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Communication between C++ Silverlight Host and Silverlight Application

, 20 May 2010 CPOL
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It explains how we can call a method defined in Silverlight from Silverlight C++ host.


I would like you to take a look at my previous article Host_Silverlight_In_ATL before continuing with this one. In this article, we will talk about communication between C++ Silverlight host and Silverlight application which means we can call a method of Silverlight app from C++ Silverlight host.


Things to Do in a Silverlight Application

 using System.Windows.Browser;

Use the above mentioned namespace for communication. We will use HTML communication bridge to communicate with the C++ host.

Use the following statement to register the Communicator object. We will get this communicator object in C++ Silverlight host using IDispath.

HtmlPage.RegisterScriptableObject("Communicator", this);

Write another function in Silverlight application which we will call from C++ Silverlight host.

public void SetDataInTextBox(string strData)
	txtData.Text = strData;

The complete code for the Silverlight page is as follows:

using System.Windows.Browser;
namespace SilverlightTestApp
	public partial class MainPage : UserControl
		public MainPage()
			HtmlPage.RegisterScriptableObject("Communicator", this);
		private void ClickMe_Click(object sender, RoutedEventArgs e)
			MessageBox.Show("Button click handler is in Silverlight :)", 
			"SilverlightTestApp", MessageBoxButton.OK);
		public void SetDataInTextBox(string strData)
			txtData.Text = strData;

I am not trying to explain Silverlight development issues here but I would like to say the same things we do for Silverlight and JavaScript interaction. If someone is not familiar with the above code, Google Silverlight and JavaScript interaction. Almost every Silverlight book covers this topic.

C++ Silverlight Host

Add an edit box and a button in your dialog box in ATL application. We will enter some test in the edit box and write some code in the click handler of the button we just added.

Handler function for button click. Getting the user input in strData...

LRESULT CCMainDlg::OnBnClickedBtnSendDataToSilverlight
	(WORD /*wNotifyCode*/, WORD /*wID*/, HWND /*hWndCtl*/, BOOL& /*bHandled*/)
 	CAtlStringW strData;

Now coming to the main point - getting DISPID of Communicator object we just registered in Silverlight app.

IDispatch *pContent;
HRESULT hr = CXcpControlHost::GetXcpControlPtr()->get_Content(&pContent);
CComBSTR bstrMember(L"Communicator");
DISPID dispIDCommunicator = NULL;
hr = pContent->GetIDsOfNames(IID_NULL, &bstrMember, 1, 
	LOCALE_SYSTEM_DEFAULT, &dispIDCommunicator); 
	::MessageBox(NULL, L"Failed to get the DISPID for Communicator", 
		L"Error :(", 0);
	return 0;

Once we have a valid dispID for Communicator object, we are ready to get the IDispatch* for Communicator object. It's a bit tricky here, we will make an invoke call with DISPATCH_PROPERTYGET.

VARIANT pVarResult;
DISPPARAMS dispparams; 
memset(&dispparams, 0, sizeof dispparams);
dispparams.cArgs = 0;
dispparams.rgvarg = NULL;
dispparams.cNamedArgs = 0;
// Getting IDispatch from for Scriptable object exposed by Silverlight Application. 
// Passing dispid for "Communicator" to get its IDispatch* using DISPATCH_PROPERTYGET.
hr = pContent->Invoke(dispIDCommunicator,
&dispparams, &pVarResult, NULL, NULL);
	::MessageBox(NULL, L"Failed to get the IDsipatch* of Communicator", 
		L"Error :(", 0);
	return 0;

IDispatch* pCommunicatorDispatch = pVarResult.pdispVal;

We stored IDispatch* for Communicator in pCommunicatorDispatch. Now we have to play with this pCommunicatorDispatch. This is our key player now, with pCommunicatorDispatch, we will get the DISPID for our exposed method (SetDataInEditBox) from a Silverlight app and then make an Invoke() call to call SetDataInEditBox() by passing that string into that function.

bstrMember = L"SetDataInTextBox";
DISPID dispIDSetDataInTextBox = NULL;
hr = pCommunicatorDispatch->GetIDsOfNames(IID_NULL,&bstrMember,1, 
EXCEPINFO pexcepinfo ;
	dispparams.cArgs = 1;
	dispparams.cNamedArgs = 1;
	dispparams.rgvarg = new VARIANT[1];
	dispparams.rgvarg[0].vt = VT_BSTR;
	dispparams.rgvarg[0].bstrVal = SysAllocString(strData.GetString());
	hr = pCommunicatorDispatch->Invoke(dispIDSetDataInTextBox, 
		&dispparams, &pVarResult,&pexcepinfo,NULL);
	delete [] dispparams.rgvarg;

	if (hr != S_OK)
		::MessageBox(NULL, L"Failed to Invoke Silverlight function", 
			L"Error :(", 0);
		return 0;
	::MessageBox(NULL, L"Failed to get the DISPID for SetDataInTextBox 
		function defined in Silverlight.", L"Error :(", 0);


In this article, I've shown you how to call a function defined in a Silverlight application from C++ Silverlight host.

Hopefully, this article will help you a little bit for Silverlight and C++ interaction.

For questions, comments and remarks, please use the commenting section at the bottom of this article.


  • 20th May, 2010: Initial post


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Syed Aftab Naqvi
Software Developer (Senior)
United States United States
Syed Aftab Hassan Naqvi

Comments and Discussions

Questionquestion about drag and drop Pinmembericexile1-Dec-11 20:08 
QuestionAnd the keyboard ? Pinmembersergiobuonanno4-Nov-11 6:07 
GeneralMy vote of 5 PinmemberMember 340074723-Oct-11 8:32 
Questionunable to load xap file if i use smoothstreaming api to implement the sliverlight application. Pinmemberstevensxiong22-Feb-11 15:55 
AnswerRe: unable to load xap file if i use smoothstreaming api to implement the sliverlight application. Pinmemberhieronymus10029-May-14 3:41 
Generalwindowless and OleDraw PinmemberKnives8922-Jan-11 15:27 
GeneralRe: windowless and OleDraw PinmemberSyed Aftab Naqvi22-Jan-11 17:21 
GeneralRe: windowless and OleDraw [modified] PinmemberKnives8922-Jan-11 22:50 
GeneralNeed code to send data from silverlight to c++ PinmemberMember 184635823-Dec-10 11:55 
GeneralRe: Need code to send data from silverlight to c++ PinmemberSyed Aftab Naqvi2-Jun-11 10:23 
GeneralOnly works within the context of the UI thread Pinmemberdriverscience16-Dec-10 8:30 
GeneralRe: Only works within the context of the UI thread PinmemberSyed Aftab Naqvi22-Jan-11 17:23 
QuestionC# Version? Pinmembertomaten6-Nov-10 9:29 
Generalhelp Pinmemberliuliu27-Jun-10 18:26 
GeneralRe: help PinmemberSyed Aftab Naqvi28-Jun-10 14:11 
GeneralRe: help Pinmemberliuliu29-Jun-10 17:44 
GeneralRe: help PinmemberSyed Aftab Naqvi30-Jun-10 6:57 
GeneralRe: help Pinmemberliuliu30-Jun-10 22:39 
GeneralRe: help PinmemberSyed Aftab Naqvi1-Jul-10 11:45 
GeneralRe: help Pinmemberliuliu1-Jul-10 17:35 
GeneralRe: help PinmemberSyed Aftab Naqvi2-Jul-10 10:54 
GeneralSilverlight 4 - COM integration PinmemberErnest Laurentin24-May-10 11:07 
GeneralRe: Silverlight 4 - COM integration PinmemberSyed Aftab Naqvi24-May-10 11:26 
GeneralRe: Silverlight 4 - COM integration [modified] PinmemberErnest Laurentin24-May-10 20:21 
GeneralRe: Silverlight 4 - COM integration PinmemberSyed Aftab Naqvi25-May-10 11:32 

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