OpenTween.TweenMain.ShowSuplDialog C# (CSharp) Method

        public void ShowSuplDialog(TextBox owner, AtIdSupplement dialog, int offset, string startswith)
        {
            dialog.StartsWith = startswith;
            if (dialog.Visible)
            {
                dialog.Focus();
            }
            else
            {
                dialog.ShowDialog();
            }
            this.TopMost = this._cfgCommon.AlwaysTop;
            int selStart = owner.SelectionStart;
            string fHalf = "";
            string eHalf = "";
            if (dialog.DialogResult == DialogResult.OK)
            {
                if (!string.IsNullOrEmpty(dialog.inputText))
                {
                    if (selStart > 0)
                    {
                        fHalf = owner.Text.Substring(0, selStart - offset);
                    }
                    if (selStart < owner.Text.Length)
                    {
                        eHalf = owner.Text.Substring(selStart);
                    }
                    owner.Text = fHalf + dialog.inputText + eHalf;
                    owner.SelectionStart = selStart + dialog.inputText.Length;
                }
            }
            else
            {
                if (selStart > 0)
                {
                    fHalf = owner.Text.Substring(0, selStart);
                }
                if (selStart < owner.Text.Length)
                {
                    eHalf = owner.Text.Substring(selStart);
                }
                owner.Text = fHalf + eHalf;
                if (selStart > 0)
                {
                    owner.SelectionStart = selStart;
                }
            }
            owner.Focus();
        }

        private void FilterTextBox_KeyPress(object sender, KeyPressEventArgs e)
        {
            TweenMain main = (TweenMain)this.Owner;
            TextBox   tbox = (TextBox)sender;

            if (e.KeyChar == '@')
            {
                //if (!SettingDialog.UseAtIdSupplement) return;
                //@マーク
                main.ShowSuplDialog(tbox, main.AtIdSupl);
                e.Handled = true;
            }
            else if (e.KeyChar == '#')
            {
                //if (!SettingDialog.UseHashSupplement) return;
                main.ShowSuplDialog(tbox, main.HashSupl);
                e.Handled = true;
            }
        }