values_strings_strings.xml：
<!--    私密模式  -->
<string name="Secret">Secret</string>
<string name="Quit_Secret">Quit_Secret</string>

menu_sub_folder.xml：
<!--    私密模式  -->
    <item
        android:id="@+id/menu_secret"
        android:title="@string/Secret"/>
    <item
        android:id="@+id/menu_quit_secret"
        android:title="@string/Quit_Secret"/>
//    私密模式

NotesListActivity类：
    public static int secret_mode = 0;
private void startAsyncNotesListQuery() {
        String selection = (mCurrentFolderId == Notes.ID_ROOT_FOLDER) ? ROOT_FOLDER_SELECTION
                : NORMAL_SELECTION;
        if(secret_mode == 0) {
            mBackgroundQueryHandler.startQuery(FOLDER_NOTE_LIST_QUERY_TOKEN, null,
                    Notes.CONTENT_NOTE_URI, NoteItemData.PROJECTION, selection, new String[]{
                            String.valueOf(mCurrentFolderId)
                    }, NoteColumns.TYPE + " DESC," + NoteColumns.MODIFIED_DATE + " DESC");
        }
        else{
            String str1 = "111";
            String [] PROJECTION = new String [] {  //定义一个新的PROJECTION数组，只换掉SNIPPET
                    NoteColumns.ID,
                    NoteColumns.ALERTED_DATE,
                    NoteColumns.BG_COLOR_ID,
                    NoteColumns.CREATED_DATE,
                    NoteColumns.HAS_ATTACHMENT,
                    NoteColumns.MODIFIED_DATE,
                    NoteColumns.NOTES_COUNT,
                    NoteColumns.PARENT_ID,
//                    NoteColumns.SNIPPET,
                    str1,
                    NoteColumns.TYPE,
                    NoteColumns.WIDGET_ID,
                    NoteColumns.WIDGET_TYPE,
            };
            mBackgroundQueryHandler.startQuery(FOLDER_NOTE_LIST_QUERY_TOKEN, null,
                    Notes.CONTENT_NOTE_URI, PROJECTION, selection, new String[]{
                            String.valueOf(mCurrentFolderId)
                    }, NoteColumns.TYPE + " DESC," + NoteColumns.MODIFIED_DATE + " DESC");

        }
    }