private void showProgressDialog() {
        if (mDialog == null) {
            mDialog = new ProgressDialog(getActivity());
            mDialog.setIndeterminate(true);
            mDialog.setMessage(getString(R.string.boxing_handling));
        }
        if (!mDialog.isShowing()) {
            mDialog.show();
        }
    }
the most easy to implement {@link PickerContract.View} to show medias with google's Bottom Sheet </br>
for simplest purpose, it only support SINGLE_IMG and VIDEO Mode.
for MULTI_IMG mode, use {@link BoxingViewFragment} instead.

@author ChenSL
boxing-impl/src/main/java/com/bilibili/boxing_impl/ui/BoxingBottomSheetFragment.java