WPF Controls Visibility

Question

I'm new in WPF and I Want to hide/show some controls like TextBlock, ComboBox etc from code behind depending of a ComboBox Value. I've searched for some solutions without luck. I often the follow answer.

textbox1.Visibility = Visibility.Hidden;

So, I tried this one.

    private void cbBuscar_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        MessageBox.Show(cbBuscar.SelectedIndex.ToString());

        if (cbBuscar.SelectedIndex == 0)
        {
           cbProduto.Visibility = Visibility.Hidden;
        }
        else if (cbBuscar.SelectedIndex == 1)
        {
            cbProduto.Visibility = Visibility.Visible;
        }
        else if (cbBuscar.SelectedIndex == 2)
        {
            cbProduto.Visibility = Visibility.Collapsed;
        }
    }

It simple does not work. Trying that I get this error {"Object reference not set to an instance of an object."}

Do what I'm trying must not be hard, actually it must be pretty easy. Then, could anyone tell what I'm doing wrong?

Answer 1

Try placing the following code inside your cbBuscar_SelectionChanged function:

if (!IsLoaded)
    return;

If the selection is changing before the window initializes, this may fix the problem.

So your function would look like this:

private void cbBuscar_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    if (!IsLoaded)
        return;

    MessageBox.Show(cbBuscar.SelectedIndex.ToString());

    if (cbBuscar.SelectedIndex == 0)
    {
       cbProduto.Visibility = Visibility.Hidden;
    }
    else if (cbBuscar.SelectedIndex == 1)
    {
        cbProduto.Visibility = Visibility.Visible;
    }
    else if (cbBuscar.SelectedIndex == 2)
    {
        cbProduto.Visibility = Visibility.Collapsed;
    }
}