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How to store scrolled position and navigate to the scrolled position in PdfViewerControl
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While reopening the document in WPF PDFViewer, navigate the pdf document's scroll position to which the document was scrolled when the application was closed. The user should achieve this by adding the ScrollChanged and DocumentLoaded Events to the PdfViewerControl. Please find below the steps to store and navigate the scroll position using PdfViewerControl.
Step 1: Tracking the scroll position
- Wire the ScrollChanged event from PdfViewerControl.
C#
// Wire the PdfViewerControl ScrollChanged event pdfViewerControl.ScrollChanged += PdfViewerControl_ScrollChanged;
- Track the scroll position and store the current scroll points when the document gets scrolled.
C#
//Handle the ScrollChanged event
private void PdfViewerControl_ScrollChanged(object sender, System.Windows.Controls.ScrollChangedEventArgs args)
{
//To check if it is not initially scrolled values
if(!(args.VerticalOffset == 0 && args.HorizontalOffset != 0) && (args.VerticalOffset != 0 || args.HorizontalOffset != 0))
{
if (_savedPosition.ContainsKey(_fileNameWithPath))
{
//Remove the existing data for the same file name
_savedPosition.Remove(_fileNameWithPath);
}
//Add the Scroll positions in the dictionary
_savedPosition.Add(_fileNameWithPath, new DocPosition(pdfViewerControl.ZoomPercentage, args.HorizontalOffset, args.VerticalOffset));
}
}
Step 2:Store the scroll position
- Wire the Closed event from MainWindow.
C#
//Wire the MainWindow Closed event this.Closed += Window_Closed;
- Store the position points in a text file while closing the application.
C#
//Handle the Closed event
private void Window_Closed(object sender, EventArgs e)
{
//Clear all the data in the text file
System.IO.File.WriteAllText("../../Data/scrolledposition.txt", "");
foreach (var PositionValue in _savedPosition)
{
string filepath = PositionValue.Key;
DocPosition lastSavedPosition = PositionValue.Value;
//Add all the scroll data in the text file
System.IO.File.AppendAllText("../../Data/scrolledposition.txt", filepath + "," + lastSavedPosition.ZoomPercent + "," + lastSavedPosition.Horizontal.ToString() + "," + lastSavedPosition.Vertical.ToString()+ "\n");
}
}
Step 3: Retrieve scroll position
- Wire the Loaded event from MainWindow.
C#
//Wire the MainWindow Loaded event this.Loaded += MainWindow_Loaded;
- Retrieve the stored position data from the text file.
C#
//Handle the Loaded event
private void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
//Read all the text from the text file
string scrollPositions = System.IO.File.ReadAllText("../../Data/scrolledposition.txt");
//Check the text file is not empty or null
if (!scrollPositions.IsNullOrWhiteSpace() && scrollPositions != "")
{
string[] scrollInfo = scrollPositions.Split('\n');
foreach(string scrollInfo_Pdf in scrollInfo)
{
if(scrollInfo_Pdf != "")
{
string[] lastSavedValue = scrollInfo_Pdf.Split(',');
int zoomPercentage = Convert.ToInt32(lastSavedValue[1]);
double horizonalPosition = Convert.ToDouble(lastSavedValue[2]);
double verticalPostion = Convert.ToDouble(lastSavedValue[3]);
//Add the stored data to the dictionary
_savedPosition.Add(lastSavedValue[0], new DocPosition(zoomPercentage, horizonalPosition, verticalPostion));
}
}
}
}
Step 4: Navigate to scrolled position
- Wire the DocumentLoaded event from PdfViewerControl.
C#
//Wire the PdfViewerControl DocumentLoaded event pdfViewerControl.DocumentLoaded += PdfViewerControl_DocumentLoaded;
- Once the document is loaded, check if the pdf is already opened and stored scroll position or not, then navigate the pdf to the scroll positions using the “ScrollTo” method.
C#
//Handle DocumentLoaded event
private void PdfViewerControl_DocumentLoaded(object sender, System.EventArgs args)
{
//Check the file scroll positions in the text file
if (_savedPosition.ContainsKey(_fileNameWithPath))
{
_currentPosition = _savedPosition[_fileNameWithPath];
}
//Otherwise create default positions(0,0)
else
{
_currentPosition = new DocPosition(100,0,0);
_savedPosition.Add(_fileNameWithPath, _currentPosition);
}
//Zooming the pdf document based on the saved scroll position
pdfViewerControl.ZoomTo(_currentPosition.ZoomPercent);
//Calculate the offset based on the zoom value
double zoomfactor = (float)pdfViewerControl.ZoomPercentage / 100f;
//Scroll the pdf document based on the saved scroll position
pdfViewerControl.ScrollTo(_currentPosition.Horizontal/zoomfactor, _currentPosition.Vertical/zoomfactor);
}
