PreferenceFragment里发送广播问题

public Dialog onCreateDialog(int id) {
        switch (id) {
        case DLG_CONFIRM_UNMOUNT:
                return new AlertDialog.Builder(getActivity())
                    .setTitle(R.string.dlg_confirm_unmount_title)
                    .setPositiveButton(R.string.dlg_ok, new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int which) {
                            //我在这里发送了广播
                            Intent intent = new Intent();
                            intent.setAction(ACTION_DIS_WARNNING);
                            getActivity().sendBroadcast(intent);
                            doUnmount();
                        }})
                    .setNegativeButton(R.string.cancel, null)
                    .setMessage(R.string.dlg_confirm_unmount_text)
                    .create();
        case DLG_ERROR_UNMOUNT:
                return new AlertDialog.Builder(getActivity())
            .setTitle(R.string.dlg_error_unmount_title)
            .setNeutralButton(R.string.dlg_ok, null)
            .setMessage(R.string.dlg_error_unmount_text)
            .create();
        }
        return null;
    }

这里我用一个广播来控制一个原有的dialog的显示，但是我在那边根本接受不到这个广播，这个文件是个PreferenceFragment，我想知道是不是Cotext的问题，求大神帮帮忙