Re: new Target API [was: Re: introspection and broken API]

[James Henstridge <james jamesh id au>]

Ryan McDougall wrote:

> I noticed the new API in devhelp, but not how to use it. I mostly went
> by tests/testdnd.c.
>  
The tests/ subdirectory is not the best place to look for examples.  The 
files found there are often designed to stress test parts of GTK, or try 
and expose a particular bug.  They shouldn't be considered "best 
practices" for using GTK -- demos/gtk-demo is a better place to look, 
but doesn't seem to have a good example for this.

> How do you tell a widget to use a GtkTargetList? Create an empty
> GtkTargetEntry, call gtk_drag_dest_set with empty entry array, then call
> gtk_drag_dest_set_target_list?
>  
A GtkTargetList is used to represent the list of formats that a widget 
can provide for a drag, or accept for a drop.  If you are just using the 
simple APIs like gtk_drag_source_set() and gtk_drag_dest_set(), you just 
pass in an array of GtkTargetEntry's, which get converted into a target 
list.

The gtk_drag_{dest,source}_add_XXXX_targets() functions similarly let 
you ignore GtkTargetLists, so you may as well suggest their use in your 
tutorial.  Just call them after the corresponding 
gtk_drag_{dest,source}_set() call.  The "info" argument will be passed 
to your "drag_data_get" or "drag_data_received" handlers (it looks like 
you are calling this "target_type" in your tutorial).

In your "drag_data_get" or "drag_data_received" handlers, you can use 
the appropriate gtk_selection_data_* function to set or get the 
text/image/URI in the GtkSelectionData object.  Any necessary 
conversions will be taken care of for you.

> I'll add the new stuff to my tutorial ASAP.
>
> Also, I tried passing an gint32 in my tutorial since that was the
> simplest datatype not included in your new API. Is there a reason you
> can't pass integers?
>  
You can pass any kind of data via DnD -- you just need to make sure the 
sender and receiver agree on a name for that format.  I don't know if 
there is a commonly used format name for a 32-bit integer.

Do you have a particular use case in mind?  Possibly passing the integer 
as a string would be a good idea (you might want to advertise it as such 
whatever you do, so that you can drag to apps that can accept text drags).

Another note about your example: the way you pass an integer in the 
selection is not 64-bit clean.  When using format==32, you are expected 
to pass in an array of long's.  On 32-bit systems this is fine, since 
gint32 is the same size as long.  But on most 64-bit systems they are 
different, which will cause troubles (yes, this API is a bit weird, but 
it is weird in the same way as Xlib).  So your code should probably look 
like this:

const long integer_data = 42;
gtk_selection_data_set(selection_data, selection_data->target, 32, 
&integer_data, sizeof(integer_data));

Good luck,

James.