Safely Shut Down a Running Application

The Shell command makes it is easy to start an application from Visual Basic. Stopping it is a harder. Many samples use the TerminateProcess function to stop the application. This is dangerous since the application will be shut down abruptly and a loss of data may occur. Even the TerminateProcess documentation warns you not to try this except as a last resort.

Safely stop a process or application that is running.
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Discussion

This program uses the intrinsic Shell command to launch the application whose path you specify. Returned by the Shell command is the Process ID or PID of the shelled application. When you click the End Process button, this program enumerates all top level windows in the system and stores the handles of those windows associated with the shelled application in a collection. It then loops through the collection and sends the WM_CLOSE message to each window using SendMessage.

WM_CLOSE instructs the windows to close in their normal fashion as if you manually closed them. The window may display a confirmation dialog depending on how it handles the close message. To avoid being asked to confirm closing the window, you can send the WM_DESTROY command instead.

For a description on how to enumerate the top level windows using the EnumWindows API, see my Enumerate all top level windows program. To check which windows are associated with the process we want to stop, the GetWindowThreadProcessId function is called. As its name implies this API returns the Process ID for a given window. If the PID matches that of the shelled application, the window handle is written to the collection.

In many situations you do not know the PID of the application to shut down because you didn't start it. By enumerating the windows you can compare their captions to that of the application to stop. Again, once you have the handle of the window with a matching caption you can use the GetWindowThreadProcessId function to get its PID. All of this is demonstrated in my enumerate top level windows sample.

Instructions

Download the source code and press F5 to run the program. Enter the full path of the application to start. Click the Start Process button to run the application. You can then minimize or hide the application. When you want to terminate it, simply click the End Process button.








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