protected override void OnMouseClick(MouseEventArgs e) { base.OnMouseClick(e); bool isTrailingHit; bool isInside; HitTestMetrics hitTestMetrics = this._textLayout.HitTestPoint(e.X, e.Y, out isTrailingHit, out isInside); if (isInside) { bool underline = _textLayout.GetUnderline((int)hitTestMetrics.TextPosition); _textLayout.SetUnderline(!underline, new TextRange((int)hitTestMetrics.TextPosition, 1)); Render(); } }