I,ve installed XDK tool and try to write a sample app.
But when i open index.html, at the top-left corner I can not see CODE|DESIGN button.
How can I show DESIGN button?
You have to create your app as an App Designer app. When you choose a blank template there is a "Use App Designer" checkbox that will convert the template into an App Designer project.
BTW -- see this FAQ > https://software.intel.com/en-us/xdk/faqs/app-designer#best-app-designer...
Thanks a lot.