C++如何调用JS函数

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:


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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:


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m_webPage.CallJScript("Welcome");

An example of a JavaScript call with two parameters will looks like:


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m_webPage.CallJScript("Miltiply","2.34","3.32");

The class implementation

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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:


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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:


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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;
}