Ext.grid.GridPanel不需按住Ctrl键单元行多选效果实现

项目中遇到需要实现在Ext.grid.GridPanel中选中单元格时，不需要按ctrl键便可多选，后来在sencha论坛上找到下面方法：重写Ext.grid.CheckboxSelectionModel中的handleMouseDown方法，该方法继承自Ext.grid.RowSelectionModel(),然后调用重写后的方法定义sm即可

Ext.override(Ext.grid.CheckboxSelectionModel, { 
    handleMouseDown : function(g, rowIndex, e){   
      if(e.button !== 0 || this.isLocked()){   
        return;   
      }   
      var view = this.grid.getView();   
      if(e.shiftKey && !this.singleSelect && this.last !== false){   
        var last = this.last;   
        this.selectRange(last, rowIndex, e.ctrlKey);   
        this.last = last; // reset the last   
        view.focusRow(rowIndex);   
      }else{   
        var isSelected = this.isSelected(rowIndex);   
        if(isSelected){   
          this.deselectRow(rowIndex);   
        }else if(!isSelected || this.getCount() > 1){   
          this.selectRow(rowIndex, true);   
          view.focusRow(rowIndex);   
        }   
      }   
    } 
});
  var sm = new Ext.grid.CheckboxSelectionModel();