Question

I have the following sample where the SourceData class would represent a DataView resulting from an Sql query:

class MainClass
{
    private static SourceData Source;
    private static DataView View;
    private static DataView Destination;
        
    public static void Main (string[] args)
    {
        Source = new SourceData();
        View = new DataView(Source.Table);
        Destination = new DataView();
            
        Source.AddRowData("Table1", 100);
        Source.AddRowData("Table2", 1500);
        Source.AddRowData("Table3", 1300324);
        Source.AddRowData("Table4", 1122494);
        Source.AddRowData("Table5", 132545);

        Console.WriteLine(String.Format("Data View Records: {0}", View.Count));         

        foreach(DataRowView drvRow in View)
        {
            Console.WriteLine(String.Format("Source {0} has {1} records.", drvRow["table"], drvRow["records"]));
            DataRowView newRow = Destination.AddNew();
            newRow["table"] = drvRow["table"];
            newRow["records"] = drvRow["records"];
        }
            
        Console.WriteLine();
        Console.WriteLine(String.Format("Destination View Records: {0}", Destination.Count));
            
        foreach(DataRowView drvRow in Destination)
        {
            Console.WriteLine(String.Format("Destination {0} has {1} records.", drvRow["table"], drvRow["records"]));
        }

    }
}

class SourceData
{
    public DataTable Table
    {
        get{return dataTable;}
    }
        
    private DataTable dataTable;
    
    public SourceData()
    {
        dataTable = new DataTable("TestTable");
        dataTable.Columns.Add("table", typeof(string));
        dataTable.Columns.Add("records", typeof(int));
    }
        
    public void AddRowData(string tableName, int tableRows)
    {
        dataTable.Rows.Add(tableName, tableRows);
    }
}

My output is:

Data View Records: 5
Source Table1 has 100 records.

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object at System.Data.DataView.AddNew () [0x0003e] in /usr/src/packages/BUILD/mono-2.4.2.3
/mcs/class/System.Data/System.Data/DataView.cs:344 at DataViewTest.MainClass.Main (System.String[] args) [0x000e8] in /home/david/Projects/DataViewTest/SourceData.cs:29

I did some reading here: DataView:AddNew Method…
…and it would appear that I am doing this the right way. How come I am getting the Object reference not set?

Answer 1

The DataView has to be a view of something. The way you’ve got it, it’s not a view of anything (using the default constructor) – you need to at least set the DataView.Table property to something.

I think you actually want to create a new DataTable for “destination”, not a DataView.