grid.getSelectionModel().getSelections()其中grid.getSelectionModel()实际上是选择了该gird的sm，例：var sm = new xg.CheckboxSelectionModel();
var grid2 = new xg.GridPanel({
store: new Ext.data.Store({
reader: reader,
data: xg.dummyData
}),
cm: new xg.ColumnModel([
sm,
...
