Fix a memory leak in Tile.Image when using AlphaHack. r=crschmidt (closes #1848)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@8407 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Tile/Image.js

@@ -109,10 +109,14 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
     destroy: function() {
         if (this.imgDiv != null)  {
             if (this.layerAlphaHack) {
+                // unregister the "load" handler
                 OpenLayers.Event.stopObservingElement(this.imgDiv.childNodes[0].id);                
-            } else {
-                OpenLayers.Event.stopObservingElement(this.imgDiv.id);
             }
+
+            // unregister the "load" and "error" handlers. Only the "error" handler if
+            // this.layerAlphaHack is true.
+            OpenLayers.Event.stopObservingElement(this.imgDiv.id);
+            
             if (this.imgDiv.parentNode == this.frame) {
                 this.frame.removeChild(this.imgDiv);
                 this.imgDiv.map = null;

tests/Tile/Image.html

@@ -25,6 +25,43 @@
         t.ok( tile.size.equals(size), "tile.size is set correctly");
     }
 
+    function test_destroy_observers(t) {
+        t.plan(2);
+
+        var map = new OpenLayers.Map('map');
+        var layer = new OpenLayers.Layer.WMS( "OpenLayers WMS", 
+            "http://labs.metacarta.com/wms/vmap0?", {layers: 'basic'}); 
+        map.addLayer(layer);
+
+        var position = new OpenLayers.Pixel(20,30);
+        var bounds = new OpenLayers.Bounds(1,2,3,4);
+        var size = new OpenLayers.Size(5,6);
+
+        // with alpha hack
+        var withAlpha = new OpenLayers.Tile.Image(layer, position, bounds, null, size);
+        withAlpha.layerAlphaHack = true;
+
+        withAlpha.draw();
+        var cacheID = withAlpha.imgDiv._eventCacheID;
+        withAlpha.destroy();
+        
+        t.eq(OpenLayers.Event.observers[cacheID], undefined, 
+             "With alpha hack: imgDiv observers are cleared in destroy");
+
+        // without alpha hack
+        var withoutAlpha = new OpenLayers.Tile.Image(layer, position, bounds, null, size);
+        withoutAlpha.layerAlphaHack = false;
+
+        withoutAlpha.draw();
+        var cacheID = withoutAlpha.imgDiv._eventCacheID;
+        withoutAlpha.destroy();
+
+        t.eq(OpenLayers.Event.observers[cacheID], undefined, 
+             "Without alpha hack: imgDiv observers are cleared in destroy");
+
+        map.destroy();
+    }
+
     function test_Tile_Image_clone (t) {
         t.plan( 9 );