Added WCF.PageVisibilityHandler

diff --git a/wcfsetup/install/files/js/WCF.js b/wcfsetup/install/files/js/WCF.js
index 3cc1c9672c9b182e8fd68d61d709c88537d7d444..61d2400e148ca6ef59752cc195a2b28228227585 100755 (executable)
--- a/wcfsetup/install/files/js/WCF.js
+++ b/wcfsetup/install/files/js/WCF.js
@@ -5292,6 +5292,107 @@ WCF.DOMNodeRemovedHandler = {
        }
 };
 
+WCF.PageVisibilityHandler = {
+       /**
+        * list of callbacks
+        * @var WCF.Dictionary
+        */
+       _callbacks: new WCF.Dictionary(),
+       
+       /**
+        * indicates that event listeners are bound
+        * @var boolean
+        */
+       _isListening: false,
+       
+       /**
+        * name of window's hidden property
+        * @var string
+        */
+       _hiddenFieldName: '',
+       
+       /**
+        * Adds a new callback.
+        * 
+        * @param       string          identifier
+        * @param       object          callback
+        */
+       addCallback: function(identifier, callback) {
+               this._bindListener();
+               
+               if (this._callbacks.isset(identifier)) {
+                       console.debug("[WCF.PageVisibilityHandler] identifier '" + identifier + "' is already bound to a callback");
+                       return false;
+               }
+               
+               this._callbacks.add(identifier, callback);
+       },
+       
+       /**
+        * Removes a callback from list.
+        * 
+        * @param       string          identifier
+        */
+       removeCallback: function(identifier) {
+               if (this._callbacks.isset(identifier)) {
+                       this._callbacks.remove(identifier);
+               }
+       },
+       
+       /**
+        * Binds click event handler.
+        */
+       _bindListener: function() {
+               if (this._isListening) return;
+               
+               var $eventName = null;
+               if (typeof document.hidden !== "undefined") {
+                       this._hiddenFieldName = "hidden";
+                       $eventName = "visibilitychange";
+               }
+               else if (typeof document.mozHidden !== "undefined") {
+                       this._hiddenFieldName = "mozHidden";
+                       $eventName = "mozvisibilitychange";
+               }
+               else if (typeof document.msHidden !== "undefined") {
+                       this._hiddenFieldName = "msHidden";
+                       $eventName = "msvisibilitychange";
+               }
+               else if (typeof document.webkitHidden !== "undefined") {
+                       this._hiddenFieldName = "webkitHidden";
+                       $eventName = "webkitvisibilitychange";
+               }
+               
+               if ($eventName === null) {
+                       console.debug("[WCF.PageVisibilityHandler] This browser does not support the page visibility API.");
+               }
+               else {
+                       $(document).on($eventName, $.proxy(this._executeCallbacks, this));
+               }
+               
+               this._isListening = true;
+       },
+       
+       /**
+        * Executes callbacks if page is hidden/visible again.
+        */
+       _executeCallbacks: function(event) {
+               if (this._isExecuting) return;
+               
+               // do not track events while executing callbacks
+               this._isExecuting = true;
+               
+               var $state = document[this._hiddenFieldName];
+               this._callbacks.each(function(pair) {
+                       // execute callback
+                       pair.value($state);
+               });
+               
+               // enable listener again
+               this._isExecuting = false;
+       }
+};
+
 /**
  * Namespace for table related classes.
  */