I found an answer to this problem. I changed the code so that I don't have to call the initialize function. Instead, I put everything in the config settings.
Ext.define("AccessibleMap.view.ChooseView", {
extend: "Ext.form.Panel",
alias: "widget.chooseview",
config:{
layout:{
type: 'vbox',
pack: 'center'
},
items:[{
xtype: "toolbar",
docked: "top",
title: "Accessible Map",
},{
xtype: 'container',
flex: 1,
layout:{
type: 'vbox',
align: 'center'
},
items: [{
xtype: 'button',
...
}],
}],
listeners:[{ ...}]
}
});
As you can see, I defined the layout in the outer Panel to vbox with pack = center and the inner container to align = center. Moreover I defined a flex for the container.