C# Null reference exception when using a void function

Question

I'm sure I've got something wrong here but nobody in my team can explain what it is. My goal is to be able to populate a listView item from a button click in another form however a null reference exception is thrown when passing the variables to form1 (System.NullReferenceException: 'Object reference not set to an instance of an object.')

here is my code: Form1:

    AddRec addRec = new AddRec();
    public AddRec AddRec { get; set; }
    public static string viewItem1, viewItem2, viewItem3 = "";

    public void YesClick()
    {
        ListViewItem lvi = new ListViewItem(viewItem1);
        lvi.SubItems.Add(viewItem2);
        lvi.SubItems.Add(viewItem3);
        listView1.Items.Add(lvi);
    }

Form2(AddRec):

    private void btnAdd_Click(object sender, EventArgs e)
    {
        name = txtNameF.Text.ToLower() + " " + txtNameS.Text.ToLower();
        if (name != "")
        {
            num = txtNum.Text;
            mobileNum = txtModNo.Text;

            Form1.viewItem1 = name;
            Form1.viewItem2 = num;
            Form1.viewItem3 = mobileNum;
            Form1.YesClick();

            txtNameF.Text = "";
            txtNameS.Text = "";
            txtNum.Text = "";
            txtModNo.Text = "";
        }
        else
        {
            MessageBox.Show("Fields Required", "Warning");
        }
    }

The idea is that the add button on AddRec populates a listView in Form1 with the text from text boxes in AddRec. The exception is thrown on the Form1.YesClick()

Well, `YesClick()` is not a static method and needs `Form1` object reference! `viewItem1` etc are static and come with the class memory. So, to answer, just make `YesClick()` static and it will work. — praty, Oct 13 '17 at 09:36
Not quite clear from you code but, `ListViewItem` has a `Subitems` collection check if this is null rather than adding to it directly ( `lvi.SubItems.Add(viewItem2);`) — Milen, Oct 13 '17 at 09:37
Changing the YesClick() function to static makes listView1 unreadable to the function so cannot add to the listview. Any additional info is very much appreciated :) — Jake Doe, Oct 13 '17 at 10:31

Willy David Jr · Accepted Answer · 2017-10-13T14:31:43.073

0

You cannot call Form1 like that. You need to call the "opened Form1" before populating or changing it's properties. Try this:

Form1 frm = Application.OpenForms.OfType<Form1>().Take(1).FirstOrDefault();
if (frm != null)
{
  //Populate all your properties here:
  frm.viewItem1 = name;
}

edited Oct 13 '17 at 14:31

answered Oct 13 '17 at 09:36

Willy David Jr

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Is there a library you are using in this example? my IDE doesn't recognize the keyword Application – Jake Doe Oct 13 '17 at 13:36
Are you using WinForm? – Willy David Jr Oct 13 '17 at 14:09
Make sure you are using this: using System.Windows.Forms; – Willy David Jr Oct 13 '17 at 14:10
I am using this library however copy pasting your code into my project, 'Application' is still not recognized – Jake Doe Oct 13 '17 at 14:26
I corrected my code. That should work fine now. – Willy David Jr Oct 13 '17 at 14:31
Let me know if it works now. – Willy David Jr Oct 13 '17 at 14:32
Works a treat :) thank you very much. the current form check has helped tons in different areas. Sidenot: I had to give the namespace for a windows forms application since I was using Microsoft Excel objects but your code runs perfect. – Jake Doe Oct 17 '17 at 09:16
You are welcome, glad to help :) – Willy David Jr Oct 17 '17 at 09:18

C# Null reference exception when using a void function

1 Answers1