Commit a change to the Strategy/Fixed to behave more like GeoRSS/Text/GML

layers, and not load by default if the layer is not visible. Includes tests.
Default Behavior can be changed with 
'OpenLayers.Strategy.Fixed.prototype.preload=true;'. With review from elemoine,
comments from tschaub, review from me. Patch by Edgemaster. (Closes #1852) 


git-svn-id: http://svn.openlayers.org/trunk/openlayers@8775 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Strategy/Fixed.js

@@ -14,6 +14,14 @@
  *  - <OpenLayers.Strategy>
  */
 OpenLayers.Strategy.Fixed = OpenLayers.Class(OpenLayers.Strategy, {
+    
+    /**
+     * APIProperty: preload
+     * {Boolean} Load data before layer made visible. Enabling this may result
+     *   in considerable overhead if your application loads many data layers
+     *   that are not visible by default. Default is true.
+     */
+    preload: false,
 
     /**
      * Constructor: OpenLayers.Strategy.Fixed
@@ -37,8 +45,7 @@ OpenLayers.Strategy.Fixed = OpenLayers.Class(OpenLayers.Strategy, {
 
     /**
      * Method: activate
-     * Activate the strategy: reads all features from the protocol and add them 
-     * to the layer.
+     * Activate the strategy: load data or add listener to load when visible
      *
      * Returns:
      * {Boolean} True if the strategy was successfully activated or false if
@@ -46,14 +53,33 @@ OpenLayers.Strategy.Fixed = OpenLayers.Class(OpenLayers.Strategy, {
      */
     activate: function() {
         if(OpenLayers.Strategy.prototype.activate.apply(this, arguments)) {
-            this.layer.protocol.read({
-                callback: this.merge,
-                scope: this
-            });
+            if(this.layer.visibility == true || this.preload) {
+                this.load();
+            } else {
+                this.layer.events.on({
+                    "visibilitychanged": this.load,
+                    scope: this
+                });
+            }
             return true;
         }
         return false;
     },
+    
+    /**
+     * Method: load
+     * Tells protocol to load data and unhooks the visibilitychanged event
+     */
+    load: function() {
+        this.layer.protocol.read({
+            callback: this.merge,
+            scope: this
+        });
+        this.layer.events.un({
+            "visibilitychanged": this.load,
+            scope: this
+        });
+    },
 
     /**
      * Method: merge