Re: FW: [gtkmm] drag and drop with multiple targets

[pks timing com]

I messed up replying to the mailing list ... here it is

Callum Prentice writes:
 >
 > in the example i have, the data is set in the event handler method using
 > gtk_selection_data_set () but all widgets trigger the same method and (as far as i can tell)
 > there is nothing passed in that allows me to differentiate between widgets.

that's were subclassing your widget and overriding the virtual functions
that correspond to the signal_drag_data_get() and signal_drag_data_received()
signals, that is on_drag_data_get() and on_drag_data_received() comes in ...

in on_drag_data_get() the this pointer will be the source widget,
and in on_drag_data_received() the this pointer will be target widget ...

if subclassing the widget you will have hundreds of still doesn't sound
appealing, and

 > need to know which widget was dropped onto 

is the only thing standing in your way, just bind the destination widget
using the signal system using SigC::bind().  Here is a really simple
example using signal_show() and signal_hide():

//-----------------------------------------------------------------------

#include <gtkmm.h>
#include <iostream>

using namespace std;

class Example : public Gtk::Window
{
public:

    Example();

    Gtk::VBox _vbox;
    Gtk::Label *_lbls[5];

    // neither the show signal, nor the hide signal usually
    // provide any params ... but we'll bind a label (per
    // signal handler connection) to the show signal

    void OnLabelHide();
    void OnLabelShow(Gtk::Label *lbl);
};

Example::Example()
    : Gtk::Window(),
      _vbox(false, 5)
{
    for (int i = 0; i < 5; i++)
    {
	_lbls[i] = new Gtk::Label("foo");
	_vbox.pack_start(*_lbls[i], false, false);
	cout << "_lbls[" << i << "] = " << _lbls[i] << endl;

	// attach the hide signal handler as always
	_lbls[i]->signal_hide().connect(
	    SigC::slot(*this, &Example::OnLabelHide));

	// as we attach the signal handler, we bind the label's
	// address to the connection
	_lbls[i]->signal_show().connect(
	    SigC::bind(SigC::slot(*this, &Example::OnLabelShow), _lbls[i]));
    }

    cout << endl;
    add(_vbox);
    show_all();
}

void
Example::OnLabelShow(Gtk::Label *lbl)
{
    cout << "label " << lbl << " is being shown" << endl;
}

void
Example::OnLabelHide()
{
    cout << "\tsome label is being hidden" << endl;
}

int
main(int argc, char *argv[])
{
    Gtk::Main kit(argc, argv);
    Example example;
    kit.run(example);
    return 0;
}

//--------------------------------------------------------------------

you can bind the destination widget address to the drag drop signals
in the same way:

*) make the parameter to be bound the last one in the signature
*) SigC::bind the parameters value

or subclass, and have the "this" pointer at your disposal ;)

hope this helps