openlayers2地图控件扩展：要素删除DeleteFeature

实现要素删除控件，扩展OpenLayers.Control类，实现效果：选择DeleteFeature工具后，选择要素，按delete键删除要素（这里的删除只是将feature设置成delete状态，需提交到远程服务器才能删除数据源中的要素），具体代码如下：

 OpenLayers.Control.DeleteFeature = OpenLayers.Class(OpenLayers.Control.SelectFeature, {
     deleteCodes: null,

     /*
      * layers--Array[]
      * options--Object{}
      * */
     initialize: function(layers, options) {
         var me = this;
         me.deleteCodes = [46, 68];
         OpenLayers.Control.SelectFeature.prototype.initialize.apply(this, arguments);
         me.keyboard = new OpenLayers.Handler.Keyboard(this,{
             keydown: me.handleKeypress,
             scope: me
         });
     },
     handleKeypress: function(evt){
         var code = evt.keyCode;
         // check for delete key
         if(OpenLayers.Util.indexOf(this.deleteCodes, code) != -1){
             var feature = this.handlers.feature.feature;
             if(!feature)
                 return;

             // if feature doesn't have a fid, destroy it
             if(feature.fid == undefined) {
                 this.layers[0].destroyFeatures([feature]);
             } else {
                 feature.state = OpenLayers.State.DELETE;
                 this.layers[0].events.triggerEvent("afterfeaturemodified",
                         {feature: feature});
                 this.layers[0].drawFeature(feature);
             }
         }
     },
     setMap: function(map) {
         this.keyboard.setMap(map);
         OpenLayers.Control.SelectFeature.prototype.setMap.apply(this, arguments);
     },
     activate: function() {
         return (this.keyboard.activate() &&
                 OpenLayers.Control.SelectFeature.prototype.activate.apply(this, arguments));
     },
     deactivate: function() {
         this.keyboard.deactivate();
         OpenLayers.Control.SelectFeature.prototype.deactivate.apply(this, arguments);
     },
     CLASS_NAME: "OpenLayers.Control.DeleteFeature"
 });

效果