Triggering loadstart and loadend events for the Image layer. Thanks for the excellent patch sky. r=me (closes #1700)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@8923 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Image.js

@@ -84,6 +84,7 @@ OpenLayers.Layer.Image = OpenLayers.Class(OpenLayers.Layer, {
      */
     destroy: function() {
         if (this.tile) {
+            this.removeTileMonitoringHooks(this.tile);
             this.tile.destroy();
             this.tile = null;
         }
@@ -166,6 +167,7 @@ OpenLayers.Layer.Image = OpenLayers.Class(OpenLayers.Layer, {
                 //create the new tile
                 this.tile = new OpenLayers.Tile.Image(this, ulPx, this.extent, 
                                                       null, this.tileSize);
+                this.addTileMonitoringHooks(this.tile);
             } else {
                 //just resize the tile and set it's new position
                 this.tile.size = this.tileSize.clone();
@@ -184,6 +186,45 @@ OpenLayers.Layer.Image = OpenLayers.Class(OpenLayers.Layer, {
         this.tileSize = new OpenLayers.Size(tileWidth, tileHeight);
     },
 
+    /** 
+     * Method: addTileMonitoringHooks
+     * This function takes a tile as input and adds the appropriate hooks to 
+     *     the tile so that the layer can keep track of the loading tiles.
+     * 
+     * Parameters: 
+     * tile - {<OpenLayers.Tile>}
+     */
+    addTileMonitoringHooks: function(tile) {
+        tile.onLoadStart = function() {
+            this.events.triggerEvent("loadstart");
+        };
+        tile.events.register("loadstart", this, tile.onLoadStart);
+      
+        tile.onLoadEnd = function() {
+            this.events.triggerEvent("loadend");
+        };
+        tile.events.register("loadend", this, tile.onLoadEnd);
+        tile.events.register("unload", this, tile.onLoadEnd);
+    },
+
+    /** 
+     * Method: removeTileMonitoringHooks
+     * This function takes a tile as input and removes the tile hooks 
+     *     that were added in <addTileMonitoringHooks>.
+     * 
+     * Parameters: 
+     * tile - {<OpenLayers.Tile>}
+     */
+    removeTileMonitoringHooks: function(tile) {
+        tile.unload();
+        tile.events.un({
+            "loadstart": tile.onLoadStart,
+            "loadend": tile.onLoadEnd,
+            "unload": tile.onLoadEnd,
+            scope: this
+        });
+    },
+    
     /**
      * APIMethod: setUrl
      *