Why Does My Excel Process Persist After Closing My C# Application, Even With a Release-Dispose-Collect-Wait Strategy?

Troubleshooting Persistent Excel Processes in C# Applications

You've implemented a robust release-dispose-collect-wait strategy to manage COM objects, yet your Excel process remains active after application closure. This points to lingering references to COM objects within your C# application.

A common culprit is implicitly referencing COM object members without explicit variable assignment. Consider the following example using the Worksheets object:

excelApp.Worksheets.Open(...);

This seemingly innocuous line creates a hidden reference to the Worksheets COM object, preventing Excel from releasing its resources.

The Solution: Explicit Variable Assignment and Release

The solution lies in explicit variable assignment and subsequent release of COM objects:

Worksheets sheets = excelApp.Worksheets;
Worksheet sheet = sheets.Open(...);

// ... your code ...

Marshal.ReleaseComObject(sheet);
Marshal.ReleaseComObject(sheets);

This approach grants you precise control over the object's lifecycle, enabling proper disposal.

Key Best Practice: Avoid Chained COM Object Access

Crucially, remember this rule when interacting with COM objects in C#: Avoid chaining member accesses using two dots. This means refraining from code like:

excelApp.Worksheets.Open(...);

Always opt for the explicit variable assignment method demonstrated above.

By adhering to these best practices, you'll effectively manage COM object lifetimes, ensuring the Excel process terminates cleanly upon application closure.

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