c #databound ComboBox：InvalidArgument =值'1'对'SelectedIndex'无效

Question

I'm having problems setting the SelectedIndex on a bound ComboBox (on a windows form) that I'm adding to a form at runtime and I suspect there's something odd going on.

When I try this, I get the error "InvalidArgument=Value of '1' is not valid for 'SelectedIndex'."

private void Form1_Load(object sender, EventArgs e)
        {
            List<string> comboBoxList = new List<string>();
            comboBoxList.Add("Apples");
            comboBoxList.Add("Oranges");
            comboBoxList.Add("Pears");

            ComboBox comboBox1 = new ComboBox();
            comboBox1.DataSource = comboBoxList;
            comboBox1.SelectedIndex = 1;
            this.Controls.Add(comboBox1);
        }

However, there is no problem if I add the items to the ComboBox directly, like this:

comboBox1.Add("Apples");

Also, there is no problem if I add the control to the form BEFORE I set the SelectedIndex, like this:

ComboBox comboBox1 = new ComboBox();
this.Controls.Add(comboBox1);
comboBox1.DataSource = comboBoxList;
comboBox1.SelectedIndex = 1;

Can anyone explain why I can't set the selected index from a datasource until after the control is added to the form?

Answer 1

My understanding is that the databinding is handled by the bindingcontext normaly this is the parent forms bindingcontext. So the datasource binding does not happen until you add the comboBox to the form. You can also get this to work if you set the comboBox's bindingcontext to the forms binding context.

comboBox1.BindingContext = this.BindingContext;
comboBox1.DataSource = comboBoxList;
comboBox1.SelectedIndex = 1;
this.Controls.Add(comboBox1);

BindingContext Class

What is BindingContext