问如何以编程方式将工具提示添加到组合框

EN

onStartReport: function (aButton) {
    var lTip = Ext.getCmp('datasources');
    lTip.setTooltip("Information on datasource");
}

onStartReport: function (aButton) {
     var tip = Ext.create('Ext.tip.ToolTip', {
     target: 'datasources',
     html: 'Information on datasource'
     });        
}

{
    xtype: 'combo',
    itemId: 'datasources',
    name: 'datasources',
    fieldLabel: 'Data sources',
    displayField: 'description',
    valueField: 'id',
    queryMode: 'local',
    value: 0,
    forceSelection: true,
    editable: false,   
    store: {
        data: [
            {id: 0, description: 'OnLine'},
            {id: 1, description: 'History'}
        ],
        fields: [
            {name: 'id', type: 'int'},
            {name: 'description', type: 'string'}               
        ],
        autoLoad: true
    }
}