如何在Android中启动活动之前显示进度对话框？

public class ProgressDialogFragment extends DialogFragment {
    public static ProgressDialogFragment newInstance() {
        ProgressDialogFragment fragment = new ProgressDialogFragment();
        return fragment;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        ProgressDialog dialog = new ProgressDialog(getActivity());
        dialog.setMessage("正在加载，请稍候...");
        dialog.setIndeterminate(true);
        dialog.setCancelable(false);
        return dialog;
    }
}

private void showProgressDialog() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    ProgressDialogFragment progressDialogFragment = ProgressDialogFragment.newInstance();
    progressDialogFragment.show(fragmentTransaction, "progress_dialog");
}

private void dismissProgressDialog() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    ProgressDialogFragment progressDialogFragment = (ProgressDialogFragment) fragmentManager.findFragmentByTag("progress_dialog");
    if (progressDialogFragment != null) {
        progressDialogFragment.dismiss();
    }
}