What I have done to make this work is the following. Some of it will vary depending upon where the code is located. Basically I create an empty container called WorkArea at the top level, then I drag it into the Main View to create a link. In my case my Main View is a VBox with a header, work area, footer combo.
To move my various "worker" views into the WorkArea I do the following within a View Controller
Of course I do add checks to make sure all the objects are valid before making the calls. Also if you've named your app something besides the default (MyApp), use that in the class path.
var cont = this.GetWorkArea();
var viewToLoad = Ext.create(MyApp.view.ViewToLoad); // name of actual view class
Now, initial view was an issue for me, since work area is blank by default. The way I got this to work was adding similar code to the "afterLayout" event of the Main View. Looks like this...
Not sure if it makes a memory difference, but I do have AutoDestroy set to true on my views. Good luck...
var cont = this.down('#workArea');
var viewToLoad = Ext.create(MyApp.view.LoginPanel);