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I'm making a simple Contact Manager as a practice project based on a XML file everything is working just fine except for two problems

Every time I click on the white blank space on ListBox, I get this exception:

Object reference not set to an instance of an object.

It doesn't happen if an item is selected on the ListBox though.

Code:

private void lstbox1_SelectedIndexChanged(object sender, EventArgs e)
{
    btnDelete.Enabled = true;

    if (rBtn1.Checked)
    {
        string xpath = "/Contacts/Contact[FullName='" + lstbox1.Text + "']";
        XmlNode node = doc.SelectSingleNode(xpath);

        txt2.Text = node["FullName"].InnerText; //This is where i get the exception
        txt3.Text = node["HomePhone1"].InnerText;
        txt4.Text = node["HomePhone2"].InnerText;
        txt5.Text = node["MobilePhone1"].InnerText;
        txt6.Text = node["MobilePhone2"].InnerText;
        txt7.Text = node["HomeAddress"].InnerText;
        txt8.Text = node["E-MailAddress"].InnerText;
    }

}

Also if someone can tell me how to search in a XML file through a TextBox that would be great. I tried Google but not much results about that.

Screenshot:

screenshot

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I would also recommend to ensure that you trim your input, and make sure that case of your search string matches – Roma Apr 27 at 2:45

closed as off topic by unholysampler, Jesse C. Slicer, MichaelT, Rein Henrichs, delnan Apr 27 at 8:36

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1 Answer

up vote 2 down vote

I bet node is null because your xpath query isn't returning any results.

Adding a null reference check should take care of your problem.

private void lstbox1_SelectedIndexChanged(object sender, EventArgs e)
{
    btnDelete.Enabled = true;

    if (rBtn1.Checked)
    {
        string xpath = "/Contacts/Contact[FullName='" + lstbox1.Text + "']";
        XmlNode node = doc.SelectSingleNode(xpath);

        if( node != null ) 
        {
           txt2.Text = node["FullName"].InnerText; //This is where i get the exception
           txt3.Text = node["HomePhone1"].InnerText;
           txt4.Text = node["HomePhone2"].InnerText;
           txt5.Text = node["MobilePhone1"].InnerText;
           txt6.Text = node["MobilePhone2"].InnerText;
           txt7.Text = node["HomeAddress"].InnerText;
           txt8.Text = node["E-MailAddress"].InnerText;
        }
    }
}
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