Re: Equivalent to gtk_drag_get_source_widget()?

[Matthias Kaeppler <matthias finitestate org>]

Chris Vine wrote:
> The drag_data_received signal in GTK+ will pass the target widget as its first 
> paramater.  The gtkmm equivalent does not, but there is a good reason for 
> that, namely that the receiving object knows what it is.  The 
> Gtk::Widget::on_drag_data_received() method will be called on the object 
> which received the drag.

True.

> You should not really need to know either what object the data was dragged 
> from either.

I do, because I need some form of this check:

if (source == target)
   don't do anything;
else
   issue some operation

This is to prevent the user from issueing an operation on the same 
widget when it's only allowed from one widget to another.

My solution right now is to do as follows:
I have a member variable (an enum type) in my window class which 
identifies the source widget of the last drag. To the drag_begin signal 
which is always fired by the source widget I bind a value of this enum 
typ which identifies the source widget. When the signal handler is 
entered, I assign the member variable this value.
I also bind such a value to a signal which is fired by the receiving 
widget, and can thereby check in its signal handler if this value equal 
the value which was stored in the member variable after the last drag.

> First, it may not be in the same address space as the process
> receiving the drag (gtk_drag_get_source_widget() will return NULL in that 
> case, and where it is in the same address space you can store it in a 
> variable assessible to both widgets if you really need it).  Secondly, if you 
> want to notify the source object that the drag has been completed there are 
> signals available for that, via gtk_drag_finish() (or the gtkmm equivalent).

Now that you name it, my "solution" might actually not work when someone 
drags something from another application into mine. I will have to look 
into that further.

Best regards,
Matthias Kaeppler