ExtJS，grid多选框列

xtype: "grid",
store: myStore,
selModel: Ext.create("Ext.selection.CheckboxModel", {
    injectCheckbox: 1,//checkbox位于哪一列，默认值为0
    mode: "single",//multi,simple,single；默认为多选multi
    checkOnly: true,//如果值为true，则只用点击checkbox列才能选中此条记录
    allowDeselect: true,//如果值true，并且mode值为单选（single）时，可以通过点击checkbox取消对其的选择
    enableKeyNav: true
}),
columns: [
    { xtype: "rownumberer", text: "行号", width: 50 },
    { text: "姓名", dataIndex: "Name" },
    { text: "年龄", dataIndex: "Age" }
]

var grid = win.down("grid");
var records = grid.getSelectionModel().getSelection();
Ext.MessageBox.alert("提示", records.length);

        var me = this,
        records = me.selection();
        Ext.MessageBox.alert("提示", records.length);