Microsoft KB Archive/175504

= How To Determine Whether a User Is Subscribed to a Channel =

Article ID: 175504

Article Last Modified on 7/1/2004

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APPLIES TO


 * Microsoft Internet Explorer 4.0 128-Bit Edition
 * Microsoft Internet Explorer 4.01 Service Pack 2
 * Microsoft Internet Explorer 5.0
 * Microsoft Internet Explorer 5.5

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This article was previously published under Q175504



SUMMARY
With the introduction of Active Channels in Internet Explorer 4.0, it may be desirable to determine whether a user is already subscribed to a channel, so that a Web page or an application does not redundantly offer users the ability to subscribe to a channel they've already subscribed to.



MORE INFORMATION
This article describes how to check a subscription from C++, Visual Basic, and script.

C++ - using ISubscriptionMgr::IsSubscribed
The code below demonstrates how this can be done using C++, from a console application:
 * 1) include 
 * 2) include 
 * 3) include 
 * 4) include 
 * 5) include 

void main {  ISubscriptionMgr *pSubscriptionMgr; CoInitialize(NULL);

HRESULT hr = CoCreateInstance(CLSID_SubscriptionMgr,                                NULL,                                 CLSCTX_INPROC_SERVER,                                 IID_ISubscriptionMgr,                                 (void**)&pSubscriptionMgr); if (SUCCEEDED(hr)) {     BOOL Bool; BSTR bstrURL = SysAllocString(L"http://test.microsoft.com/tst.cdf"); hr = pSubscriptionMgr->IsSubscribed(bstrURL, &Bool);

pSubscriptionMgr->Release;

char szBuffer[250]; TCHAR szURL[200]; WideCharToMultiByte(CP_ACP, 0, bstrURL, -1, szURL, 200, NULL,                         NULL); if (Bool) wsprintf (szBuffer,"YES, you are subscribed to %s\n",szURL); else wsprintf (szBuffer,"NOPE, you are NOT subscribed to %s\n",                    szURL); cout << szBuffer; SysFreeString (bstrURL); }

CoUninitialize; }

Visual Basic - Using the ShellUIHelper Object
The code below demonstrates how this can be done in a standard Visual Basic application. To use the ShellUIHelper object, use Project->References to add a reference to "Microsoft Internet Controls." Private Sub Form_Load Dim ShlHlpr As ShellUIHelper

Set ShlHlpr = New ShellUIHelper

If ShlHlpr.IsSubscribed("http://test.microsoft.com/tst.cdf") Then MsgBox "You're Subscribed!" Else MsgBox "You're not Subscribed!" End If End Sub Please note that you must install the desktop update that comes with Internet Explorer 4.0x in order to use the ShellUIHelper object.

Script - Using window.external.isSubscribed
The code below demonstrates how this can be done, using JavaScript in an .htm page:  if (window.external.isSubscribed("http://test.microsoft.com/tst.cdf")) alert ("You are subscribed!"); else alert ("You are NOT subscribed!");  Cross-frame security rules apply to this script call. Script in a document can only check to see if the user is subscribed to sites on the same domain.

