Enumerate Top Level Windows

This example illustrates how to list all of the top-level windows currently in use and extract each window's handle, class name, title, and process and thread IDs. It also demonstrates how to use callback functions as well as Setting Tab Stops in a ListBox.

Although this program shows how to perform a number of useful tasks, by itself it is not extremely useful.   To see how to modify this code to simulate the Window's Task List displayed when you hit the Alt-Tab keys, visit my Task List example.

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The EnumWindows API function is used to enumerate all of the existing windows. When you issue EnumWindows you pass it the address of a public function defined in your code using the AddressOf operator. The callback function, which I named fEnumWindowsCallBack, must reside in a .bas module. The operating system calls your function, fEnumWindowsCallBack in this case, for each window and passes it the handle of the identified window. EnumWindows continues until the last top-level window is enumerated or the callback function returns False.

To build the window list, my fEnumWindowsCallBack function examines each window it is passed and retrieves certain information about that window. For starters, it call the GetClassName API to get the name of the class the window belongs to. Next it calls GetWindowText to get the window's caption. Finally, the GetWindowThreadProcessId function is used to return the process ID and thread ID the window is associated with.

This information is displayed in a listbox for simplicity sake. Because the data consists of rows and columns, a grid control comes to mind.  However, it is an easy matter to set Tab stops in a listbox to neatly align the data into columns. To set the Tab stops I use a type safe variation of the SendMessage function which I call SendMessageArray. Sending the LB_SETTABSTOPS message to the listbox with a wParam value of zero clears any existing Tabs. To set the Tabs you need to store the Tab Stops in an array. Then you resend the LB_SETTABSTOPS message. This time wParam is set to the number of tab stops and the lParam value is set to the first element of the tab stop array.

While there is a way to calculate the location of the tab stops, I find the trial and error method to work best. The listbox program referenced above talks about this in more detail.

Download this project and run it to view all top-level windows.