Get object constructor arguments

Platform
1

how can i get the arguments passed when creating an object?
I tried this but I get errors:
foo.h

#ifndef FOO_H
#define FOO_H

#include <glib-object.h>

G_BEGIN_DECLS

#define E_TYPE_FOO e_foo_get_type()
G_DECLARE_DERIVABLE_TYPE (EFoo, e_foo, E, FOO, GObject)

struct _EFooClass{
    GObjectClass parent_class;
};

EFoo* e_foo_new(int a);

G_END_DECLS

#endif //FOO_H

foo.c

#include <stdio.h>
#include "foo.h"

G_DEFINE_TYPE (EFoo, e_foo, G_TYPE_OBJECT)

static void e_foo_class_init(EFooClass* self){
}

static void e_foo_init(EFoo* self)
{
		int a;
		g_object_get(self, "a", &a, NULL);
    printf("%d\n",a);
}

EFoo* e_foo_new(int a){
    return g_object_new(E_TYPE_FOO,"a",a, NULL);
}

errors:

(process:2010015): GLib-GObject-CRITICAL **: 22:29:31.151: g_object_new_is_valid_property: object class ‘EFoo’ has no property named ‘a’
(process:2010015): GLib-GObject-WARNING **: 22:29:31.153: g_object_get_is_valid_property: object class ‘EFoo’ has no property named ‘a’

how to get arguments correctly?

2

You need to add properties to the object: GObject – 2.0: Type System Concepts

1 Like
3

i changed the code and it partly works but i get 0 in e_foo_init and only then 10 is assigned. can i get the argument value in e_foo_init function?

#include <stdio.h>
#include "foo.h"

struct _EFooPrivate
{
	int a;
};

G_DEFINE_TYPE_WITH_PRIVATE (EFoo, e_foo, G_TYPE_OBJECT)

typedef enum
{
  A = 1,
  N_PROPERTIES
} Property;

static GParamSpec *obj_properties[N_PROPERTIES] = { NULL, };

static void e_foo_set_property (GObject      *object,
                          guint         property_id,
                          const GValue *value,
                          GParamSpec   *pspec)
{
  EFoo* self = E_FOO(object);

  switch ((Property) property_id)
    {
    case A:
			int a = g_value_get_int (value);
			printf("%d\n", a);

			  EFooPrivate *priv;

  			priv = e_foo_get_instance_private (E_FOO(object));

				priv->a = a;
      break;
    default:
      /* We don't have any other property... */
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
      break;
    }
}

static void e_foo_get_property (GObject    *object,
                          guint       property_id,
                          GValue     *value,
                          GParamSpec *pspec)
{
  EFoo *self = E_FOO (object);

  switch ((Property) property_id)
    {
    case A:
			
			  EFooPrivate *priv;

  			priv = e_foo_get_instance_private (E_FOO(object));

      g_value_set_int (value, priv->a);
      break;

    default:
      /* We don't have any other property... */
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
      break;
    }
}


static void e_foo_class_init(EFooClass* self){
	GObjectClass *object_class = G_OBJECT_CLASS (self);

	object_class->set_property = e_foo_set_property;
  object_class->get_property = e_foo_get_property;

	obj_properties[A] =
    g_param_spec_int ("a",
                         "a",
                         "the a",
												 -100,
												 100,
                         0  /* default value */,
                         G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE);
	g_object_class_install_properties (object_class,
                                     N_PROPERTIES,
                                     obj_properties);	
}

static void e_foo_init(EFoo* self)
{
		int a;
		g_object_get(self, "a", &a, NULL);
    printf("new %d\n",a);
}

EFoo* e_foo_new(int a){
    return g_object_new(E_TYPE_FOO,"a",a, NULL);
}

when an object is created, it prints:

new 0
10

main.c

#include "foo.h"

int main() {
    EFoo* foo = e_foo_new(10);
    return 0;
}
4

No. The instance initialization is used precisely for that: instance initialization. Properties are applied after that.

If you have a constructor property, you want to override GObjectClass.constructed; at at point, the value of constructor and constructor-only properties will be set.

I strongly encourage you to read the GObject documentation.

1 Like
5

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