Make the selected text of a listbox the text inside a textbox

Do you know how to make the selected text of a listbox the text inside a textbox?

I tried this but its not working:

Code:

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string[] details = { listBox4.SelectedItem.ToString() };
 textBox5.Text = details[0];

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Are you handling the SelectedIndex changed event?

What happens when you set a break point on the following line

Code:

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textBox5.Text = details[0];

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and inspect the details variable in the watch window (or by hovering over it)?