Add GtkLayoutChild

Layout managers needs a way to store properties that control the layout
policy of a widget; typically, we used to store these in GtkContainer's
child properties, but since GtkLayoutManager is decoupled from the
actual container widget, we need a separate storage. Additionally, child
properties have their own downsides, like requiring a separate, global
GParamSpecPool storage, and additional lookup API.

GtkLayoutChild is a simple GObject class, which means you can introspect
and document it as you would any other type.

1 files changed, 77 insertions, 0 deletions

diff --git a/gtk/gtklayoutmanager.c b/gtk/gtklayoutmanager.c
index 7a5f2f08d5..02abe0d5c7 100644
--- a/gtk/gtklayoutmanager.c
+++ b/gtk/gtklayoutmanager.c
@@ -38,6 +38,7 @@
 #include "config.h"
 
 #include "gtklayoutmanagerprivate.h"
+#include "gtklayoutchild.h"
 #include "gtkwidget.h"
 
 #ifdef G_ENABLE_DEBUG
@@ -57,6 +58,8 @@ typedef struct {
 
 G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE (GtkLayoutManager, gtk_layout_manager, G_TYPE_OBJECT)
 
+static GQuark quark_layout_child;
+
 static GtkSizeRequestMode
 gtk_layout_manager_real_get_request_mode (GtkLayoutManager *manager,
                                           GtkWidget        *widget)
@@ -107,6 +110,8 @@ gtk_layout_manager_class_init (GtkLayoutManagerClass *klass)
   klass->get_request_mode = gtk_layout_manager_real_get_request_mode;
   klass->measure = gtk_layout_manager_real_measure;
   klass->allocate = gtk_layout_manager_real_allocate;
+
+  quark_layout_child = g_quark_from_static_string ("-GtkLayoutManager-layout-child");
 }
 
 static void
@@ -278,3 +283,75 @@ gtk_layout_manager_layout_changed (GtkLayoutManager *manager)
   if (priv->widget != NULL)
     gtk_widget_queue_resize (priv->widget);
 }
+
+/**
+ * gtk_layout_manager_get_layout_child:
+ * @manager: a #GtkLayoutManager
+ * @widget: a #GtkWidget
+ *
+ * Retrieves a #GtkLayoutChild instance for the #GtkLayoutManager, creating
+ * one if necessary
+ *
+ * The #GtkLayoutChild instance is owned by the #GtkLayoutManager, and is
+ * guaranteed to exist as long as @widget is a child of the #GtkWidget using
+ * the given #GtkLayoutManager.
+ *
+ * Returns: (transfer none): a #GtkLayoutChild
+ */
+GtkLayoutChild *
+gtk_layout_manager_get_layout_child (GtkLayoutManager *manager,
+                                     GtkWidget        *widget)
+{
+  GtkLayoutManagerPrivate *priv = gtk_layout_manager_get_instance_private (manager);
+  GtkLayoutChild *res;
+  GtkWidget *parent;
+
+  g_return_val_if_fail (GTK_IS_LAYOUT_MANAGER (manager), NULL);
+  g_return_val_if_fail (GTK_IS_WIDGET (widget), NULL);
+
+  parent = gtk_widget_get_parent (widget);
+  g_return_val_if_fail (parent != NULL, NULL);
+
+  if (priv->widget != parent)
+    {
+      g_critical ("The parent %s %p of the widget %s %p does not "
+                  "use the given layout manager of type %s %p",
+                  gtk_widget_get_name (parent), parent,
+                  gtk_widget_get_name (widget), widget,
+                  G_OBJECT_TYPE_NAME (manager), manager);
+      return NULL;
+    }
+
+  if (GTK_LAYOUT_MANAGER_GET_CLASS (manager)->create_layout_child == NULL)
+    {
+      g_critical ("The layout manager of type %s %p does not create "
+                  "GtkLayoutChild instances",
+                  G_OBJECT_TYPE_NAME (manager), manager);
+      return NULL;
+    }
+
+  /* We store the LayoutChild into the Widget, so that the LayoutChild
+   * instance goes away once the Widget goes away
+   */
+  res = g_object_get_qdata (G_OBJECT (widget), quark_layout_child);
+  if (res != NULL)
+    {
+      /* If the LayoutChild instance is stale, and refers to another
+       * layout manager, then we simply ask the LayoutManager to
+       * replace it, as it means the layout manager for the parent
+       * widget was replaced
+       */
+      if (gtk_layout_child_get_layout_manager (res) == manager)
+        return res;
+    }
+
+  res = GTK_LAYOUT_MANAGER_GET_CLASS (manager)->create_layout_child (manager, widget);
+  g_assert (res != NULL);
+  g_assert (g_type_is_a (G_OBJECT_TYPE (res), GTK_TYPE_LAYOUT_CHILD));
+
+  g_object_set_qdata_full (G_OBJECT (widget), quark_layout_child,
+                           res,
+                           g_object_unref);
+
+  return res;
+}