObject. Two things to note while using this method, (1) you will probably want to turn off the scrollbars and 3D border since they will show up in the image and (2) you will want to resize the WebBrowser to the size of the contained HTML if you want to capture the entire content in the image. You may want to only make these changes temporarily and change them back after the image is captured:


IHTMLDocument2* pDoc = ...;
IHTMLElement* pBodyElem = 0;
HRESULT hr = pDoc->get_body(&pBodyElem);
if (SUCCEEDED(hr)) {
   IHTMLBodyElement* pBody = 0;
   hr = pBodyElem->QueryInterface(IID_IHTMLBodyElement, (void**)&pBody);
   if (SUCCEEDED(hr)) {
      // hide 3D border
      IHTMLStyle* pStyle;
      hr = pBodyElem->get_style(&pStyle);
      if (SUCCEEDED(hr)) {
         pStyle->put_borderStyle(CComBSTR("none"));
         pStyle->Release();
      }

      // hide scrollbars
      pBodyElement->put_scroll(CComBSTR("no"));

      // resize the browser component to the size of the HTML content
      IHTMLElement2* pBodyElement2;
      hr = Body->QueryInterface(IID_IHTMLElement2, (void**)&BodyElement2)
      if (SUCCEEDED(hr)) {
         long iScrollWidth = 0;
         pBodyElement2->get_scrollWidth(&iScrollWidth);

         long iScrollHeight = 0;
         pBodyElement2->get_scrollHeight(&iScrollHeight);

         // these lines depend on your WebBrowser wrapper
         pWebBrowser->SetWidth(iScrollWidth);
         pWebBrowser->SetHeight(iScrollHeight);

         pBodyElement2->Release();

         IViewObject* pViewObject;
         pDoc->QueryInterface(IID_IViewObject, (void**)&pViewObject);
         if (pViewObject) {
            /* however you want to make your image HDC.
               You can size it using iScrollHeight & iScrollWidth */
            HDC hImageDC = ... // could be bitmap or enhanced metafile
            HDC hScreenDC = ::GetDC(0);
            RECT rcSource = {0, 0, iScrollWidth, iScrollHeight};
            hr = pViewObject->Draw(DVASPECT_CONTENT, 1, NULL, NULL,
                                   hScreenDC, hImageDC, rcSource,
                                   NULL, NULL, 0);
            ::ReleaseDC(0, hScreenDC);
            pViewObject->Release();
         }
      }
      pBody->Release();
   }
   pBodyElem->Release();
}

pDoc->Release();

As you can see, there is a lot of things you can do using the MSHTML object model. Some of it can be tricky. Other things just aren’t supported as well as they should be for an application developer. I guess you could say that application developers have their own list of issues for IE.

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MSHTML Hosting – Mozilla

Before moving ahead with the MSHTML hosting posts, I wanted to take a moment to talk about alternatives to WebBrowser. I am sure you are familiar with the Mozilla webbrowser. Started as an open source project by Netscape, Mozilla and its suite of companion projects are quite an achievement. One of the Mozilla projects is an ActiveX wrapper around the rendering engine which conforms to the IWebBrowser2 and DWebBrowserEvents2 COM interfaces. Created and maintained by Adam Lock the project has come along way. There is even minimal support for the IHTMLDocument DOM interfaces.

Everything we have covered in previous posts regarding WebBrowser functionality can be implemented using the Mozilla control as well. With no code changes! Just embed the Mozilla control and your application will not be dependent on Microsoft. Some of us like having choices.

My biggest problem with the Mozilla control is that the project is not moving fast enough to implement more functionality. Honestly, if Mozilla wants to grab more market share, it should be putting more resources on the project. One or two guys is not enough. I know that some people would tell me to just use the native Mozilla C++ classes and interfaces to embed the rendering engine. I am sorry, but there is too much to learn. A very large number of people know, and are comfortable using, ActiveX controls and COM data types. Frameworks have been built to make it easy to use such controls. Why would I want to learn a niche framework? That’s the main reason I have not been able to contribute to the project myself. Its a large investment.

That said, I still love the idea of having choices. The Mozilla control is a great start and if I was writing an application that only need basic features, I would seriously consider using it. I hope very much that the project keeps progressing.

More…

Nick Bradury (author of FeedDemon and TopStyle) on Mozilla control.

Joel Spolsky (of Joel On Software) on why Mozilla should be actively building an ActiveX wrapper.

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MSHTML Hosting – Building UI’s

My last posts have dealt with using the WebBrowser component to display HTML pages inside your application. We have seen how it does not take much to embed the control to create your own little mini-webbrowser. In this post I want to go a little further than building a webbrowser. Lots of applications are using a web-like UI. Applications like Intuit Quicken, Microsoft Outlook and Money actually use the WebBrowser control to achieve their web-like UI’s. Microsoft Office task panes and other inductive UI’s can be developed using the WebBrowser control.

When using the WebBrowser control for building a UI there are a few issues to consider:

  1. Loading the HTML into the control. You most likely will not be using Navigate to load the HTML. In most cases you are dynamically generating the HTML from scratch or from a template loaded from a resource.
  2. Handling mouse and keyboard events. Since you are building a UI, it is very likely that the content will be interactive. There may be edit boxes, push buttons and hyperlinks in the content. You will need to handle those events and respond accordingly.

Loading HTML

The most common (but not the only) way to load HTML from a buffer to the WebBrowser is via streams. Microsoft has a nice example in the WebBrowser reference. A quick Google search will turn up a way to do it in your favorite tool or language. The key points here are:

  1. Navigate to “about:blank”
  2. Wait for the blank document to finish loading
  3. Load your HTML using the IPersistStreamInit method

Step #3 looks like this:


IHTMLDocument2* pDoc = ...;
IStream* pMyStream = ...;

IPersistStreamInit* pPersist = 0;
HRESULT hr = pDoc->QueryInterface(IID_IPersistStreamInit, (void**)&pPersist);
if (SUCCEEDED(hr) && pPersist) {
    hr = pPersist->InitNew();
    if (SUCCEEDED(hr)) {
        hr = pPersist->Load(pMyStream);
    }
    pPersist->Release();
}

Note: I would strongly recommend that any external links you have in your generated HTML (stylesheets or JavaScript) are referenced using absolute paths. Do not use relative paths. The IPersistStreamInit method does not update the control’s base URL. Navigate does update the base URL. Therefore, any relative path will have “about:blank” prepended to it and the control will not likely find your external link.

Handling Events

The ability to handle mouse and keyboard events is critical when creating an interactive UI. There are 2 basic methods to do this with WebBrowser:

  1. Use <A> tags to create hyperlinks with bogus href URL’s. Then use OnBeforeNavigate2 to intercept the bogus URL, cancel the navigation and respond to the mouse click.
  2. Hook your native code to the onclick, onkeypress, or any of the many other JavaScript events.

Method #1 is cheap and easy, but really only works with hyperlinks. In my applications, I create bogus hyperlinks that are easy to parse inside OnBeforeNavigate2 and contain breadcrumbs for me to use when responding to the click. Here is an example:

myapp://edititem/12345

I can look for a constant substring to indicate its my bogus HREF (myapp://). I can figure out the type of action (edititem). I also know which item to edit (12345). The last part could be a database ID or a pointer to an object cast to a long integer. The whole thing even looks like a real URL too.

Method #2 is much more robust, but a little more complicated to implement. There are more steps involved. You will also be working with the IHTMLDocument system and creating IDispatch wrappers. We’ll cover those topics in future posts.

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