JavaScript Calls from C++

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本文转自：

http://www.codeguru.com/Cpp/I-N/ieprogram/article.php/c4399

http://www.codeguru.com/cpp/i-n/ieprogram/article.php/c4399/JavaScript-Calls-from-C.htm
http://www.codeproject.com/KB/COM/jscalls.aspx

Introduction

Sometimes, when we are using the IE Browser Control inside of a C++ application, we need to access the HTML elements. We can do it by using standard COM objects such as

IWebBrowser2

,

IHTMLDocument2

, and so forth. By doing this, we easily can implement features such as click button, click anchor, get input string, get HTML text, and so on. Unfortunately, Microsoft did not provide similar objects for JavaScript. In any case, it is possible to make a control for the JavaScript object inside an HTML page by using a traditional COM approach. This article describes the class

CWebPage

that allows you to do it and a technique to call a JavaScript function from C++ code.

How to Do This

As the result of using the presented class, it will be easy to call any JavaScript function from C++ code. To implement 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 member function

CHtmlView::GetHtmlDocument()

. In the case of using the

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");

The example of the JavaScript call with two parameters will look like this:

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 previously mentioned technique splits the following steps:

Getting a pointer to the

IHTMLDocument2

interface.

Getting

IDispatch

for a JavaScript object in an HTML document.

Getting

DISPID

for a given name of a JavaScript function.

Putting parameters to the

DISPPARAM

structure.

Calling a JavaScript function by using the Invoke method of the

IDispatch

interface.

Here is an example of getting a

IDispatch

pointer to the Java Scripts 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)
{
	//Getting IDispatch for Java Script objects
	CComPtr<IDispatch> spScript;
	if(!GetJScript(spScript))
	{
		ShowError("Cannot GetScript");
		return false;
	}
	//Find dispid for given function in the object
	
	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();
	
	//Putting parameters
	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);
		// back reading
		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;      // initialize to invalid arg
	
	//Call JavaScript function
	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 the function in the tree of the left window. After this, press the ! button on the menu bar.

Downloads

Download demo project - 34 Kb
Download source - 3 Kb