source: Dev/trunk/src/client/dojox/grid/_SelectionPreserver.js

define([
        "dojo/_base/declare",
        "dojo/_base/connect",
        "dojo/_base/lang",
        "dojo/_base/array"
], function(declare, connect, lang, array){

return declare("dojox.grid._SelectionPreserver", null, {
        // summary:
        //              Preserve selections across various user actions.
        //
        // description:
        //              When this feature is turned on, Grid will try to preserve selections across actions, e.g. sorting, filtering etc.
        //
        //              Precondition - Identifier(id) is required for store since id is the only way for differentiating row items.
        //              Known issue - The preserved selections might be inaccurate if some unloaded rows are previously selected by range(e.g.SHIFT + click)
        //
        // example:
        // |    //To turn on this - please set 'keepSelection' attribute to true
        // |    <div dojoType="dojox.grid.DataGrid" keepSelection = true .../>
        // |    <div dojoType="dojox.grid.TreeGrid" keepSelection = true .../>
        // |    <div dojoType="dojox.grid.LazyTreeGrid" keepSelection = true .../>
        
        constructor: function(selection){
                this.selection = selection;
                var grid = this.grid = selection.grid;
                this.reset();
                this._connects = [
                        connect.connect(grid, '_setStore', this, 'reset'),
                        connect.connect(grid, '_addItem', this, '_reSelectById'),
                        connect.connect(selection, 'onSelected', lang.hitch(this, '_selectById', true)),
                        connect.connect(selection, 'onDeselected', lang.hitch(this, '_selectById', false)),
                        connect.connect(selection, 'deselectAll', this, 'reset')
                ];
        },
        destroy: function(){
                this.reset();
                array.forEach(this._connects, connect.disconnect);
                delete this._connects;
        },
        reset: function(){
                this._selectedById = {};
        },
        _reSelectById: function(item, index){
                // summary:
                //              When some rows is fetched, determine whether it should be selected.
                if(item && this.grid._hasIdentity){
                        this.selection.selected[index] = this._selectedById[this.grid.store.getIdentity(item)];
                }
        },
        _selectById: function(toSelect, inItemOrIndex){
                // summary:
                //              Record selected rows by ID.
                if(this.selection.mode == 'none' || !this.grid._hasIdentity){ return; }
                var item = inItemOrIndex, g = this.grid;
                if(typeof inItemOrIndex == "number" || typeof inItemOrIndex == "string"){
                        var entry = g._by_idx[inItemOrIndex];
                        item = entry && entry.item;
                }
                if(item){
                        this._selectedById[g.store.getIdentity(item)] = !!toSelect;
                }
                return item;
        }
});
});