WebApp.exe Enables User to Move WebBrowser Ctrl

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Article ID: 189634 - View products that this article applies to.
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When hosting the Internet Explorer 4.0x WebBrowser control, it is possible to move the control to both virtual and file folders on the user's local computer. These are folders such as the desktop and My Computer. The problem is that when the user opens a folder in the control, a new Internet Explorer window is opened to display the contents of the selected folder. This might not always be the desired behavior.

To solve this problem, the host application must respond to and handle a Dynamic Data Exchange (DDE) conversation that is initiated by the control when the control calls ShellExecuteEx. WebApp.exe is a sample application that hosts the Internet Explorer 4.0x WebBrowser control that is initially set to the user's desktop. It demonstrates how to establish the DDE conversation, get the DDE command string, parse the DDE command string, and access and free the PIDL that is included in the DDE command. It also handles the special cases described in the MORE INFORMATION section.


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Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. For folders that exist in the file system, the path name can be retrieved from the DDE command and the WebBrowser control can be moved to the new folder by name. However, with virtual folders (such as My Computer), there is no path contained in the DDE command. In these cases, you need to move the control to an ITEMIDLIST pointer (PIDL), which is also included in the DDE command.

The host application is always responsible for freeing the PIDL, whether a folder name is included or not. This PIDL is created in shared memory by the shell so that the PIDL can be used between different processes. Because of this, you need to use special functions to access and free the PIDL. Unfortunately, these functions are not public and must be loaded by ordinal number.

There are two other special cases that you also need to consider. The first is when the user selects Explore instead of Open. In this case, the host application will not know the actual command until the DDE conversation has already been established. By this time, it is too late to allow the DDE conversation to be handled by the default shell implementation. To work around this, the host application must call ShellExecuteEx itself to get the default behavior. While doing this, it must prevent itself from responding the new DDE conversation.

The second special case that you must handle is when another application calls ShellExecuteEx to navigate to a folder. This can happen if the user Selects Run from the Start Menu and types in a folder name, like "C:\". This triggers a call to ShellExecuteEx. In this case, the host application must not respond to the DDE conversation. To avoid this, the host application must only respond to DDE conversations that are being initiated by a window that is in the same process as the host application. This can be determined by getting the process ID of the window handle that is passed in the WM_DDE_INITITIATE message. If the window's process ID is not the same as the host application's process ID, the host application should simply return 0 from the WM_DDE_INITITIATE message.


Article ID: 189634 - Last Review: July 11, 2005 - Revision: 3.4
  • Microsoft Platform Software Development Kit-January 2000 Edition, when used with:
    • Microsoft Windows 95
    • Microsoft Windows NT 4.0
    • Microsoft Windows 2000 Standard Edition
    • Microsoft Internet Client Software Development Kit 4.0
    • Microsoft Internet Client Software Development Kit 4.01
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