Introduction
Sometimes when you are using the IE Browser Control inside of a C++ application, you need to get access to the HTML elements.
We can do it by using standard COM objects like IWebBrowser2
, IHTMLDocument2
, etc.
By this method, we can easily implement features like click button, click anchor, get input string, get HTML text, etc. Unfortunately, Microsoft did not provide similar objects for JavaScript.
At any case, to make control for a JavaScript object inside of an HTML page is possible by using the traditional COM approach. This article describes the class CWebPage
which allows
to do it and a technique to call a JavaScript function from C++ code.
How to do
As a result of using the presented class, it will be easy to call any JavaScript function from C++ code. For implementing this feature,
we should get a pointer to the IHTMLDocument2
interface. If we are using the CHtmlView
class from MFC, we can get one by using the member function
CHtmlView::GetHtmlDocument()
. In the case of using IWebBrowser
or IWebBrowser2
components, the function
get_Document
will bring us the desired interface. Here is an example:
CComPtr<IDispatch> spDisp = CHtmlView::GetHtmlDocument();
m_webPage.SetDocument(spDisp);
The rest of the things will be done by the CWebPage
class. Here is an example of a JavaScript call without parameters:
m_webPage.CallJScript("Welcome");
An example of a JavaScript call with two parameters will looks like:
m_webPage.CallJScript("Miltiply","2.34","3.32");
The class implementation
class CWebPage
{
public:
CWebPage();
virtual ~CWebPage();
bool SetDocument(IDispatch* pDisp);
LPDISPATCH GetHtmlDocument() const;
const CString GetLastError() const;
bool GetJScript(CComPtr<IDispatch>& spDisp);
bool GetJScripts(CComPtr<IHTMLElementCollection>& spColl);
CString ScanJScript(CString& strAText,CStringArray& args);
bool CallJScript(const CString strFunc);
bool CallJScript(const CString strFunc,const CString strArg1);
bool CallJScript(const CString strFunc,const CString strArg1,
const CString strArg2);
bool CallJScript(const CString strFunc,const CString strArg1,
const CString strArg2,const CString strArg3);
bool CallJScript(const CString strFunc,const CStringArray& paramArray);
protected:
CComPtr<IHTMLDocument2> m_spDoc;
};
Calling technique
The above mentioned technique can be split into the following steps:
- Getting a pointer to the
IHTMLDocument2
interface. - Getting
IDispatch
for the JavaScript object in the HTML document. - Getting the
DISPID
for the given name of the JavaScript function. - Putting the parameters to the
DISPPARAM
structure. - Calling the JavaScript function by using the
Invoke
method of the IDispatch
interface.
Here is an example of getting an IDispatch
pointer to the JavaScript objects:
bool CWebPage::GetJScript(CComPtr<IDispatch>& spDisp)
{
HRESULT hr = m_spDoc->get_Script(&spDisp);
ATLASSERT(SUCCEEDED(hr));
return SUCCEEDED(hr);
}
And here is the final function to call JavaScript:
CComVariant CWebPage::CallJScript(const CString strFunc,
const CStringArray& paramArray)
{
CComPtr<IDispatch> spScript;
if(!GetJScript(spScript))
{
ShowError("Cannot GetScript");
return false;
}
CComBSTR bstrMember(strFunc);
DISPID dispid = NULL;
HRESULT hr = spScript->GetIDsOfNames(IID_NULL,&bstrMember,1,
LOCALE_SYSTEM_DEFAULT,&dispid);
if(FAILED(hr))
{
ShowError(GetSystemErrorMessage(hr));
return false;
}
const int arraySize = paramArray.GetSize();
DISPPARAMS dispparams;
memset(&dispparams, 0, sizeof dispparams);
dispparams.cArgs = arraySize;
dispparams.rgvarg = new VARIANT[dispparams.cArgs];
dispparams.cNamedArgs = 0;
for( int i = 0; i < arraySize; i++)
{
CComBSTR bstr = paramArray.GetAt(arraySize - 1 - i); bstr.CopyTo(&dispparams.rgvarg[i].bstrVal);
dispparams.rgvarg[i].vt = VT_BSTR;
}
EXCEPINFO excepInfo;
memset(&excepInfo, 0, sizeof excepInfo);
CComVariant vaResult;
UINT nArgErr = (UINT)-1; hr = spScript->Invoke(dispid,IID_NULL,0,
DISPATCH_METHOD,&dispparams,
&vaResult,&excepInfo,&nArgErr);
delete [] dispparams.rgvarg;
if(FAILED(hr))
{
ShowError(GetSystemErrorMessage(hr));
return false;
}
return vaResult;
}
Notes about the demo
To call a JavaScript function from the demo, you should select a function in the tree in the left window. After this, press the "!" button on the menu bar.
History
- July 07, 2011: Updated download files.
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