DialogFragment.getDialog returns null

You're calling getDialog() too early in the DialogFragment's life cycle.

getDialog() simply returns the private variable mDialog from the DialogFragment.

When a DialogFragment is instantiated mDialog is null, and then it gets set when onCreateDialog is fired inside getLayoutInflater(Bundle savedInstanceState), so you have to call getDialog after onCreateDialog.

For example, the order of some common methods called is onCreate, onCreateDialog, and onCreateView, onStart. So, you can call getDialog and have it return something in onCreateView or onStart, but not in onCreate or onCreateDialog.

Even though onStart is called called when the Fragment is visible to the user, adjusting the layout of the fragment at that point looks fine.... for example setting the width and height using getDialog().getWindow().setLayout(..., ...); doesn't make the fragment appear to change size, but just appears to have the newly set size.

Try calling executePendingTransactions() from the available FragmentManager.

    dialogFragment = new DialogFragment();
        ...
    dialogFragment.show(mFragmentActivity.getSupportFragmentManager(), "Dialog");
    mFragmentActivity.getSupportFragmentManager().executePendingTransactions();

    Dialog d = dialogFragment.getDialog()
        ...