WPF/C#: How to make a selection from a listbox with one click?

Question

I have two listboxes with categories and subcategories. I would like subcategories popup when a category is clicked once.

Even though my code works with mouse double-click event, I couldn't work it out with one click. I tried mouse down, mouse up preview mouse down etc. They all give null reference error

    private void DataCategoryListBox_PMouseLDown(object sender, MouseButtonEventArgs e)
    {

        string selectedCat = DataCategoryListBox.SelectedItem.ToString();
        MessageBox.Show(selectedCat);

        if (selectedCat == "Geological")
        {
            string[] GeoCats = { "soil", "hydrogeology" };
            SubCatListBox.ItemsSource = GeoCats;
        }          
    }

Is there a solution to this?

Does this answer your question? [How to capture a mouse click on an Item in a ListBox in WPF?](https://stackoverflow.com/questions/1271375/how-to-capture-a-mouse-click-on-an-item-in-a-listbox-in-wpf) — IndieGameDev, Oct 06 '20 at 13:57
@MathewHD that solution may work also but it is a lot easier to use SelectionChanged in my case - Thanks anyway. — Amadeus, Oct 06 '20 at 14:17

score 1 · Accepted Answer · answered Oct 06 '20 at 14:07

You want to know when a category is selected, therefore you should use the SelectionChanged event. When you use MouseDown, there probably isn't anything selected yet, that's why you get the null exception:

private void DataCategoryListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    string selectedCat = DataCategoryListBox.SelectedItem.ToString();
    MessageBox.Show(selectedCat);

    if (selectedCat == "Geological")
    {
        string[] GeoCats = { "soil", "hydrogeology" };
        SubCatListBox.ItemsSource = GeoCats;
    }          
}

Yes, it worked. I thought SelectionChanged can be used after a selection is made. Thanks! — Amadeus, Oct 06 '20 at 14:15

WPF/C#: How to make a selection from a listbox with one click?

1 Answers1