Question

I built a program, and i press a button, the program crashes.
Here is the button’s code:

            _alRecord.WriteXml(@".\alRecord.xml", XmlWriteMode.WriteSchema);

Debuging returned StackoverFlow(location is marked in a comment), Here is the whole code:

        private string alFile = @".\alRecord.xml";

    public DataTable alRecord;
    public DataTable _alRecord
    {
        get
        { //location of stackoverflow
            if (_alRecord == null)
            {
                alRecord = new DataTable();
                if (File.Exists(alFile))
                { _alRecord.ReadXml(alFile); }
                else
                { InitDataTable2(_alRecord); }
            }
            return _alRecord;
        }
    }

    private void InitDataTable2(DataTable table)
    {
        table.TableName = "AlTable";
        table.Columns.Add("ID", typeof(int));
        table.Columns.Add("sun", typeof(bool));
        table.Columns.Add("mon", typeof(bool));
        table.Columns.Add("tue", typeof(bool));
        table.Columns.Add("wed", typeof(bool));
        table.Columns.Add("thu", typeof(bool));
        table.Columns.Add("fri", typeof(bool));
        table.Columns.Add("sat", typeof(bool));
        table.Columns.Add("doors", typeof(string));
        table.Columns.Add("from1", typeof(DateTime));
        table.Columns.Add("to1", typeof(DateTime));
        table.Columns.Add("from2", typeof(DateTime));
        table.Columns.Add("to1", typeof(DateTime));
        for (int i = 0; i < 99; i++)
        {
            var row = alRecord.NewRow();
            row["ID"] = i;
            row["sun"] = false;
            row["mon"] = false;
            row["tue"] = false;
            row["wed"] = false;
            row["thu"] = false;
            row["fri"] = false;
            row["sat"] = false;
            row["doors"] = "";
            row["from1"] = "00:01";
            row["to1"] = "23:59";
            row["from2"] = "00:01";
            row["to2"] = "23:59";
            alRecord.Rows.Add(row);
        }
    }
    private void alSave_Click(object sender, EventArgs e)
    {
        _alRecord.WriteXml(@".\alRecord.xml", XmlWriteMode.WriteSchema);
    }

Answer 1

You are calling your property from inside the getter of your property:

public DataTable _alRecord
{
    get
    {
        if (_alRecord == null) // <= whoops

That causes an infinite recursion – calling the getter of the property to see if it returns null calls the getter of the property to see if it returns null calls the getter of the property…

@Dave makes a good point in the comments – in c# it is common to use a naming convention that your property is CasedLikeThis and the backing field (the field where the property actually stores its value is _namedLikeThis. It makes it easier to distinguish – you always know the _ means backing field, and vice versa.