c#の入力ボックス関数

private static string InputBox(string Caption, string Hint, string Default)
        {
            Form InputForm = new Form();
            InputForm.MinimizeBox = false;
            InputForm.MaximizeBox = false;
            InputForm.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog;
            InputForm.StartPosition = FormStartPosition.CenterScreen;
            InputForm.Width = 220;
            InputForm.Height = 150;

            InputForm.Text = Caption;
            Label lbl = new Label();
            lbl.Text = Hint;
            lbl.Left = 10;
            lbl.Top = 20;
            lbl.Parent = InputForm;
            lbl.AutoSize = true;
            TextBox tb = new TextBox();
            tb.Left = 30;
            tb.Top = 45;
            tb.Width = 160;
            tb.Parent = InputForm;
            tb.Text = Default;
            tb.SelectAll();
            Button btnok = new Button();
            btnok.Left = 30;
            btnok.Top = 80;
            btnok.Parent = InputForm;
            btnok.Text = " ";
            InputForm.AcceptButton = btnok;// 

            btnok.DialogResult = DialogResult.OK;
            Button btncancal = new Button();
            btncancal.Left = 120;
            btncancal.Top = 80;
            btncancal.Parent = InputForm;
            btncancal.Text = " ";
            btncancal.DialogResult = DialogResult.Cancel;
            try
            {
                if (InputForm.ShowDialog() == DialogResult.OK)
                {
                    return tb.Text;
                }
                else
                {
                    return null;
                }
            }
            finally
            {
                InputForm.Dispose();
            }
        }