添加注释

src/Notes-master1/app/src/main/java/net/micode/notes/data/NotesDatabaseHelper.java

@@ -28,10 +28,13 @@ import net.micode.notes.data.Notes.NoteColumns;
 
 
 public class NotesDatabaseHelper extends SQLiteOpenHelper {
+    // 数据库名称
     private static final String DB_NAME = "note.db";
 
+    // 数据库版本号
     private static final int DB_VERSION = 4;
 
+    // 表名
     public interface TABLE {
         public static final String NOTE = "note";
 
@@ -42,6 +45,7 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
 
     private static NotesDatabaseHelper mInstance;
 
+    // 创建note表的sql语句
     private static final String CREATE_NOTE_TABLE_SQL =
         "CREATE TABLE " + TABLE.NOTE + "(" +
             NoteColumns.ID + " INTEGER PRIMARY KEY," +
@@ -106,7 +110,6 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
         "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
         "  AND " + NoteColumns.NOTES_COUNT + ">0" + ";" +
         " END";
-
     /**
      * Increase folder's note count when insert new note to the folder
      */
@@ -206,6 +209,7 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
         "  WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
         " END";
 
+   // 创建NotesDatabaseHelper类，用于创建数据库，并创建note表，触发器，系统文件夹
     public NotesDatabaseHelper(Context context) {
         super(context, DB_NAME, null, DB_VERSION);
     }
@@ -216,8 +220,8 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
         createSystemFolder(db);
         Log.d(TAG, "note table has been created");
     }
-
    private void reCreateNoteTableTriggers(SQLiteDatabase db) {
+        // 删除已存在的触发器，如果它们存在
         db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_update");
         db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_update");
         db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_delete");
@@ -226,6 +230,7 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
         db.execSQL("DROP TRIGGER IF EXISTS folder_delete_notes_on_delete");
         db.execSQL("DROP TRIGGER IF EXISTS folder_move_notes_on_trash");
 
+        // 创建新的触发器，使用新的触发器创建触发器函数
         db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);
         db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);
         db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER);
@@ -288,6 +293,7 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
     }
 
     static synchronized NotesDatabaseHelper getInstance(Context context) {
+        // 获取NotesDatabaseHelper实例，如果mInstance为空，则创建一个新的实例
         if (mInstance == null) {
             mInstance = new NotesDatabaseHelper(context);
         }
@@ -296,33 +302,40 @@ public class NotesDatabaseHelper extends SQLiteOpenHelper {
 
     @Override
     public void onCreate(SQLiteDatabase db) {
+        // 创建note表和data表
         createNoteTable(db);
         createDataTable(db);
     }
 
     @Override
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+        // 判断是否需要重新创建触发器
         boolean reCreateTriggers = false;
+        // 是否跳过v2升级
         boolean skipV2 = false;
 
         if (oldVersion == 1) {
+            // 升级到v2
             upgradeToV2(db);
             skipV2 = true; // this upgrade including the upgrade from v2 to v3
             oldVersion++;
         }
 
         if (oldVersion == 2 && !skipV2) {
+            // 升级到v3
             upgradeToV3(db);
             reCreateTriggers = true;
             oldVersion++;
         }
 
         if (oldVersion == 3) {
+            // 升级到v4
             upgradeToV4(db);
             oldVersion++;
         }
 
         if (reCreateTriggers) {
+            // 重新创建触发器
             reCreateNoteTableTriggers(db);
             reCreateDataTableTriggers(db);
         }