Android GridView onResume() NullPointerException (0 children, should be 12)

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http://stackoverflow.com – I'm making an app that converts data. There are two Spinners (to specify types of data), an EditText for the user input (amount of the data), and a SeekBar in case the user is too lazy to manually type the input. Anytime the user changes the SeekBar, enters an amount and hits "enter" on the keyboard, or selects a different Spinner position, the data is converted and then displayed using a GridView. Using default values, the GridView contains 12 children. The app runs seemingly perfectly (all 12 children show up) until I try to implement onResume() to return the state. I get a NullPointerExcep (HowTos)