Drag and drop misses some comments and tests

[tinchodias]

@Enzo-Demeulenaere asked about this topic in the mailing list, and I realized this is missing: We should write class comments in the hierarchy of drag and drop events.

The BlMouseProcessor>>#handleMouseMove: method is who takes into account whether the drag start was consumed and acts in consequence.

A simple example the shows a key sentence to handle drag and drop:

space := BlSpace new.
element :=
	BlElement new
		background: Color purple;
		yourself.
space root addChild: element.
space show.

element addEventHandler: (BlEventHandler
	on: BlDragStartEvent
	do: [ :evt |
		evt traceCr.
		evt consumed: true " <--- THIS IS KEY " ]).
element addEventHandler: (BlEventHandler
	on: BlDragEvent
	do: [ :evt | evt traceCr ]).
element addEventHandler: (BlEventHandler
	on: BlDragEndEvent
	do: [ :evt | evt traceCr ])

[tinchodias]

An example that uses drag&drop is: BlFlowLayoutCompositionSmokeTest floatingCells

Double click on a rectangle inserts a BlElementSelection, which is a class in the package 'Bloc-DevTool' that allows move and resize.

[Ducasse]

BTW we should check the status of Bloc-DevTool because may we should add some elements to Bloc by default.

[Ducasse]

Thinking about the example I asked myself

• what is the difference between BlDragEvent and BlBaseEvent
• why this is the responsibility of the user to mark the event as consumed. May be in case of reject of drag?
• why we do not have to mark the BlDragEvent as consumed then.

S

[tinchodias]

- what is the difference between BlDragEvent and BlBaseEvent BlDragEvent is similar to a "mouse move", it's dispatched many times along

the path of the cursor the base is the superclass with common API

- why this is the responsibility of the user to mark the event as consumed. May be in case of reject of drag? Yes it is that. Maybe it deserves to be a separate flag anyway, if we

think on what it represents. I mean, it may be better to add a "startDrag" flag to API that explicitely marks if the drag must start, because consume is not necesarily the same thing. Consuming the event is part of the event bubbling dispatcher. It is kind of this, in few words: the dispatcher iterates the tree of elements of the space asking "do you want this event"? when an element wants it, it marks a consumer:true, to the iteration stops.

…

- why we do not have to mark the BlDragEvent as consumed then. answered above Message ID: ***@***.***>

[tinchodias]

An example that uses drag&drop is: BlFlowLayoutCompositionSmokeTest floatingCells

Double click on a rectangle inserts a BlElementSelection, which is a class in the package 'Bloc-DevTool' that allows move and resize.

I should have sent a capture of the example:

Screen.Recording.2024-01-16.at.12.43.55.mov

[Ducasse]

It would be nice to check the halos developed by alain and decide which ones we keep but use them :)

[tinchodias]

Drag and Drop is being discussed in #649