Problem with simple grid test

Hi,

I've created a simple project trying to display some data in a grid. It kind of works, the data is displayed in the grid, but the grid is strangely formatted and it is not possible for me to bring up the menu that includes : 'Sort Ascending, Sort Descending, Columns' by clicking on the grid header.

Below is my Main view file where I create the grid.

Code:

Ext.define('testApp.view.main.Main', {
    extend: 'Ext.container.Container',

    xtype: 'app-main',
    

    items: [{
        xtype: 'grid',
        store : 'Objects',

columns : [{
            text : 'Column1',
            dataIndex : 'iValue'
        }]


    }]
});

Is there something wrong in creating a grid like this? What could be the reason for lack of grid menu on column headers?