请问ColumnModel的 hiddenchange 事件怎么写啊？小低初学ext 请指教

hiddenchange : ( ColumnModel this, Number columnIndex, Boolean hidden ) 具体怎么用呢

//假如建立了一个ColumnModel
var colModel = new Ext.grid.ColumnModel([
{header: "Ticker", width: 60, sortable: true},
{header: "Company Name", width: 150, sortable: true},
{header: "Market Cap.", width: 100, sortable: true},
{header: "$ Sales", width: 100, sortable: true, renderer: money},
{header: "Employees", width: 100, sortable: true, resizable: false}
]);
//监听hiddenchange事件
colModel.on('hiddenchange',function(this,columnIndex,true){
//监听的具体内容
alert(columnIndex);
});