NullReferenceException occurs when adding new labels in panel

Question

I added a panel to Form1 component. That panel is named panel1.

When browsing a generic list, I want to add labels dynamically. Look to my little code:

if (list.Count > 0)
{

    foreach (TLClass item in list)
    {
        Label key = new Label();
        key.Text = item.Key;
        panel1.Container.Add(key);  //here throws an exception

        Label code = new Label();
        code.Text = item.Code.ToString();
        panel1.Container.Add(code);

        Label en = new Label();
        en.Text = item.Languages["EN-EN"].ToString();
        panel1.Container.Add(en);


        Label fr = new Label();
        fr.Text = item.Languages["FR-FR"].ToString();
        panel1.Container.Add(fr);

        Label nl = new Label();
        nl.Text = item.Languages["NL-NL"].ToString();
        panel1.Container.Add(nl);

        Label ro = new Label();
        ro.Text = item.Languages["RO-RO"].ToString();
        panel1.Container.Add(ro);

        Form1.ActiveForm.Container.Add(panel1);
    }
}

After line panel1.Container.Add(key);, immediately throws an exception NullReferenceException.

Why ? Where's my mistake ?

enter image description here

Problem solved I called with Controls instead of Container

Did you check whether panel1 is null? 99% likely it is, and the real question is "why?" — Eric J., Mar 11 '12 at 17:09
What event are you doing this in? Has the panel been sited (is panel1.Container null)? Please learn to use the debugger: you could very quickly determine what is null. — Jonathan Wood, Mar 11 '12 at 17:11
Also, unrelated, you don't have to check whether list.Count > 0. If it is zero, the foreach will return no enumerated objects. — Eric J., Mar 11 '12 at 17:12
Almost all cases of `NullReferenceException` are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, Oct 17 '13 at 03:10

score 4 · Accepted Answer · answered Mar 11 '12 at 17:15

4

You add controls to the container.
Which should be the parent form, but when you Add the parent form is not set.
However the right way is to add to the controls collection of the panel

panel1.Controls.Add(key);

answered Mar 11 '12 at 17:15

Steve

203,265
19
210
265

NullReferenceException occurs when adding new labels in panel

1 Answers1