[rygel] tracker: Allow subclasses to fail on title/ID creation

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 2a7a35150181691a4b1f0c5de13d837f467d9f99
Author: Zeeshan Ali (Khattak) <zeeshanak gnome org>
Date:   Wed Dec 8 18:11:13 2010 +0200

    tracker: Allow subclasses to fail on title/ID creation
    
    Allow create_id_for_title and create_title_for_value virtual methods of
    MetadataValues to return null. When these methods return null for a
    metadata value, we simply ignore that value.

 .../tracker/rygel-tracker-metadata-values.vala     |   10 +++++++---
 src/plugins/tracker/rygel-tracker-years.vala       |    2 +-
 2 files changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/src/plugins/tracker/rygel-tracker-metadata-values.vala b/src/plugins/tracker/rygel-tracker-metadata-values.vala
index ee08061..472b946 100644
--- a/src/plugins/tracker/rygel-tracker-metadata-values.vala
+++ b/src/plugins/tracker/rygel-tracker-metadata-values.vala
@@ -125,8 +125,12 @@ public abstract class Rygel.Tracker.MetadataValues : Rygel.SimpleContainer {
             }
 
             var title = this.create_title_for_value (value);
+            if (title == null) {
+                continue;
+            }
+
             var id = this.create_id_for_title (title);
-            if (!this.is_child_id_unique (id)) {
+            if (id == null || !this.is_child_id_unique (id)) {
                 continue;
             }
 
@@ -165,11 +169,11 @@ public abstract class Rygel.Tracker.MetadataValues : Rygel.SimpleContainer {
         }
     }
 
-    protected virtual string create_id_for_title (string title) {
+    protected virtual string? create_id_for_title (string title) {
         return this.id + ":" + Uri.escape_string (title, "", true);
     }
 
-    protected virtual string create_title_for_value (string value) {
+    protected virtual string? create_title_for_value (string value) {
         return value;
     }
 
diff --git a/src/plugins/tracker/rygel-tracker-years.vala b/src/plugins/tracker/rygel-tracker-years.vala
index d9ef9f5..60173b3 100644
--- a/src/plugins/tracker/rygel-tracker-years.vala
+++ b/src/plugins/tracker/rygel-tracker-years.vala
@@ -37,7 +37,7 @@ public class Rygel.Tracker.Years : MetadataValues {
               KEY_CHAIN);
     }
 
-    protected override string create_title_for_value (string value) {
+    protected override string? create_title_for_value (string value) {
         return value.ndup (4);
     }