4/2/09

COM Standard Interface

We often create shortcuts for program/documents on Windows desktop. This is a two step process. In step 1 we right click on the desktop and select ‘Create Shortcut’ from the menu that pops up. In step 2 we select the file for which the short is to be created. At times we may want to do this procedure programmatically. Here is the program which, shows how this can be achieved.

When we execute the program a dialog box shown in Figure 1 pops up.


Figure 1.

First we need to select the file for which shortcut needs to be created. This can be done by clicking the ‘browse’ button in the dialog. When we do so the function OnButton1( ) gets called. This function pops up a file dialog and permits the user to select a file. The selected file name and complete path is then retrieved using the functions CFileDialog::GetFileTitle( ) and CFileDialog::Get-PathName( ). The selected file name is then displayed in the edit box of dialog shown in Figure 1.

Now to create a shortcut for this file you need to click the ‘Create Shortcut’ button from the dialog. This leads to a call to OnButton2( ). In this function we have retrieved the data of the name ‘Desktop’ from the registry key HKEY_CURRENT_US-ER\Software\Microsoft\Windows\Current Version\Explorer\Shell Folders’. This has been achieved through calls to API functions RegOpenKeyEx( ) and RegQueryValueEx( ). Next we have built three CString objects namely filename, linkname and descname. If the browsed file has a name ‘c:\about.cpp’ then these CString objects would hold ‘c:\about.cpp’, ‘c:\Windows\desktop\about.lnk’, and ‘shortcut to about’.

Lastly to automatically create the shortcut, the function createshortcut( ) is called. In this function we have created a COM object with CLSID CLSID_ShellLink and an interface ID called IID_ IShellLink. Then using QueryInterface( ) we have enquired whether this component has implemented an IPersistFile interface. If it has then we call the functions SetPath( ) and SetDescription( ) of IShellLink interface and Save( ) of IPersistFile interface. Of these, the SetPath( ) function sets the path and filename of a shell link object, whereas the SetDescription( ) function.sets the description string for a shell link object. The Save( ) function saves the object into the specified file. Lastly the Release( ) function has been called to decrement the reference count of the specified interface.

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