c# - ComboBox.SelectedValue is null in the Form's constructor

Question

I generated a very simple code snippet:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        dt = new DataTable();
        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("Title", typeof(string));
        dt.Rows.Add(1, "One");
        dt.Rows.Add(2, "Two");

        cmb = new ComboBox();
        cmb.DropDownStyle = ComboBoxStyle.DropDownList;
        cmb.DisplayMember = "Title";
        cmb.ValueMember = "ID";
        cmb.DataSource = dt;

        this.Controls.Add(cmb);
        cmb.SelectedValue = 2;
    }
}

When I set the value cmb.SelectedValue, SelectedValue is null.

I know that if I move this code to the Form1_Load handler, it will work as expected, but I need it in Form's Constructor.

Answer 1

You can call CreateControl() in the Form's Constructor to force the creation of the control's handle.

Forces the creation of the visible control, including the creation of the handle and any visible child controls.

The same effect can be achieved reading the Handle property:

The value of the Handle property is a Windows HWND. If the handle has not yet been created, referencing this property will force the handle to be created.

The SelectValue property will have value after this point.

public Form1()
{
    InitializeComponent();

    // [...]

    this.Controls.Add(cmb);

    cmb.CreateControl();
    cmb.SelectedValue = 2;
}