Command Line Arguments

Command line arguments can be either options or file names. If an argument is a file name, the file will be opened as assembly and added to the current assembly list.

Available options:

/singleInstance    If ILSpy is already running, activates the existing instance
                   and passes command line arguments to that instance.
                   This is the default value if /list is not used.

/separate          Start up a separate ILSpy instance even if it is already running.

/noActivate        Do not activate the existing ILSpy instance. This option has no effect
                   if a new ILSpy instance is being started.

/list:listname     Specifies the name of the assembly list that is loaded initially.
                   When this option is not specified, ILSpy loads the previously opened list.
                   Specify "/list" (without value) to open the default list.
                   
                   When this option is used, ILSpy will activate an existing instance
                   only if it uses the same list as specified.
                   
                   [Note: Assembly Lists are not yet implemented]

/clearList         Clears the assembly list before loading the specified assemblies.
                   [Note: Assembly Lists are not yet implemented]

/navigateTo:tag    Navigates to the member specified by the given ID string.
                   The member is searched for only in the assemblies specified on the command line.
                   Example: 'ILSpy ILSpy.exe /navigateTo:T:ICSharpCode.ILSpy.CommandLineArguments'
                   
                   The syntax of ID strings is described in appendix A of the C# language specification.

/language:name     Selects the specified language.
                   Example: 'ILSpy /language:C#' or 'ILSpy /language:IL'

WM_COPYDATA (SendMessage API):

ILSpy can be controlled by other programs that send a WM_COPYDATA message to its main window. The message data must be an Unicode (UTF-16) string starting with "ILSpy:\r\n". All lines except the first ("ILSpy:") in that string are handled as command-line arguments. There must be exactly one argument per line.

That is, by sending this message:

ILSpy:
C:\Assembly.dll
/navigateTo:T:Type

The target ILSpy instance will open C:\Assembly.dll and navigate to the specified type.

ILSpy will return TRUE (1) if it handles the message, and FALSE (0) otherwise. The /separate option will be ignored; WM_COPYDATA will never start up a new instance. The /noActivate option has no effect, sending WM_COPYDATA will never activate the window. Instead, the calling process should use SetForegroundWindow(). If you use /list with WM_COPYDATA, you need to specify /singleInstance as well, otherwise ILSpy will not handle the message if it has opened a different assembly list.