是否未释放COM对象未分配给var？

Question

如果我使用这样的代码，将释放所有非托管COM对象

var worksheet = new Application().Workbooks.Add().Worksheets.Add();
Marshal.ReleaseComObject(worksheet);

而不是像这样的代码

var excel = new Application();
var workbook = excel.Workbooks.Add();
var worksheet = workbook.Worksheets.Add();
Marshal.ReleaseComObject(excel);
Marshal.ReleaseComObject(workbook);
Marshal.ReleaseComObject(worksheet);

？

如果有一些文档，请发送回答链接。

Answer 1

实际上，两个代码示例都将在后台运行Excel进程。 例如，您需要在应用程序对象上调用Application.Quit() 。 以下作品：

private static void DoExcel()
    {
        var application = new Application();
        var workbook = application.Workbooks.Add();
        var worksheet = workbook.Worksheets.Add();

        // Name that this will be saved as
        string name = workbook.FullName + ".xlsx";

        string fullPath = Path.Combine(Directory.GetCurrentDirectory(), name);
        // If a file of the same name exists, delete it so that we won't be prompted if
        // we want to overwrite it when we save
        if (File.Exists(fullPath))
            File.Delete(fullPath);

        // Save the workbook - otherwise we may be prompted as to whether we want to save when we go to quit
        workbook.Save();

        // Quit the application
        application.Quit();

        // Release the references
        Marshal.ReleaseComObject(worksheet);
        Marshal.ReleaseComObject(workbook);
        Marshal.ReleaseComObject(application);

        // Release the .NET reference and run the garbage collector now to make sure the application is closed immediately
        worksheet = null;
        GC.Collect();
        GC.WaitForPendingFinalizers();
    }

还有一些值得记住的好东西：我没有在这里使用它，但是有一个Marshal.FinalReleaseComObject方法在这些情况下非常有用。 此外，我再次在我的代码示例中没有使用它，但Marshal.ReleaseComObject方法返回当前计数，因此如果您想确保计数达到零，您可以始终在循环中执行释放：

while (Marshal.ReleaseComObject(comObject) > 0) { }

您也可以将其用于调试目的 - 例如

int count = Marshal.ReleaseComObject(comObject);
Trace.TraceInformation("Current COM object reference count: " + count.ToString());