Question

I have a created a UserControl with a combobox in it. This combobox is populated from a xml, when this is not present, it is loaded from resource file.
It works fine in the program, but it can’t be displayed in designer – it says: “Object reference not set to an instance of an object.”

In the class responsible for loading the list from xml the null reference check is skipped for reasons beyond my understanding…

public SortedDictionary<string, string> Countries
{
    get
    {
        if (object.ReferenceEquals(countries, null))
        {
            GetCountryList();
        }
        return countries;
    }
}

Populating of the comboBox goes like this:

comboBoxCountry.DataSource = new BindingSource(Program.language.Countries, null);

Program.language is initialized in Program, but it does not help for the Designer.

The question is, how (when, at what event) should I populate the ComboBox (=load list from xml) to be able to display my control in designer.

Answer 1

If possible, you want to check for this.DesignMode and then simply not load the ComboBox at design-time.