SQLiteOpenHelper - 無法訪問已處置的對象

Question

我有一個我的SQLiteOpenHelper類，它被寫成一個單例。 我應該注意到我在Java中沒有這樣做，我使用Xamarin.Android C＃來編寫這個。

這是該類的一個片段：

public class DatabaseHelper : SQLiteOpenHelper
{
    private static readonly string TAG = typeof(DatabaseHelper).FullName;

    private static readonly string _databaseName = "istockdb";

    private static readonly int _databaseVersion = 32;

    private static DatabaseHelper _instance;

    private Context _context;

    private DatabaseHelper(Context context) : base(context, _databaseName, null, _databaseVersion)
    {
        _context = context;
    }

    [MethodImpl(MethodImplOptions.Synchronized)]
    public static DatabaseHelper Instance(Context context)
    {
        // *** Use the application context, which will ensure that ***
        // *** the Activity's context is not accidentally leaked ***
        return _instance ?? (_instance = new DatabaseHelper(context.ApplicationContext));
    }

}

所以我的DatabaseHelper是一個單例，在活動和服務中使用如下：

服務：

[Service(Name=Text.MobileBackgroundHbService, Enabled = true, Exported = true), IntentFilter(new []{Intents.SyncHeartbeats})]
public class BGHeartbeatService : BaseIntentService
{
    public BGHeartbeatService()
    {
        this._database = DatabaseHelper.Instance(Application.Context);
    }

    protected override void OnHandleIntent(Intent intent)
    {
        if (this._database == null)
            this._database = DatabaseHelper.Instance(Application.Context);

        if (intent.Action.Equals(Intents.SyncHeartbeats)) SyncHeartbeatRecords();

        var broadcastIntent = new Intent(Intents.MobileRefresh);
        SendBroadcast(broadcastIntent);
    }

}

Activity，實際上是所有活動繼承自的BaseActivity ：

[Activity(Label = "BaseActivity")]
public abstract class BaseActivity : AppCompatActivity
{
    /// <summary>
    /// Reference to the current context.
    /// </summary>
    protected Context _context { get; set; }

    /// <summary>
    /// "Tag" used for Log functionallity.
    /// </summary>
    protected string _tag { get; set; }

    /// <summary>
    /// Reference To <see cref="RemoteSyncServiceConnection"/>
    /// </summary>
    protected RemoteSyncServiceConnection _service_connection;

    /// <summary>
    /// Reference To The Current SessionState.
    /// </summary>
    protected SessionState _session_state;

    /// <summary>
    /// Reference To <see cref="SyncReceiver"/>
    /// </summary>
    protected SyncReceiver _sync_receiver;

    /// <summary>
    /// Base FloatingActionButton.
    /// </summary>
    protected FloatingActionButton _base_fab;

    /// <summary>
    /// Is the Fab Menu Shown / Hid.
    /// </summary>
    protected static bool _is_fab_open;

    protected IConnection _printer_connection;

    protected string _printer_address;

    protected bool _service_required;

    protected bool _receiver_required;

    protected MediaPlayer _media_player;

    protected DatabaseHelper _database;

    /// <summary>
    /// <see cref="IntentFilter"/> for the <see cref="SyncReceiver"/>
    /// </summary>
    protected readonly string[] _intent_filters =
    {
        Intents.AlarmCompleteOrders,
        Intents.AlarmHeartbeats,
        Intents.AlarmPkas,
        Intents.AlarmTrackingScans,
        Intents.MobileRefresh
    };

    #region Lifecycle Methods

    /// <summary>
    /// Application Lifecycle Method.
    /// </summary>
    /// <param name="savedInstanceState"></param>
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        // *** Initialize Xamarin.Essentials ***
        Xamarin.Essentials.Platform.Init(this, savedInstanceState);

        // *** Initialize the DatabaseHelper ***
        if(this._database == null)
            this._database = DatabaseHelper.Instance(this.ApplicationContext);
    }

}

正在處理DatabaseHelper實例經常導致服務或活動嘗試訪問已處置的_database對象。

如何處理這個以及為什么？

我想使_instance的內靜態DatabaseHelper以及使構造私有，並強制使用的DatabaseHelper.Instance方法將保持的單個實例DatabaseHelper將不布置的活動和服務之間？

我誤解了嗎？

來自try / catch塊的EDIT logcat輸出顯示拋出的異常。 SaveHeartbeat方法存在於基本活動中：

protected void SaveHeartbeat(DateTime time, string sourceActivity, [CallerMemberName] string sourceEvent = "")
        {
            try
            {
                var heartbeat = new SmartWarehouse.Shared.Models.Heartbeat(sourceActivity,
                                                                            sourceEvent,
                                                                            this._session_state.CurrentSession.ROWID.ToString());

                this._database.InsertHeartbeat(heartbeat);
            }
            catch (Exception e)
            {
                // TODO: Document Exception
                Util.Tools.Bark(e);
            }
        }

編輯2 DatabaseHelper.InsertHeartbeat（）：

/// <summary>
/// Inserts a Heartbeat record into local DB.
/// </summary>
/// <param name="heartbeat"></param>
/// <returns></returns>
public long InsertHeartbeat(Heartbeat heartbeat)
{
    if (heartbeat == null) return -2L;
    using (var db = this.WritableDatabase)
    {
        var id = -3L;
        db.BeginTransactionNonExclusive();
        try
        {
            var cv = GetContentValues(heartbeat);
            id = db.Insert(DatabaseSchema.Heartbeat.TableName, null, cv);
            db.SetTransactionSuccessful();
        }
        catch (Exception e)
        {
            // TODO: Document Exception
            Util.Tools.Bark(e);
        }
        finally
        {
            db.EndTransaction();
        }
        return id;
    }
}

好吧我的理論是，當我在using()語句中訪問db對象時，它正在處理DatabaseHelper對象使用的DatabaseHelper 。 還注意到我沒有使用我應該使用的db.InsertOrThrow()方法。我將對我的DatabaseHelper類進行一些重新處理以查看是否能解決問題。

Answer 1

事實證明，我的DatbaseHelper單例實例沒有被處理掉。

實際上發生的事情是我在幫助器方法中處理了DatbaseHelper正在使用的SQLiteDatabase對象。

實際解決問題所需要做的就是改變：

/// <summary>
/// Inserts a Heartbeat record into local DB.
/// </summary>
/// <param name="heartbeat"></param>
/// <returns></returns>
public long InsertHeartbeat(Heartbeat heartbeat)
{
    if (heartbeat == null) return -2L;
    // This using() statement is causing the disposal
    using (var db = this.WritableDatabase)
    {
        var id = -3L;
        db.BeginTransactionNonExclusive();
        try
        {
            var cv = GetContentValues(heartbeat);
            id = db.Insert(DatabaseSchema.Heartbeat.TableName, null, cv);
            db.SetTransactionSuccessful();
        }
        catch (Exception e)
        {
            // TODO: Document Exception
            Util.Tools.Bark(e);
        }
        finally
        {
            db.EndTransaction();
        }
        return id;
    }
}

至：

/// <summary>
/// Inserts a Heartbeat record into local DB.
/// </summary>
/// <param name="heartbeat"></param>
/// <returns></returns>
public long InsertHeartbeat(Heartbeat heartbeat)
{
    if (heartbeat == null) return -2L;

    // This is no longer initialized in a using() statement
    var db = this.WritableDatabase;

        var id = -3L;
        db.BeginTransactionNonExclusive();
        try
        {
            var cv = GetContentValues(heartbeat);
            id = db.Insert(DatabaseSchema.Heartbeat.TableName, null, cv);
            db.SetTransactionSuccessful();
        }
        catch (Exception e)
        {
            // TODO: Document Exception
            Util.Tools.Bark(e);
        }
        finally
        {
            db.EndTransaction();
        }
        return id;

}

摘要：

通過在我的幫助器方法中的using()語句內初始化我的SQLiteDatabase db對象，我處理了我的DatabaseHelper所需的SQLiteDatabase 。