Two constants named DATE_KEY

When the intent is set in ForecastFragment, you use DetailActivity.DATE_KEY as the key of the extra content.
When you pull back the data from the intent in the Detail Fragment, you use intent.hasExtra(DATE_KEY) but, as you also have declared a constant inside your fragment, it searches with the wrong key.
In my phone, the Detail View shows empty until I made the changes proposed or, maybe easier, just leave the code as you wrote it but deleting the DATE_KEY constant declared inside the fragment.