问如何选择tabindex最低的控件？

EN

var firstControl = this.AllChildControls().OrderBy(m => m.TabIndex).First();
firstControl.Focus();

/// <summary>
/// Preforms a preorder iteration through all children of this control, recursively.
/// </summary>
/// <returns></returns>
public static IEnumerable<Control> AllChildControls(this Control control)
{
   foreach (Control child in control.Controls)
   {
        yield return child;
        foreach (var grandchild in child.AllChildControls())
            yield return grandchild;
    }
}