Question

I’m doing a winform which consist a listbox (listbox10) with some items on it. When I doubleclick an item, it will show another form (Form3) which consist a textbox (textbox1) and the textbox’s text is the item I select. Below is my coding.

Form3 msgForm3;
private void listBox10_DoubleClick(object sender, EventArgs e)
{

    msgForm3 = new Form3();
    textBox1.Text = listBox10.SelectedItem.ToString();
    msgForm3.Show();
}

But somehow I don’t know why, the textbox is always empty. Anything wrong with my coding?

Answer 1

The textBox1 you are accessing is not on msgForm3. to access the one on msgForm3 use (as the other answers have mentioned)

msgForm3.textBox1.Text = listBox10.SelectedItem.ToString(); 

but since all form controls are private by default you can either change its protection level inside Form3.Designer.cs to public (or internal ) :

public System.Windows.Forms.TextBox textBox1;

or add the text that should go in textbox1 as a parameter in Form3 constructor :

public Form3(string text)
{
    InitializeComponent();
    this.textBox1.Text = text;
}

and when your create an instance of Form3 use

msgForm3 = new Form3(listBox10.SelectedItem.ToString());