问如何在extjs中单击事件按钮将值设置为组合框

EN

var count = 0;

var btn = Ext.create('Ext.Button', {
    text: 'Click me',
    handler: function() {
        count++;

        var combo = Ext.create('Ext.form.ComboBox', {
            fieldLabel: 'Choose State',
            store: states,
            displayField: 'name',
            value: count,
            valueField: 'id'
        });

        container.add(combo);
    }
});