System.InvalidCastException "Object must implement IConvertible." when deserializing a Dictionary using a BinaryFormatter

Question

[Serializable]
public class CustomFields : MyObject, ICustomFields // MyObject is marked as ISerializable
{
    private IDictionary<string, string> _customFieldDictionary;

    public CustomFields( ) {
        this._customFieldDictionary = new Dictionary<string, string>( );
    }

    protected CustomFields( SerializationInfo info, StreamingContext context )
        : base( info, context )
    {
        if( info == null )
            throw new System.ArgumentNullException( "info" );

        // Following line throws
        this.CustomFieldDictionary = ( Dictionary<string, string> ) info.GetValue( "CustomFieldDictionary", typeof( Dictionary<string, string> ) );
    }

    [SecurityPermission( SecurityAction.LinkDemand,
        Flags = SecurityPermissionFlag.SerializationFormatter )]
    public override void GetObjectData( SerializationInfo info, StreamingContext context )
    {
        if( info == null )
            throw new ArgumentNullException( "info" );

        base.GetObjectData( info, context );

        info.AddValue( "CustomFieldDictionary", this.CustomFieldDictionary, typeof( Dictionary<string, string> ) );
    }

    public virtual IDictionary<string, string> CustomFieldDictionary
    {
        get { return this._customFieldDictionary; }
        set { this._customFieldDictionary = value; }
    }
}

This class is referenced by another Serializable class.

[Serializable]
public class UserOfCustomFields : MyObject, IUserOfCustomFields {

    public UserOfCustomFields( ) {
        this.CustomFields = new CustomFields( );
    }

    protected UserOfCustomFields( SerializationInfo info, StreamingContext context ) : base(info, context)
    {
        if( info == null )
            throw new System.ArgumentNullException( "info" );
        this.CustomFields = ( CustomFields ) info.GetValue( "CustomFields", typeof( CustomFields ) );
    }

    [SecurityPermission(SecurityAction.LinkDemand,
        Flags = SecurityPermissionFlag.SerializationFormatter)]
    public override void GetObjectData( SerializationInfo info, StreamingContext context )
    {
        if( info == null )
            throw new ArgumentNullException( "info" );

        base.GetObjectData( info, context );

        info.AddValue( "CustomFields", this.CustomFields, typeof( CustomFields ) );
    }

    public virtual ICustomFields CustomFields { get; set; }
}

Here's the code that calls the serialization/deserialization code:

    public bool SaveObjects( IEnumerable<IMyObject> objects ) {
        // If we have null objects fail
        if ( objects == null ) { return false; }

        var local_objects = objects.ToList( );
        var new_list = new List< IDBObject< Guid > >( );
        foreach ( var obj in local_objects ) {
            var clone = this.DeepCopy( obj );
            new_list.Add( clone );
        }

        return true;
    }

And the actual serialization/deserialization takes place here:

    public virtual T DeepCopy<T>( T obj )
    {
        if( !obj.GetType( ).IsSerializable )
        {
            throw new Exception( "The source object must be serializable" );
        }

        if( Object.ReferenceEquals( obj, null ) )
        {
            throw new Exception( "The source object must not be null" );
        }

        T result = default( T );

        using( var memoryStream = new MemoryStream( ) )
        {
            var formatter = new BinaryFormatter( );
            formatter.Serialize( memoryStream, obj );
            memoryStream.Seek( 0, SeekOrigin.Begin );

            result = ( T ) formatter.Deserialize( memoryStream );

            memoryStream.Close( );
        }

        return result;
    }

As noted in the title I get System.InvalidCastException "Object must implement IConvertible." when deserializing. Is Dictionary a special case? I've had no problems with any other types (up to now).

Set debugger to break on unhandled exception. You will probably find that it is object inside the dictionary which doesn't implement IConvertible — Ben, Aug 22 '18 at 21:24
It shouldn't have to. I did discover that the underlying type was actually NHibernate.Collection.Generic.PersistentGenericMap so I guess now I need to discover why that is the case. As you can see from above it's defined as Dictionary. — D A M, Aug 23 '18 at 13:50

score 0 · Answer 1 · answered Aug 23 '18 at 14:08

Turns out that since I'm using NHibernate that it injects it's own implementation of collections. In order to make this work I must use the interface IDictionary in the serialization/deserialization:

    protected CustomFields( SerializationInfo info, StreamingContext context )
        : base( info, context )
    {
        if( info == null )
            throw new ArgumentNullException( "info" );

        this.CustomFieldDictionary = ( IDictionary<string, string> ) info.GetValue( "CustomFieldDictionary", typeof( IDictionary<string, string> ) );
    }

    [SecurityPermission( SecurityAction.LinkDemand,
        Flags = SecurityPermissionFlag.SerializationFormatter )]
    public override void GetObjectData( SerializationInfo info, StreamingContext context )
    {
        if( info == null )
            throw new ArgumentNullException( "info" );

        base.GetObjectData( info, context );

        // Following line throws
        info.AddValue( "CustomFieldDictionary", this.CustomFieldDictionary, typeof( IDictionary<string, string> ) );
    }

System.InvalidCastException "Object must implement IConvertible." when deserializing a Dictionary using a BinaryFormatter

1 Answers1