Custom Action


You are developing an explorable domain model of your application and find yourself repeatedly evaluating the same code snippets to perform a certain action or navigate to another object.


How can you streamline execution of repeated actions?


Repeated tasks are annoying and time-consuming.

Remembering how to perform common tasks increases cognitive overload.

Storing code to perform common actions as methods or as snippets in class comments doesn't guarantee that the code will be easily found when you need it.


Add a custom action button to the key objects involved in the repeated tasks, encapsulating the boilerplate code to perfom them.

Be sure to pick an evocative button icon and tooltip text to make the intent of the button clear. Only add buttons for the most important actions to avoid cluttering the interface of a moldable tool.


Consider GT slideshows. These are classes containing methods that use the <gtSlide> pragma. Here is a list of all such classes in this image:

(#gtSlide gtPragmas contents collect: #methodClass) asSet

The way to play a slideshow in a new window, for example, the GtTour Object subclass: #GtTour uses: TGtSlideShow instanceVariableNames: '' classVariableNames: '' package: 'GToolkit-Demo-MoldableDevelopment-Slideshows' slideshow, is to evaluate a snippet like this:

GtPresenterSlideShow openInSpace: GtTour

Sometime this information is stored in a class comment, as is the case for GtTour Object subclass: #GtTour uses: TGtSlideShow instanceVariableNames: '' classVariableNames: '' package: 'GToolkit-Demo-MoldableDevelopment-Slideshows' , or in cases where the slideshows inherit from a common class, it can be encapsulated in a class-side method, such as PrioritySlideshow>>#show show "NB: this is a class-side method." GtPresenterSlideShow openInSpace: self , but in any case, extra steps have to be performed to play the slideshow.

A solution is to add a custom <gtAction> button which will be displayed when you inspect the class. Here we see custom gtAction buttons to Inspect and to Play the GtPharo101 Object subclass: #GtPharo101 uses: TGtSlideShow instanceVariableNames: '' classVariableNames: '' package: 'GToolkit-Demo-Pharo101' slideshow.

Since most slideshow classes typically do share a common slideshow hierarchy, these actions are implemented in a trait TGtSlideShow Trait named: #TGtSlideShow instanceVariableNames: '' package: 'GToolkit-Presenter-Models - Support' , which can then used by all slideshow classes.

The implementation is straightforward in this case GtPharo101>>#gtOpenSlideshowActionFor: gtOpenSlideshowActionFor: anAction <gtAction> <gtClassAction> (self methods select: [ :m | m hasPragmaNamed: #gtSlide ]) isEmpty ifTrue: [ ^ anAction noAction ]. ^ anAction button priority: 11; tooltip: 'Play slideshow in new window'; icon: BrGlamorousVectorIcons play; action: [ :aButton | GtPresenterSlideShow openInSpace: self ]

In addition to the <gtAction> pragmas, there is also a <gtClassAction> pragma, so the button will also appear in a Coder.

The first line of the method checks that the class actually has a <gtSlide> method, otherwise the button will be suppressed (noAction). Then a button is displayed with a priority (the order in which buttons appear), a tooltip to display, an dicon and the action to perform.

Another typical example is the Open page in a new world tab button at the top of this page. You can Secondary-click on the button to see its implementation in LePage>>#gtOpenInNewTabActionFor: gtOpenInNewTabActionFor: anAction <lePageAction> ^ anAction button id: LeOpenPageInNewWorldTabElementId; tooltip: 'Open page in a new world tab'; icon: BrGlamorousVectorIcons spawn; action: [ :aButton | GtWorldUtility showSpaceWithTitle: self title inPagerWith: [ self asLepiterPagePhlowTool asElementDo: [ :e | e ] ] asStencil from: aButton ] . It streamlines the task of opening a new window for the current Lepiter notebook page, for example, by copying the page title, pasting it into Spotter, and then opening the found page.


Custom actions appear as buttons in moldable tools only in the context of the objects to which they can be applied.

You need a Moldable Tool into which you can dynamically plug custom actions.

Related patterns

A Custom View has a similar intent, but is more suitable when the goal is to quickly access information in an Inspector view that would otherwise be found only be one or more navigation steps.