RE: [platform-ui-dev] Difference between Action and Command

["Scott Stanchfield" <scott@xxxxxxxxxxxx>]

One thing they did in Swing (that few people use, but it's actually quite
nice) is the concept of "Action Maps" and "Input Maps".

(Sorry if this is old news)

An "Action Map" is a mapping of an action object to a name; it's a unique id
for that action.

An "Input Map" is a mapping from an input control to the name of an action.

If used properly, this pair of maps allow easy end-user customization, while
at the same time allowing contexts to change the action map (the same input
map could be used against many action maps or vice versa).

So I'd like to see the binding of input controls to "action names", and a
context change the action map or input map as necessary. There would be a
single instance of each action, and the actions would do whatever is needed
(usually create and execute commands...)

-- Scott

> 
> -----Original Message-----
> From: platform-ui-dev-admin@xxxxxxxxxxx 
> [mailto:platform-ui-dev-admin@xxxxxxxxxxx] On Behalf Of Chris McLaren
> Sent: Wednesday, August 06, 2003 2:01 PM
> To: platform-ui-dev@xxxxxxxxxxx
> 
> The definitions are close. The term 'command', introduced in 
> 2.1 as part of the commands extension point, is used to 
> describe a request from a user. I define an 'action' as the 
> object which executes a command.
> 
> This distinction means:
> 
> 1. Commands have unique ids, names (used in menu labels, 
> etc), descriptions (used in tooltips), help ids.
> 2. Commands can have keybindings assigned to them.
> 3. Commands can be bound to particular contexts.
> 4. Commands can have various images bound to them (for use in 
> menus and
> toolbars)
> 5. Commands, via the context mechanism, decide whether or not 
> it should be visible in the menus or toolbars.
> 6. Actions do the actual work for a command. Based on the 
> active part, perspective, etc, the workbench chooses the best 
> action to which to delegate the actual execution of the command.
> 7. The action that the workbench has chosen decides whether 
> it is enabled or not ('can be executed'), and affects the 
> enabled state where commands appear on menus and toolbars.
> 8. The action can optionally override the name, description, 
> or help id to provide more specific information than the 
> command itself usually provides in those places in the UI 
> which accept these overrides, such as the menus and toolbars. 
> e.g. The current action for 'Copy' might override the name to 
> 'Copy Image', but should not override it to say 'Cut'. Other 
> parts of the UI would always use the proper name of the 
> command. e.g. the names and descriptions of the commands as 
> presented in the keybindings UI should not use any overridden 
> names or descriptions provided by the current actions, if any.
> 
> When I say 'command-centric' I'm thinking the following ideas:
> 
> 1. That perhaps menus and toolbars should be explicitly 
> defined in terms of commands. Rather than have the action 
> specify a menu or toolbar path, the command should be bound 
> to particular menus and toolbars, and the action should only 
> worry about handling command execution when it is asked. I am 
> currently exploring a 'menus' extension point to explicity 
> define reusable and compositable menus in terms of commands.
> 2. Keybindings and other means of command execution (i.e. 
> scripting..) should only be concerned with the command itself 
> and not the action.
> 
> As far any naming confusion with an undo/redo mechanism, I'm 
> not so concerned. Perhaps we will see that ideas are one in 
> the same when the time comes to add a proper undo/redo stack 
> to eclipse. The primary goal right now is to unwind some of 
> the more tangled knots in the current action architecture. I 
> am working on a 'Commands' proposal now, as well as perhaps 
> as separate proposal for a 'menus' extension point which 
> should help here.
> 
> Chris
> 
> 
> 
> 
> 
> 
> Randy Hudson/Raleigh/IBM@IBMUS
> Sent by: platform-ui-dev-admin@xxxxxxxxxxx
> 08/06/2003 01:21 PM
> Please respond to platform-ui-dev
> 
>  
>         To:     platform-ui-dev@xxxxxxxxxxx
>         cc: 
>         Subject:        [platform-ui-dev] Difference between 
> Action and Command
> 
> 
> 
> 
> In the recently announced "contexts" proposal: 
> "As Eclipse moves from an action-centric model to 
> command-centric model, 
> action sets would disappear entirely" 
> 
> To me "action" and "command" are the same thing.  What is the 
> difference 
> here between a command and an action?  Where can I read more 
> on the new 
> "command" stuff? 
> Won't this be confusing since the term "command" is widely 
> used to mean a 
> change which can be undone and redone?  There is also a bugzilla open 
> tracking the proposal to add undo/redo to the workbench. 
> 
> -Randy
> 
> 
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