Command Pattern Issues

[Tobin Harris]

Hi there,

I want to be able to chain up steps in a process into various
configurations. One approach I considered was the command pattern, where I
see this as a variation on the 'Macro' theme. An example of one such 'macro'
or process configuration is :

fileName = "c:\temp.txt";
CompositeCommand c = new CompositeCommand();
c.AddCommand( new ExtractFileData( fileName, "output.dat" ) );
c.AddCommand( new FtpFile( ftpSettings, fileName )
c.AddCommand( new ZipUpFile( fileName, fileName + ".zip" ) );
c.AddCommand( new MoveFile( fileName + ".zip", "c:\backup\" + ) );
c.Run();

Another configuration might include some steps, exclude others etc.

Anyone ever done this kinda thing? My main consideration is that I don't
have any flow control, for example, for aborting the macro on failure etc?
Perhaps the commands interface be something like the following so I can test
for success before going to the next step?

interface Command{
void Run();
bool Succeeded();
}

Any thoughts or experiences on this would be apprecitaed before I get
carried away down a fruitless route!?

Tobes

[Mikkel Heisterberg]

I have used a similar approach to implement a very similar scenario
(text editing using a particular third party API). In my approach the
"run" method throws an exception on failure, and since all must complete
or none I can abort if an exception is caught.

Your example looks to be similar.

I have had a lot of benefit from structuring the code using the Command
pattern on a number of occasions.

lekkim

Tobin Harris wrote:
> Hi there,
>
> I want to be able to chain up steps in a process into various
> configurations. One approach I considered was the command pattern, where I
> see this as a variation on the 'Macro' theme. An example of one such 'macro'
> or process configuration is :
>
> fileName = "c:\temp.txt";
> CompositeCommand c = new CompositeCommand();
> c.AddCommand( new ExtractFileData( fileName, "output.dat" ) );
> c.AddCommand( new FtpFile( ftpSettings, fileName )
> c.AddCommand( new ZipUpFile( fileName, fileName + ".zip" ) );
> c.AddCommand( new MoveFile( fileName + ".zip", "c:\backup\" + ) );
> c.Run();
>
> Another configuration might include some steps, exclude others etc.
>
> Anyone ever done this kinda thing? My main consideration is that I don't
> have any flow control, for example, for aborting the macro on failure etc?
> Perhaps the commands interface be something like the following so I can test
> for success before going to the next step?
>
> interface Command{
> void Run();
> bool Succeeded();
> }
>
> Any thoughts or experiences on this would be apprecitaed before I get
> carried away down a fruitless route!?
>
> Tobes
>
>

[Richard Wheeldon]

Tobin Harris wrote:
> I want to be able to chain up steps in a process into various
> configurations. One approach I considered was the command pattern, where I
> see this as a variation on the 'Macro' theme. An example of one such 'macro'
> or process configuration is :
>
> fileName = "c:\temp.txt";
> CompositeCommand c = new CompositeCommand();
> c.AddCommand( new ExtractFileData( fileName, "output.dat" ) );
> c.AddCommand( new FtpFile( ftpSettings, fileName )
> c.AddCommand( new ZipUpFile( fileName, fileName + ".zip" ) );
> c.AddCommand( new MoveFile( fileName + ".zip", "c:\backup\" + ) );
> c.Run();
....
> Any thoughts or experiences on this would be apprecitaed before I get
> carried away down a fruitless route!?

Not really a pattern advice, but have you considered writing the code
as a set of Ant tasks ? In the above example, that would mean you'd
probably have to write code for a ExtractFileData task (hopefully
using a better name!). The ftp, zip and move commands are already
written, you'd just have to write the xml to configure it.

Richard

[Tobin Harris]

"Richard Wheeldon" <richard@rswheeldon.com> wrote in message
news:3F00A524.2781@rswheeldon.com...
> Tobin Harris wrote:
> > Any thoughts or experiences on this would be apprecitaed before I get
> > carried away down a fruitless route!?
>
> Not really a pattern advice, but have you considered writing the code
> as a set of Ant tasks ? In the above example, that would mean you'd
> probably have to write code for a ExtractFileData task (hopefully
> using a better name!). The ftp, zip and move commands are already
> written, you'd just have to write the xml to configure it.

An interesting idea actually! For this project it probably wouldn't be
suitable, becuase it has a GUI and I need threading control etc (I'm sure it
could be done, but perhaps a little too much research). Something similar to
the ANT configuration file is a nice way of building 'Jobs' though.

Regards,

Tobin

> Richard