C＃组合框下拉列表项类型

Question

I have a form with sixteen combo-boxes, each with the DropDownStyle property set to DropDownList . I am trying to set the form so each control shows its first pre-defined value:

    private void Form1_Load(object sender, EventArgs e)
    {
        foreach (ComboBox DropDown in this.Controls.OfType<ComboBox>())
            DropDown.SelectedIndex = 0;
    }

This code is not working, although individually assigning each item does. Any ideas why?

Answer 1

My WinForm experience is a bit rusty, but if I remember correctly, this.Controls will only bring you those controls directly under the main Form. If you have any subcontrols, like a Groupbox, they will be under that groupbox's . Controls .

You can either explicitly iterate your Groupbox's controls, or you can use recursion to go over all child controls of the form, like you can see here .

Answer 2

You have to detect the control and its type for ComboBox... This means you have to deal with nested loop to detect the controls

foreach (Control MyCtrl in this.Controls)
{
    DoAllRichTextBoxes(MyCtrl);
}

void DoAllRichTextBoxes(Control control)
{
    ComboBox Cmb = control as ComboBox;
    TextBox TxtBx = control as TextBox;
    if (Cmb == null && TxtBx == null)
    {
        // deal with nested controls
        foreach (Control c in control.Controls) DoAllRichTextBoxes(c);
    }
    if (Cmb != null)
    {
        Cmb.GotFocus += new EventHandler(this.Tb_GotFocus);
        Cmb.LostFocus += new EventHandler(this.Tb_LostFocus);
        Cmb.KeyDown += new KeyEventHandler(this.VehComn_KeyDown);
        Cmb.SelectedValueChanged += new EventHandler(this.AllCombos_SelectedValueChanged);
    }
    if (TxtBx != null)
    {
        TxtBx.GotFocus += new EventHandler(this.Tb_GotFocus);
        TxtBx.LostFocus += new EventHandler(this.Tb_LostFocus);
        TxtBx.KeyPress += new KeyPressEventHandler(this.TbCmb_KeyPress);
        TxtBx.KeyDown += new KeyEventHandler(this.VehComn_KeyDown);
    }
}