Re: custom TreeModel

[muppet <scott asofyet org>]

On Aug 21, 2005, at 7:44 AM, Jens Luedicke wrote:

> I whipped up a custom TreeModel and I get the following error:
>
> type Filer::ListStore does not support property 'Glib::Object' at
> /home/jens/devel/filer/Filer/FilePane.pm line 100.
>
> My custom TreeModel has 7 columns:
>
> $treemodel{ident $self} = new Filer::ListStore(qw(Glib::Object
> Glib::String Glib::String Glib::String Glib::String Glib::String
> Glib::Scalar));
>
> any idea how to fix this?

Short answer:

Either

  # set the column types in instance initializer.  handy for
  # future derivation, but not so handy if you wanted the
  # column types to be set by a subclass.
  sub INIT_INSTANCE {
      my $self = shift;
      # where set_column_types is a method of your own that
      # tells your instance what the column types are.  it doesn't
      # have to be like this, it could just be an array assignment.
      $self->set_column_types (qw(Glib::Object Glib::String...));
  }

or

  # parameterized constructor.
  sub new {
      my ($class, @column_types) = @_;
      my $self = Glib::Object::new ($type);
      # see note above about set_column_types
      $self->set_column_types (@_);
      return $self;
  }


Long answer:

You're inheriting Glib::Object::new(), which treats the argument list  
as property-name/value pairs.  However, you're trying to call it like  
Gtk2::ListStore::new, which takes a list of column types that are  
then passed to gtk_list_store_set_column_types().

The TreeModel GInterface provides an API for querying and using a  
TreeModel; each implementation is responsible for coming up with its  
own way to configure and populate the store.

Glib::Object::Subclass checks to see if your class has a new(); if it  
doesn't, it will alias YourClass::new() to Glib::Object::new(), which  
is a factory constructor.  This is important, because the factory  
constructor is the only way to create a GObject instance; the various  
widget and object constructors in each class of gtk+'s API are  
actually convenience functions which merely marshal their parameters  
into g_object_new().  To ensure useful derivation, pretty much  
everything that you can configure about a GObject should be made an  
object property, and no setup code should occur in a new()  
implementation.

For your Filer::ListStore, the first question is, "is this supposed  
to be a special-case store object, or a parameterized store?"  That  
is, will you want to create a Filer::ListStore with different column  
types in different parts of your code?  If the answer is "no", then  
set up your column types in INIT_INSTANCE so that no matter how the  
object gets created, the column types will be right.  If the answer  
is "yes", you'll need to provide some way to set the column types  
after the object has been instantiated.  Gtk2::ListStore provides  
set_column_types() for exactly this purpose.

You can, of course, mix and match these approaches.  For example,  
Filer::ListStore may be a parameterized list, but Filer::FooList may  
set the column types in its INIT_INSTANCE so that creating one is as  
simple as "$foolist = Filer::FooList->new($where_to_find_the_foos);".


--
muppet <scott at asofyet dot org>