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ID: 20735, How to prevent multiple application instances?

by Sergey Kryukov Email: Anonymous

There are many solutions published. This is the only complete one, as far as I know.
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For C#Builder, Version 1.0  to 1.0 625 downloads
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Updated on Tue, 07 Oct 2003 09:09:40 GMT
Originally uploaded on Tue, 07 Oct 2003 09:03:32 GMT
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There are many solutions published. This is the only complete one, as far as I know.

One should take into account the following: processes can be found by its executable file name, without path and extension, but for comparison of the current and previous instance must involve full path. From the other hand, comparison of the current instance with all the available processes would be more costly. Finally, to exclude the current process from the search it Id can be used.

Quite another problem is to bring the previous instance to front if the application is windowed. Just making the main window found in the previous instance a foreground one would not always work because of modal forms or dialog possibly running. See my solution for more detail.


See the cSingletonApp class (SingletonApp.cs).

cSingletonApp.PreviousInstanceDetected detects previous instance of the application and returns its MainWindowHandle (if any).

cSingletonApp.ShowPreviousInstance is more tricky. If the MainWindowHandle of the previous application instance is available, it activates the main window. What makes it tricky is that it works correctly even if some modal form is active or some dialog is running.

How to build demo?

See demo application DemoApplication.cs. The calls to the cSingletonApp methods are shown in the region "Demo code".

You only need the .NET framework installed. Assuming there is a framework's bin directory in your PATH, 1) run build.bat, 2) or run make or nmake in the directory where the makefile is located.

-- Sergey A. Kryukov

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