//遍历窗体所有控件，
foreach (Control control in this.Controls)
{
    //遍历后的操作...
    control.Enabled = false;
}

foreach (Control control in this.Controls)
{
　　//遍历所有TextBox...
    if (control is TextBox)
    {
        TextBox t = (TextBox)control;
        t.Enabled = false;
    }
　　//遍历所有DateTimePicker...
    if (control is DateTimePicker)
    {
        DateTimePicker d = (DateTimePicker)control;
        d.Enabled = false;
    }
}