204 lines
6.5 KiB
C++
204 lines
6.5 KiB
C++
// -*- c++ -*-
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/* $Id: property.cc,v 1.3 2006/05/12 08:08:43 murrayc Exp $ */
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/* Copyright 2002 The gtkmm Development Team
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the Free
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* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <glibmm/property.h>
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#ifdef GLIBMM_PROPERTIES_ENABLED
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#include <glibmm/object.h>
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#include <cstddef>
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// Temporary hack till GLib gets fixed.
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#undef G_STRLOC
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#define G_STRLOC __FILE__ ":" G_STRINGIFY(__LINE__)
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namespace
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{
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// OK guys, please don't kill me for that. Let me explain what happens here.
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//
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// The task:
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// ---------
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// a) Autogenerate a property ID number for each custom property. This is an
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// unsigned integer, which doesn't have to be assigned continuously. I.e.,
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// it can be everything but 0.
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// b) If more than one object of the same class is instantiated, then of course
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// the already installed properties must be used. That means, a property ID
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// must not be associated with a single Glib::Property<> instance. Rather,
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// the ID has to be associated with the class somehow.
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// c) With only a GObject pointer and a property ID (and perhaps GParamSpec*
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// if necessary), it must be possible to acquire a reference to the property
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// wrapper instance.
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//
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// The current solution:
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// ---------------------
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// a) Assign an ID to a Glib::PropertyBase by calculating its offset in bytes
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// relative to the beginning of the object's memory. dynamic_cast<void*>
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// is used to retrieve a pointer to the very beginning of an instance.
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// b) Recalculate a specific PropertyBase pointer by adding the property ID
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// (i.e. the byte offset) to the object start pointer. The result is then
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// just casted to PropertyBase*.
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//
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// Drawbacks:
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// ----------
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// a) It's a low-level hack. Should be portable, yes, but we can only do very
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// limited error checking.
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// b) All Glib::Property<> instances are absolutely required to be direct data
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// members of the class that implements the property. That seems a natural
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// thing to do, but it's questionable whether it should be a requirement.
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//
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// Advantages:
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// -----------
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// a) Although low-level, it's extremely easy to implement. The nasty code is
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// concentrated in only two non-exposed utility functions, and it works
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// just fine.
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// b) It's efficient, and the memory footprint is very small too.
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// c) I actually tried other ways, too, but ran into dead-ends everywhere.
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// It's probably possible to implement this without calculating offsets,
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// but it'll be very complicated, and involve a lot of qdata pointers to
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// property tables andwhatnot.
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//
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// We can reimplement this later if necessary.
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static unsigned int property_to_id(Glib::ObjectBase& object, Glib::PropertyBase& property)
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{
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void *const base_ptr = dynamic_cast<void*>(&object);
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void *const prop_ptr = &property;
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const ptrdiff_t offset = static_cast<guint8*>(prop_ptr) - static_cast<guint8*>(base_ptr);
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g_return_val_if_fail(offset > 0 && offset < G_MAXINT, 0);
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return static_cast<unsigned int>(offset);
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}
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Glib::PropertyBase& property_from_id(Glib::ObjectBase& object, unsigned int property_id)
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{
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void *const base_ptr = dynamic_cast<void*>(&object);
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void *const prop_ptr = static_cast<guint8*>(base_ptr) + property_id;
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return *static_cast<Glib::PropertyBase*>(prop_ptr);
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}
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} // anonymous namespace
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namespace Glib
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{
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void custom_get_property_callback(GObject* object, unsigned int property_id,
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GValue* value, GParamSpec* param_spec)
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{
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if(Glib::ObjectBase *const wrapper = Glib::ObjectBase::_get_current_wrapper(object))
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{
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PropertyBase& property = property_from_id(*wrapper, property_id);
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if((property.object_ == wrapper) && (property.param_spec_ == param_spec))
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g_value_copy(property.value_.gobj(), value);
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else
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G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, param_spec);
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}
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}
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void custom_set_property_callback(GObject* object, unsigned int property_id,
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const GValue* value, GParamSpec* param_spec)
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{
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if(Glib::ObjectBase *const wrapper = Glib::ObjectBase::_get_current_wrapper(object))
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{
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PropertyBase& property = property_from_id(*wrapper, property_id);
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if((property.object_ == wrapper) && (property.param_spec_ == param_spec))
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{
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g_value_copy(value, property.value_.gobj());
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g_object_notify(object, g_param_spec_get_name(param_spec));
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}
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else
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G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, param_spec);
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}
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}
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/**** Glib::PropertyBase ***************************************************/
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PropertyBase::PropertyBase(Glib::Object& object, GType value_type)
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:
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object_ (&object),
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value_ (),
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param_spec_ (0)
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{
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value_.init(value_type);
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}
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PropertyBase::~PropertyBase()
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{
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if(param_spec_)
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g_param_spec_unref(param_spec_);
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}
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bool PropertyBase::lookup_property(const Glib::ustring& name)
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{
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g_assert(param_spec_ == 0);
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param_spec_ = g_object_class_find_property(G_OBJECT_GET_CLASS(object_->gobj()), name.c_str());
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if(param_spec_)
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{
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g_assert(G_PARAM_SPEC_VALUE_TYPE(param_spec_) == G_VALUE_TYPE(value_.gobj()));
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g_param_spec_ref(param_spec_);
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}
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return (param_spec_ != 0);
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}
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void PropertyBase::install_property(GParamSpec* param_spec)
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{
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g_return_if_fail(param_spec != 0);
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const unsigned int property_id = property_to_id(*object_, *this);
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g_object_class_install_property(G_OBJECT_GET_CLASS(object_->gobj()), property_id, param_spec);
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param_spec_ = param_spec;
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g_param_spec_ref(param_spec_);
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}
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const char* PropertyBase::get_name_internal() const
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{
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const char *const name = g_param_spec_get_name(param_spec_);
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g_return_val_if_fail(name != 0, "");
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return name;
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}
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Glib::ustring PropertyBase::get_name() const
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{
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return Glib::ustring(get_name_internal());
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}
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void PropertyBase::notify()
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{
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g_object_notify(object_->gobj(), g_param_spec_get_name(param_spec_));
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}
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} // namespace Glib
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#endif //GLIBMM_PROPERTIES_ENABLED
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