[Lazarus] Generalized DragDrop

[Hans-Peter Diettrich]

Graeme Geldenhuys schrieb:

> That's the beauty of that design.... internal component-to-component
> or external app-to-app DND is handled exactly the same - from the
> developers perspective. That was the whole point of that
> implementation - so you application is single source, no matter the
> platform (and importantly, no IFDEF's).

Very nice, so far.

> Internally the fpGUI frame can
> optimize for internal component-to-component DND without needing to
> speak to the OS or window manager.

This is what may pollute the current design.

> I have also note that the fpGUI DND implementation is not 100%
> complete yet. Currently I still need to implement the non-text data
> transmission. Not hard to implement, because the internal workings are
> already implement in fpGUI. I just need to find some time, to complete
> the alternative data types handling.

I feel that there remains much more to do. It starts with the assignment 
and handling of the existing and possibly added mime types, adding 
process information (and more) to the drag info...


>>> - More drag and drop types should be defined, in addition to "drop" and
>>> "dock", e.g. "open files", "link" or "embed". Eventually specialized drag
>>> targets must register themselves, for e.g. accepting files or embedding
>>> objects, in addition do DockSite registration.
>> I'm all for it. Although I'm not sure that this can be implemented in a
>> cross-platform way.
> 
> I not sure if I understand the original statement, but in fpGUI I use
> the mime types to register the data that must be transfered via DND.
> Under Windows, I also register common mime-types that have easy
> mappings to Windows weird CF_xxx types. So if you register
> 'text/plain' data in fpGUI, then under Windows, it will also register
> CF_TEXT for example.

Clipboard formats (CF_...) may be usable on all platforms with a 
comparable/compatible clipboard functionality. But what about all the 
other platforms?


>> On Windows, the intra-app drag/drop is handled using OLE/DDE. On Linux,
>> there is no such thing, and I think it depends on the used desktop software
>> (KDE vs Gnome).
> 
> Correct, under Windows I use OLE DND, and under Linux I use the XDND
> protocol which uses mime-types. The XDND protocol has support for any
> data types that you can describe with mime.

Your current implementation is restricted to purely textual information, 
and I'm not sure whether your implementation of rich (html...) text will 
match the platform standards - with possibly different standards on 
every single platform :-(

Question remains: which mime type should be associated with e.g. 
dragging files, or forms?

How comes that I cannot drop anything from outside the demo app, and no 
other app accepts the "Drag Me!"?

DoDi