[Lazarus] RFC: Selection Editors to extend handling of object inspector selections

[Sven Barth]

Am 10.11.2019 um 22:26 schrieb Sven Barth:
> Hello together!
>
> I've got a RFC for a feature that allows to extend the IDE. It's based 
> on something that Delphi supports as well: Selection Editors.
> Unlike Component Editors these are supposed to be used to interact 
> with a specific selection in the designer and (in Delphi) allow the 
> following extensions:
> - adding menu items for the context menu for the selection (like 
> component editors)
> - add additional units when the component is dropped onto the form 
> (though I wonder why that isn't part of component editors)
> - add or remove properties to/from the object inspector for the selection
>
> My current RFC only implements the last one and also a bit different 
> than Delphi does cause they added that functionality only later (see 
> below).
>
> Due to their dependencies Selection Editors live in the PropEdits unit 
> and like component and property editors they are registered at an 
> approbriate location (be it some Register function or a unit 
> initialization). When the object inspector requests the properties it 
> also checks all selection editors involved in the selection (included 
> the parent classes) and calls the selection editor's FilterProperties 
> method if GetAttributes contains seaFilterProperties (Delphi does not 
> provide a GetAttributes method, instead it provides FilterProperties 
> through an interface that needs to be implemented by a selection editor).
> FilterProperties receives both the current selection of the object 
> inspector as well as the list of property editors. It is then free to 
> add or remove property editors as it sees fit.
> The behavior when collecting the property editors is such that 
> multiple FilterProperties methods might be called on the same 
> selection, thus it might received an already filtered property editor 
> list.
>
> I've attached a patch that implements selection editors 
> (selection-editors.patch) as well as an example implementation for a 
> component that Lazarus already supports and Delphi provides a 
> selection editor for: TFlowPanel (tflowpanel-seledit.patch). For that 
> component for each child control a virtual ControlIndex property is 
> exposed which allows to easily change the order of the components in 
> the object inspector instead of going through some collection editor. 
> Also the Top and Left properties are removed as they aren't useful for 
> such components. Delphi behaves the same here.
>
> Another example use would be TGridPanel which we don't have yet: it 
> allows to implement the Row- and ColumnSpan properties on each child 
> control of the panel.
>
> To work correctly I also had to adjust the object inspector a little 
> bit (respect-parevertable.patch), cause it is not using only the 
> virtual functions provided by TPropertyEditor: namely to respect the 
> paRevertable attribute and only initialize and use the undo values if 
> the property is deemed revertable. For demonstration purposes I've 
> disabled the paRevertable attribute for the ControlIndex property 
> editor, cause otherwise there'd be an exception when the object 
> inspector tries to read the original value. It would be better if the 
> object inspector would only call virtual methods of TPropertyEditor 
> however or ones that can be easily faked (like I did by faking a 
> TPropInfo entry, though that does not feel really nice either).
>
> Suggestions and criticism are welcome though I can't tell how much 
> time I currently can and want to invest to improve this further. It 
> might also need some step-by-step improvement of the existing 
> TPropertyEditor interface to function smoothly.

Really? No further interest here? I don't want to put it on Mantis yet, 
because I'm not yet sure whether everything is alright and Mantis is not 
a discussion platform...

Regards,
Sven