修改ext中拖拽和CheckboxSelectionModel冲突的问题

因为gridpanel定义了拖拽 所以致使选中gridpanel的数据行 就不能取消了
作如下扩展：

Ext.grid.RowSelectionModel.override(
{
    // FIX: added this function so it could be overrided in CheckboxSelectionModel
    handleDDRowClick: function(grid, rowIndex, e)
    {
        if(e.button === 0 && !e.shiftKey && !e.ctrlKey) {
            this.selectRow(rowIndex, false);
            grid.view.focusRow(rowIndex);
        }
    },
   
    initEvents: function ()
    {
        if(!this.grid.enableDragDrop && !this.grid.enableDrag){
            this.grid.on("rowmousedown", this.handleMouseDown, this);
        }else{ // allow click to work like normal
            // FIX: made this handler function overrideable
            this.grid.on("rowclick", this.handleDDRowClick, this);
        }

        this.rowNav = new Ext.KeyNav(this.grid.getGridEl(), {
            "up" : function(e){
                if(!e.shiftKey){
                    this.selectPrevious(e.shiftKey);
                }else if(this.last !== false && this.lastActive !== false){
                    var last = this.last;
                    this.selectRange(this.last,  this.lastActive-1);
                    this.grid.getView().focusRow(this.lastActive);
                    if(last !== false){
                        this.last = last;
                    }
                }else{
                    this.selectFirstRow();
                }
            },
            "down" : function(e){
                if(!e.shiftKey){
                    this.selectNext(e.shiftKey);
                }else if(this.last !== false && this.lastActive !== false){
                    var last = this.last;
                    this.selectRange(this.last,  this.lastActive+1);
                    this.grid.getView().focusRow(this.lastActive);
                    if(last !== false){
                        this.last = last;
                    }
                }else{
                    this.selectFirstRow();
                }
            },
            scope: this
        });

        var view = this.grid.view;
        view.on("refresh", this.onRefresh, this);
        view.on("rowupdated", this.onRowUpdated, this);
        view.on("rowremoved", this.onRemove, this);
    }
});

Ext.grid.CheckboxSelectionModel.override(
{
    // FIX: added this function to check if the click occured on the checkbox.
    //      If so, then this handler should do nothing...
    handleDDRowClick: function(grid, rowIndex, e)
    {
        var t = Ext.lib.Event.getTarget(e);
        if (t.className != "x-grid3-row-checker") {
            Ext.grid.CheckboxSelectionModel.superclass.handleDDRowClick.apply(this, arguments);
        }
    }
});

Ext.grid.GridDragZone.override(
{
    getDragData: function (e)
    {
        var t = Ext.lib.Event.getTarget(e);
        var rowIndex = this.view.findRowIndex(t);
        if(rowIndex !== false){
            var sm = this.grid.selModel;
            // FIX: Added additional check (t.className != "x-grid3-row-checker"). It may not
            //      be beautiful solution but it solves my problem at the moment.
            if ( (t.className != "x-grid3-row-checker") && (!sm.isSelected(rowIndex) || e.hasModifier()) ){
                sm.handleMouseDown(this.grid, rowIndex, e);
            }
            return {grid: this.grid, ddel: this.ddel, rowIndex: rowIndex, selections:sm.getSelections()};
        }

        return false;
    }
});