void SetupUserInterface()
        {
            activity = this.Context as Activity;
            view     = activity.LayoutInflater.Inflate(Resource.Layout.ViewerLayout, this, false);

            mPdfViewCtrl = view.FindViewById <pdftron.PDF.PDFViewCtrl>(Resource.Id.pdfviewctrl);
            AppUtils.SetupPDFViewCtrl(mPdfViewCtrl, PDFViewCtrlConfig.GetDefaultConfig(this.Context));

            var file = Utils.CopyResourceToLocal(this.Context, Resource.Raw.sample, "sample", ".pdf");

            mPdfDoc = mPdfViewCtrl.OpenPDFUri(Android.Net.Uri.FromFile(file), "");

            FragmentActivity fragmentActivity = null;

            if (activity is FragmentActivity)
            {
                fragmentActivity = activity as FragmentActivity;
            }
            mToolManager = ToolManagerBuilder.From().Build(fragmentActivity, mPdfViewCtrl);
            mToolManager.SetCanOpenEditToolbarFromPan(true);
            mToolManager.OpenEditToolbar += (sender, e) =>
            {
                mAnnotationToolbar.Show(AnnotationToolbar.StartModeEditToolbar, null, 0, e.Mode, !mAnnotationToolbar.IsShowing);
            };

            mAnnotationToolbar = view.FindViewById <AnnotationToolbar>(Resource.Id.annotationtoolbar);
            mAnnotationToolbar.Setup(mToolManager);
            mAnnotationToolbar.SetButtonStayDown(true);
            mAnnotationToolbar.HideButton(AnnotationToolbarButtonId.Close);
            mAnnotationToolbar.Show();

            mSeekBar = view.FindViewById <ThumbnailSlider>(Resource.Id.thumbseekbar);
        }
        protected override void OnDetachedFromWindow()
        {
            base.OnDetachedFromWindow();

            mSeekBar?.ClearResources();
            mSeekBar = null;

            mPdfViewCtrl?.Destroy();
            mPdfViewCtrl = null;
            mPdfDoc?.Close();
            mPdfDoc = null;
        }