无法防止 SQLiteConnection 对象泄漏

Question

在我的 Android 应用程序中，我有一些使用 SQLite 的数据库事务，但尽管尝试了很多方法来防止泄漏，但我还是遇到了 SQLiteConnection 对象泄漏。我几乎尝试了互联网上的每一件事，比如关闭数据库、关闭游标或结束事务。以下是 android studio 中的警告。

A SQLiteConnection object for database '/data/user/0/com.example.myapp/databases/myapp.dbnotes.db' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.

有时通过关闭数据库或关闭游标我曾经得到错误 - Attempt to reopen an already-closed object ....。我不是 Android 的专家，我正在尝试自己学习，所以你能帮助我吗？我已经发布了以下代码：

DBHelper 内部 class

  public class DBHelper extends SQLiteOpenHelper {

    ...
      public static DBHelper getInstance(Context ctx) {

      if (mInstance == null) {
        mInstance = new DBHelper(ctx.getApplicationContext());
       }
       return mInstance;
     }

     private DBHelper(Context context) {
       super(context, DB_NAME, null, 1);
       this.context = context;
       DB_PATH = context.getDatabasePath(DB_NAME).getPath();
    }

   ...

   private Cursor getData(String Query) {
      String myPath = DB_PATH + DB_NAME;
      Cursor c = null;
     try {
          db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
          c = db.rawQuery(Query, null);
        } catch (Exception e) {
          e.printStackTrace();
         }
      return c;
     }

   private void dml(String Query) {
      String myPath = DB_PATH + DB_NAME;
      if (db == null)
        db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
      try {
         db.execSQL(Query);
      } catch (Exception e) {
         e.printStackTrace();
      }
    }




  //Methods to perform different db transaction

  public void addToSubject(ItemSubject itemSubject) {
   if (checkSuggested(itemSubject.getId())) {
     dml("delete from " + TABLE_SUBJECT + " where id = '" + itemSubject.getId() + "'");
   }
   String insert = "insert into TABLE_SUBJECT .....";
   dml(insert);
 }

 public void cleartable_subject() {
   String delete = "delete from " + TABLE_SUBJECT;
   dml(delete);
 }

public long subject_size() {
   if (db == null) {
     db = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READWRITE);
   }
   try {
     long count = DatabaseUtils.queryNumEntries(db, TABLE_SUBJECT);
     return count;
   } catch (Exception e) {
     e.printStackTrace();
     return 0;
  }
 }

 private Boolean checkSubject(String id) {
   String select = "select * from " + TABLE_SUBJECT + " where id = '" + id + "'";
   Cursor cursor = getData(select);
   return cursor != null && cursor.getCount() > 0;
 }

 public ArrayList<ItemSubject> loadDataSubject() {
    ArrayList<ItemSubject> arrayList = new ArrayList<>();
    String select = "select * from " + TABLE_SUBJECT;
    Cursor cursor = getData(select);
    if (cursor != null && cursor.getCount() > 0) {
     cursor.moveToFirst();
     for (int i = 0; i < cursor.getCount(); i++) {
         String id = cursor.getString(cursor.getColumnIndex(TAG_ID));
         String course = cursor.getString(cursor.getColumnIndex(TAG_COURSE_NAME));
         ....
         ItemSubject objItem = new ItemSubject(id, courseId,...);
         arrayList.add(objItem);
         cursor.moveToNext();
     }
     cursor.close();
    }
    return arrayList;
   }

   //There are more similar methods for other tables

我正在像

这样的片段和活动中访问这些方法

     dbHelper = DBHelper.getInstance(getActivity());

     if ((dbHelper.subject_size() >= 1){
      dbHelper.cleartable_subject();
      for (int i = 0; i < arrayListSubject.size(); i++) {
                dbHelper.addToSubject(arrayListSubject.get(i));
            }
            arrayListSubject = dbHelper.loadDataSubject();
     }

抱歉，代码太长了，但我认为一切都是必要的。你能帮帮我吗？

Answer 1

你说你在网上查了很多问题，但你肯定没查this or this。它确实在搜索 5 分钟后突然出现。

无论如何，如果我是你，要解决这个问题，我会在关闭连接时包含一个 finally 子句。这意味着您会将数据库助手声明为静态实例变量，并使用抽象工厂模式来保证单例属性.

您发出警告是因为您无法确保在任何给定时间只会存在一个 DatabaseHelper。如果 mInstance 对象还没有被初始化，一个将被创建。如果已经创建了一个，那么它将被简单地返回。

代码如下：

public ArrayList<ItemSubject> loadDataSubject() {
    ArrayList<ItemSubject> arrayList = new ArrayList<>();
    String select = "select * from " + TABLE_SUBJECT;
    Cursor cursor = getData(select);
    
    
    if (cursor != null && cursor.getCount() > 0) {
    try {
        cursor.moveToFirst();
            for (int i = 0; i < cursor.getCount(); i++) {
                String id = cursor.getString(cursor.getColumnIndex(TAG_ID));
                String course = cursor.getString(cursor.getColumnIndex(TAG_COURSE_NAME));
         ....
                ItemSubject objItem = new ItemSubject(id, courseId,...);
                arrayList.add(objItem);
                cursor.moveToNext();
           }
       finally {
           if (cursor != null)
           cursor.close();
       }
   }
   return arrayList;
}

但是既然你说我对你的问题（已经在其他帖子中回答过）的唯一贡献是改进你缺乏的基础英语，那么我不确定你是否可以接受这个作为一个足够的回答。

无法防止 SQLiteConnection 对象泄漏

Unable to prevent SQLiteConnection object leakage

java

android

memory-leaks

android-sqlite