ExtJs 4 get selected Rows and Cells from a Grid panel
1、How to get selected Rows from a Grid panel in ExtJs 4
   get reference to grid selection model could be rowModel or cellModel depending on what was defined in the grid definition         selType: 'cellmodel' or selType: 'rowmodel'
       seletionModel = grid.getSelectionModel()
   get array of the currently selected records
       selectedRecords = selectionModel.getSelection()
   get the value of given field definition from the first selected row
       myValue = selectedRecords[0].get('fieldName')
   loop thru selectedRecords for more records if MULTI selection was allowed
2、How to get selected Cells from a Grid panel in ExtJs 4
   To get selected cell you must used selType = cellModel. After you get reference to the selectionModel as defined above use
        getCurrentPosition( )
    Returns the current position in the format {row: row, column: column}
    After you have the current row and column get the grid view to access the cell
        cell = grid.getView().getCellByPosition({row: obj.rowIdx, column: obj.colIdx});