c# - SQLiteOpenHelper - 无法访问已处置的对象

问题描述

我有一个我的SQLiteOpenHelper类，它是作为单例编写的。我应该注意，我不是在 Java 中执行此操作，而是使用 Xamarin.Android C# 来编写它。

这是该课程的一个片段：

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那是一个单例，在活动和服务中像这样使用：

服务：

[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);
    }

}

活动，实际上是BaseActivity所有活动都继承自：

[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);
    }

}

该DatabaseHelper实例被频繁地处理，导致服务或活动尝试访问被处理的_database对象。

这是如何处理的，为什么？

我认为在_instance内部制作静态DatabaseHelper以及使构造函数私有并强制使用该方法会保留一个不会在活动和服务之间处理DatabaseHelper.Instance的单个实例？DatabaseHelper

我误解了这个吗？

编辑来自 try/catch 块的 logcat 输出，显示抛出的异常。该SaveHeartbeat方法存在于基础活动中。：

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);
            }
        }

编辑 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，所以我的理论是，当我访问语句db中的对象时，using()它正在处理DatabaseHelper对象使用的数据库。还注意到我没有使用db.InsertOrThrow()我应该使用的方法。要对我的班级进行一些重新工作DatabaseHelper，看看是否能解决问题。

标签： c#androidxamarin.androidsqliteopenhelper

解决方案

事实证明，我的单例实例DatbaseHelper没有被处理掉。

实际上发生的事情是我正在处理辅助方法中SQLiteDatabase的 from 正在使用的对象。DatbaseHelper

要真正解决这个问题，我所要做的就是改变：

/// <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;

}

概括：

通过在我的辅助方法内的语句中初始化我的SQLiteDatabase db对象，我正在处理我需要的。using()SQLiteDatabaseDatabaseHelper

c# - SQLiteOpenHelper - 无法访问已处置的对象

问题描述

解决方案

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