protected override void OnDetachedFromWindow()
        {
            base.OnDetachedFromWindow();

            mPdfViewCtrl?.Destroy();
            mPdfViewCtrl = null;
            mPdfDoc?.Close();
            mPdfDoc = null;
        }
        protected override void OnDetachedFromWindow()
        {
            base.OnDetachedFromWindow();

            mSeekBar?.ClearResources();
            mSeekBar = null;

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