Q:

How do you set fieldset title dynamically in Sench Touch 2? 

I would like to set fieldset titles dynamically.  I have a form with 1 or many fieldsets.  I would like the fieldset title to be numbered sequentially 1 of 3, 2 of 3, and 3 of 3.  For example here is some code in the form controller:
var formView = this.getFormView(),
fieldsets = formView.down('fieldset');

for (var i = 0, len = fieldsets.length; i < len; i++) {
    fieldsets[i].setTitle((i + 1) + ' of ' + len)
}

I was thinking of getting the items of the form panel formView.getItems() and finding the fieldsets that way, but I am sure there is an easier way to get the fieldsets and then setting their titles dynamically. 

A:

I have worked on your problem.  As you have not given the coding of your 'View.js' ,so i have created my own View - 'demo.js'. 
 Ext.define("Stackoverflow.view. Demo", {
 extend: "Ext.form. Panel",
 config: {
    scrollable: 'vertical',
    items: [
        {
            xtype: "toolbar",
            docked: "top",
            title: "Set Title Dynamically ",
            items: [
                {
                    xtype: "button",
                    ui: "action",
                    text: "Set Title",
                    itemId: "settitle"
                }
            ]
        },

        { xtype: "fieldset",
          id: 'field1',
          title: 'oldtitle',
            items: [
                {
                    xtype: 'textfield',
                    name: 'name',
                    label: 'Name'
                }

            ]
        }

    ],
    listeners: [
        {
            delegate: "#settitle",
            event: "tap",
            fn: "onSetTitle"
        },
    ]
},

onSetTitle: function () {
   console.log("title");
   var z=Ext.getCmp('field1');
   z.setTitle('newtitle');
}

});

Might be this will help you.  
For any queries feel free to ask. 
Bye.