How do you set an enum property on a GLib object?

问题

I am trying to set the "ellipsize" enum property on a GtkCellRendererText object.

I am trying to use g_object_set_property as follows:

GtkCellRenderer *renderer = gtk_cell_renderer_text_new ();

GValue val = G_VALUE_INIT;
g_value_init (&val, G_TYPE_ENUM);
g_value_set_enum (&val, PANGO_ELLIPSIZE_END);
g_object_set_property (G_OBJECT(renderer), "ellipsize", &val);

However, I get an error message at run time:

(infog:27114): GLib-GObject-WARNING **: 12:24:29.848: ../../../../gobject/gvalue.c:188: cannot initialize GValue with type 'GEnum', this type is abstract with regards to GValue use, use a more specific (derived) type

How do I get the type ID for enum PangoEllipsizeMode that derives from G_TYPE_ENUM?

回答1:

You need to initialise the GValue container with the type of the enumeration that the property expects. G_TYPE_ENUM is the generic, abstract enumeration type.

The "ellipsize" property of GtkCellRendererText expects a PangoEllipsizeMode enumeration value, which has a GType of PANGO_TYPE_ELLIPSIZE_MODE.

GtkCellRenderer *renderer = gtk_cell_renderer_text_new ();

GValue val = G_VALUE_INIT;

g_value_init (&val, PANGO_TYPE_ELLIPSIZE_MODE);
g_value_set_enum (&val, PANGO_ELLIPSIZE_END);

g_object_set_property (G_OBJECT(renderer), "ellipsize", &val);

// Always unset your value to release any memory that may be associated with it
g_value_unset (&val);

回答2:

Using g_object_set instead works:

g_object_set (G_OBJECT(renderer), "ellipsize", PANGO_ELLIPSIZE_END, NULL);

来源：https://stackoverflow.com/questions/58540419/how-do-you-set-an-enum-property-on-a-glib-object