C# Listbox Passing Strings

Question

I seem to have a problem passing some strings on from one form to another. I have two listBoxes on Form1 but i want to use Form2 to pass the information on into the listBoxes in Form1. In Form2 i have a button_Click function that calls a function in Form1 with params string a and string b.

private void button_Click(object sender, EventArgs e){
Form1 frm = new Form1();
frm.AddItemToListBox(txtBox1.Text,txtBox2.Text);
}

Below is the code to call the function AddItemToListBox in Form1.
Above is the function AddItemToListBox in Form1.

AddItemToListBox(string a, string b){
listBox1.Items.Add(a);
listBox2.Items.Add(b);
}

However this does not add the strings into the listboxes. There are no error messages or anything. I have also tried declaring 2 public strings STR1 and STR2

AddItemToListBox(string a, string b){
listBox1.Items.Add(a);
listBox2.Items.Add(b);
STR1 = a;
STR2 = b;
}

But if i used a button that displays STR1 and STR2's value. They will be "", String.Empty. Nothing shows up in the MessageBox that displays the value. However, if i place the MessageBox.Show(a); and MessageBox.Show(b); in the AddItemToListBox function, the strings will be correctly shown but still not added to the listbox.

This has been frustrating me for like 2 hours now and i want to find out why and how to actually use that method to add an item to a listbox if its possible. Greatest thanks in advance.

Steve · Accepted Answer · 2012-07-02 10:43:04Z

3

Try to add a frm.Show() at the end of this method.

private void button_Click(object sender, EventArgs e)
{ 
    Form1 frm = new Form1(); 
    frm.AddItemToListBox(txtBox1.Text,txtBox2.Text); 
    frm.Show();
}

But I'm sure that this doesn't solve your problem. Just show you that you need to reference the correct Form1. I think you are creating a new instance of Form1, yuo need to address the correct one

answered Jul 2, 2012 at 10:43

Steve

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1 Comment

woodmon122 Over a year ago

Thanks for the prompt reply. That worked. I understand it now.

James Osborn · Accepted Answer · 2012-07-02 10:43:58Z

1

Form1 frm = new Form1();

The above will initialize a new form, it will not change an existing instance of Form1.

answered Jul 2, 2012 at 10:43

James Osborn

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1 Comment

woodmon122 Over a year ago

Thanks. I understand it now. Is there a way to not initialize a new form? Like just calling from Form1

IvoTops · Accepted Answer · 2012-07-02 10:53:47Z

0

Either your inputs are empty, so debugwatch txtBox1.Text before calling

frm.AddItemToListBox(txtBox1.Text,txtBox2.Text);

Or the form does not redraw after adding your string. This can be forced by using

listBox1.Invalidate();
listBox2.Invalidate();

right after adding the strings

answered Jul 2, 2012 at 10:53

IvoTops

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