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Serialize a FeatureClass to XML in ESRI ArcGIS


How can I serialize an IFeatureClass object to XML?

There are some resources for using IXMLSerializer on other ArcObjects, but that won't work for IFeatureClass because it doesn't implement ISerializable.


Solution

  • I've actual found my own answer to this question. I'm posting this question and answer here for the benefit of others and for feedback/critique on my approach.

    IFeatureClass cannot be serialized directly, but IRecordSet2 can be. So the first step is implementing a method to convert IFeatureClass to IRecordSet2:

    private static IRecordSet2 ConvertToRecordset(IFeatureClass fc)
    {
        IRecordSet recSet = new RecordSetClass();
        IRecordSetInit recSetInit = recSet as IRecordSetInit;
        recSetInit.SetSourceTable(fc as ITable, null);
    
        return (IRecordSet2) recSetInit;
    }
    

    Then it's easy to use IXMLSerializer to get XML:

    public static XElement StoreAsXml(IFeatureClass fc)
    {
        // Can't serialize a feature class directly, so convert
        //  to recordset first.
        IRecordSet2 recordset = ConvertToRecordset(fc);
    
        IXMLSerializer xmlSer = new XMLSerializerClass();
        string sXml = xmlSer.SaveToString(recordset, null, null);
    
        return XElement.Parse(sXml);           
    }
    

    However, when you convert to IRecordSet2, you lose the feature class name, so when writing to a file, I add an element to the XML to hold the feature class name:

    public static void StoreToFile(IFeatureClass fc, string filePath)
    {
        XElement xdoc = StoreAsXml(fc);
    
        XElement el = new XElement("FeatureClass", new XAttribute( "name", fc.AliasName ),
                                    xdoc);
    
        el.Save(filePath);
    }
    

    Now, just reverse the process to read the XML into a feature class. Remember that an element was added to store the feature class name:

    public static IFeatureClass RetreiveFromFile(string filepath)
    {
        XElement xdoc = XElement.Load(filepath);
        string sName = xdoc.FirstAttribute.Value;
        XNode recordset = xdoc.FirstNode;
    
        return RetreiveFromXml(recordset, sName);
    }
    

    Simple de-serialization using IXMLSerializer to get a IRecordSet2:

    public static IFeatureClass RetreiveFromXml(XNode node, string sName)
    {
        IXMLSerializer xmlDeSer = new XMLSerializerClass();
        IRecordSet2 recordset = (IRecordSet2)xmlDeSer.LoadFromString(node.ToString(), null, null);
    
        return ConvertToFeatureClass(recordset, sName);
    }
    

    This was the tricky part. I'm open to suggestions on how to improve this ... covert the IRecordSet2 object into an IFeatureClass:

    private static IFeatureClass ConvertToFeatureClass(IRecordSet2 rs, string sName)
    {
        IWorkspaceFactory pWSFact = new ShapefileWorkspaceFactory();
    
        string sTempPath = Path.GetTempPath();
        IFeatureWorkspace pFWS = (IFeatureWorkspace)pWSFact.OpenFromFile( sTempPath, 0);
    
        // Will fail (COM E_FAIL) if the dataset already exists
        DeleteExistingDataset(pFWS, sName);
    
        IFeatureClass pFeatClass = null;
        pFeatClass = pFWS.CreateFeatureClass(sName, rs.Fields, null, null, esriFeatureType.esriFTSimple,
                                             "SHAPE", "");
    
        // Copy incoming record set table to new feature class's table
        ITable table = (ITable) pFeatClass;
        table = rs.Table;
    
        IFeatureClass result = table as IFeatureClass;
    
        // It will probably work OK without this, but it makes the XML match more closely
        IClassSchemaEdit3 schema = result as IClassSchemaEdit3;
        schema.AlterAliasName(sName);
        schema.AlterFieldAliasName("FID", "");
        schema.AlterFieldModelName("FID", "");
        schema.AlterFieldAliasName("Shape", "");
        schema.AlterFieldModelName("Shape", "");
    
        // If individual fields need to be edited, do something like this:
        //      int nFieldIndex = result.Fields.FindField("Shape");
        //      IFieldEdit2 field = (IFieldEdit2)result.Fields.get_Field(nFieldIndex);
    
        // Cleanup 
        DeleteExistingDataset(pFWS, sName);
    
        return table as IFeatureClass;
    }
    

    Finally, a utility method for deleting an existing dataset. This was copy/pasted from somewhere, but I can't remember the source.

    public static void DeleteExistingDataset(IFeatureWorkspace pFWS, string sDatasetName)
    {
        IWorkspace pWS = (IWorkspace)pFWS;
        IEnumDatasetName pEDSN = pWS.get_DatasetNames(esriDatasetType.esriDTFeatureClass);
        bool bDatasetExists = false;
        pEDSN.Reset();
        IDatasetName pDSN = pEDSN.Next();
        while (pDSN != null)
        {
            if (pDSN.Name == sDatasetName)
            {
                bDatasetExists = true;
                break;
            }
            pDSN = pEDSN.Next();
        }
        if (bDatasetExists)
        {
            IFeatureClass pFC = pFWS.OpenFeatureClass(sDatasetName);
            IDataset pDataset = (IDataset)pFC;
            pDataset.Delete();
        }
    }