SAMPLE: IEHelper-Attaching to Internet Explorer 4.0 by Using a Browser Helper Object

In order to attach to a running instance of Internet Explorer 4.0, you can use a "Browser Helper Object." A "Browser Helper Object" is a DLL that will attach itself to every new instance of Internet Explorer 4.0. You can use this feature to gain access to the object model of a particular running instance of Internet Explorer. You can also use this feature to get events from an instance of Internet Explorer 4.0.

This article also points to a sample that demonstrates how to implement a Browser Helper Object.

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Browser Helper Objects

When an instance of Internet Explorer 4.0 is started, it looks in the registry for CLSIDs stored under the following key: If this key exists and there are CLSIDs listed under it, Internet Explorer will use CoCreateInstance() to try to create an instance of each object listed as a subkey under this key. Note that the CLSID of the object you create must be listed as a subkey and not a named value.

For example, imagine that the following entry exists in the registry, HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\{CE7C3CF0-4B15-11D1-ABED-709549C10000}. Internet Explorer will try to create an instance of the object pointed to by the CLSID {CE7C3CF0-4B15- 11D1-ABED-709549C10000} each time Internet Explorer starts.

These registry keys can be created manually or through the self registration portion of your COM application.

There are some requirements when creating a Browser Helper Object

• The application that you create must be an in-proc server (that is, DLL).
• This DLL must implement IObjectWithSite.
• The IObjectWithSite::SetSite() method must be implemented. It is through this method that your application receives a pointer to Internet Explorer's IUnknown. (Internet Explorer actually passes a pointer to IWebBrowser2 but the implementation of SetSite() receives a pointer to IUnknown.) You can use this IUnknown pointer to automate Internet Explorer or to sink events from Internet Explorer.
• It must be registered as a Browser Helper Object as described above.

WARNING: Internet Explorer will create an instance of each Browser Helper Object listed in the registry every time a new instance of Internet Explorer is started. This means that if you have Active Desktop installed, the Browser Helper Objects will be loaded every time you open a new folder as well as when the browser itself is started.