C# xmlAttribute.Value Object reference not set to an instance of an object

Question

Good morning.

Shortly.

Using XmlDocument I'm programmaticaly creating document, which needs to look like this (sample):

<report>
    <header version="1" reportDate="2013-08-27" salesDate="2013-08-26"/>
    <data>
        <companies>
            <company id="ABCD">
                <customers>
                    <customer id="100000" storeId="AA"/>
                    <customer id="100001" storeId="AB"/>
                    <customer id="100002" storeId="AC"/>
                </customers>
            </company>
        </companies>
    </data>
</report>

I need to grab the data from a few DataGridView's so the foreach loops are intensively in use.

Which I can't work out nor to find the answer (always something about reading the XML, no creating) is why the code shown below throws me:

Object reference not set to an instance of an object

This is a sample of code I use:

[...]

XmlNode customersNode = doc.CreateElement("customers");
companyNode.AppendChild(customersNode);

XmlNode customerNode;
XmlAttribute customerAttribute;

foreach (DataGridViewRow row in dgvCustomers.Rows)
{
    customerNode = doc.CreateElement("customer");

    customerAttribute = doc.CreateAttribute("id");
    customerAttribute.Value = row.Cells[0].Value.ToString();
    //
    // __HERE__ is the problem (or a line above)
    //
    customerNode.Attributes.Append(customerAttribute);

    customerAttribute = doc.CreateAttribute("storeId");
    customerAttribute.Value = row.Cells[1].Value.ToString();
    customerNode.Attributes.Append(customerAttribute);

    customersNode.AppendChild(customerNode);
}

[...and so on...]

Also

customerNode.Attributes.Append(customerAttribute);

underlined (VS2010 editor) with this tip:

Possible 'System.NullReferenceException'

but I assume this is a reason of the problem described above?

Any support is appreciated and many thanks in advance for your time and knowledge share.

Best regards!

Are you sure that the row.Cells[0]has a value (is not nul) ? check with debug — Joan Caron
– Joan Caron, Commented Aug 30, 2013 at 9:47

Marc Gravell · Accepted Answer · 2013-08-30 09:49:19Z

1

I haven't tried running the code shown, but : you might find that simplifying it makes it harder to get wrong:

XmlElement customerNode; // <==== note this is XmlElement, not XmlNode
XmlAttribute customerAttribute;

foreach (DataGridViewRow row in dgvCustomers.Rows)
{
    customerNode = doc.CreateElement("customer");
    customerNode.SetAttribute("id", row.Cells[0].Value.ToString());
    customerNode.SetAttribute("storeId", row.Cells[1].Value.ToString());

    customersNode.AppendChild(customerNode);
}

You might also want to check that the issue isn't actually that row.Cells[0].Value.ToString() or row.Cells[1].Value.ToString() is throwing an exception.

answered Aug 30, 2013 at 9:49

Marc Gravell

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1 Comment

Partyz Kaft Over a year ago

OK, got it, method loading data to DGV's adds empty row below last data-containing row. It throws an exception :) Added check, works like a charm, thank You all!

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