c# - Realms.NativeTable.get_string 处的 Realm 查询错误(包装器管理到 native )

Question

我正在尝试对我的第一个 Realm 数据库进行简单查询。我在尝试访问由我的查询方法返回的对象的属性时遇到错误。我有两个问题:
1.这个错误是什么意思？我很难理解它...
2. 我查询的方式正确吗？如果不是，我做错了什么？

错误日志:

[mono-rt] Stacktrace:

[mono-rt]   at <unknown> <0xffffffff>

[mono-rt]   at (wrapper managed-to-native) Realms.NativeTable.get_string >(Realms.TableHandle,intptr,intptr,intptr,intptr,bool&) <0x00057>

[mono-rt]   at Realms.RealmObject.GetStringValue (string) <IL 0x0009d, >0x00323>

[mono-rt]   at EasyVending.RCreditCard.get_holderName () <IL 0x0000e, 0x0006f>

[mono-rt]   at EasyVending.RealmManager.getCreditCard () [0x0001c] in /Users/Bernardo/Projects/EasyVending/EasyVending/DataBase/RealmManager.cs:75

[mono-rt]   at EasyVending.Android.CreditCartManagement.OnCreate (Android.OS.Bundle) [0x00111] in /Users/Bernardo/Projects/EasyVending/EasyVending.Android/Activities/CreditCartManagement.cs:89

[mono-rt]   at Android.Support.V4.App.FragmentActivity.n_OnCreate_Landroid_os_Bundle_ (intptr,intptr,intptr) <IL 0x00013, 0x000ff>

[mono-rt]   at (wrapper dynamic-method) object.13add723-97a5-4397-9c8a-e6fc23d98c3c (intptr,intptr,intptr) <IL 0x00017, 0x00043>

[mono-rt]   at (wrapper native-to-managed) object.13add723-97a5-4397-9c8a-e6fc23d98c3c (intptr,intptr,intptr) <IL 0x0001f, 0x00097>

[mono-rt] Attempting native Android stacktrace:

[mono-rt]  at ???+1 [0xbe903ac0]

[mono-rt]  at ???+1 [0x98f50ffc]

=================================================================

Got a SIGSEGV while executing native code. This usually indicates
[mono-rt] a fatal error in the mono runtime or one of the native libraries 
[mono-rt] used by your application.
[mono-rt]

[libc] Fatal signal 11 (SIGSEGV), code 1, fault addr 0x97b77168 in tid 9849 (vending_android)

=====================================

public class RCreditCard : RealmObject {
    public string holderName { get; set; }
    public string bandeira { get; set; }
    public string digitos { get; set; }
    public string token { get; set; }
}

public class RealmManager {
    private string databaseName {
        get {
            return "PayBluDatabase.db";
        }
    }
    private string androidPath {
        get {
            return Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.Personal), databaseName);
        }
    }

    public Realm getRealm() {
        return Realm.GetInstance(androidPath);
    }

    public void closeRealm(Realm realm) {
        realm.Close();
    }

    public Transaction insertCreditCard(EasyVending.CreditCard creditCard) {
        var realm = getRealm();
        using(var transaction = realm.BeginWrite()) {
            var insertedCreditCard = realm.CreateObject<RCreditCard>();

            insertedCreditCard.holderName = creditCard.HolderName;
            insertedCreditCard.bandeira = creditCard.CreditCardBrand;
            insertedCreditCard.digitos = creditCard.MaskedCreditCardNumber;
            insertedCreditCard.token = creditCard.InstantBuyKey;

            transaction.Commit();
            closeRealm(realm);
            return transaction;
        }
    }

    public Transaction removeCreditCard() {
        var realm = getRealm();
        using(var transaction = realm.BeginWrite()) {
            realm.RemoveAll<RCreditCard>();
            transaction.Commit();
            closeRealm(realm);
            return transaction;
        }
    }

    public CreditCard getCreditCard() {
        var realm = getRealm();
        var rCreditCard = realm.All<RCreditCard>().First();
        closeRealm(realm);
        var creditCard = new CreditCard() {
            CreditCardBrand = rCreditCard.bandeira,
            MaskedCreditCardNumber = rCreditCard.digitos,
            HolderName = rCreditCard.holderName
        };
        return creditCard;
    }

    public bool hasCreditCard() {
        bool answer = false;
        var realm = getRealm();
        if(realm.All<RCreditCard>().Count() > 0) {
            answer = true;
        }
        closeRealm(realm);
        return answer;
    }
}

当我尝试访问我的查询返回的 RCreditCard 对象的任何属性时发生错误:

CreditCardBrand = rCreditCard.bandeira,

来自

var rCreditCard = realm.All<RCreditCard>().First();

如果问题不够清楚，请告诉我。

Answer 1

问题是您在尝试在 getCreditCard() 中读取 rCreditCard 的属性之前关闭了 Realm 。 Realm对象中的属性是零拷贝的，它们直接访问数据库，所以一旦你关闭了realm，对象就失效了。我们应该更好地处理这种情况，目前还不清楚。感谢您向我们指出!

通常，您可能不希望经常打开和关闭 Realm ，除非这些调用发生在不同的线程上。如果您坚持这样做，您应该将 Realm.Close() 调用移到事务 using 范围之外。就像现在一样，如果在事务期间抛出某些东西，它将被回滚，但您的 Realm 不会像您预期的那样关闭。

最后，通常没有必要拥有一个反射(reflect)您的 RealmObject 类的“普通”类。当然，在您的情况下可能有一些原因，但在这里并不明显。通常，您会直接使用 RealmObject 类。