PdfViewer Events
This article describes the Blazor PDF Viewer events and provides a runnable example with sample event handler implementations.
OnDownload
The OnDownload event fires when the user clicks on the Download button in the PDF Viewer toolbar.
The event handler receives an argument of type PdfViewerDownloadEventArgs. The event is cancellable and allows the application to set a name of the downloaded file. Do not add the .pdf file extension - the component will do that. The default name of the downloaded file is Document.pdf. See the example below.
OnError
The OnError event fires when a file error occurs. For example, the user tries to open a corrupt file or a file that is not in the correct format.
The event handler receives an argument of type PdfViewerErrorEventArgs, which exposes a Message property. See the example below.
OnOpen
The OnOpen event fires when the user selects a file to open from the PDF Viewer toolbar.
The event handler receives an argument of type PdfViewerOpenEventArgs. The event is cancellable and allows the application to obtain the PDF file name, size and contents as a Stream. To read the Stream, you may need to increase the maximum SignalR message size.
Using OnOpen is not required. Users can open local files from their devices without this handler. See the example below.
ZoomChanged
The ZoomChanged event fires when the user clicks on the zoom in/out buttons, or selects a new zoom level from the ComboBox.
The event handler receives the new zoom level as an argument of type decimal. To apply the new zoom level, set it as a new Zoom parameter value. Not setting it will effectively cancel the event.
Example
Handle or cancel Blazor PDF Viewer Events
<p> Last event: @EventLog </p>
<p><label> <TelerikCheckBox @bind-Value="@AllowDownloads" /> Allow Downloads </label></p>
<TelerikPdfViewer Data="@PdfSource"
Height="600px"
OnDownload="@OnPdfDownload"
OnError="@OnPdfError"
OnOpen="@OnPdfOpen"
Zoom="@PdfZoom"
ZoomChanged="@OnPdfZoomChanged">
</TelerikPdfViewer>
@code {
private byte[] PdfSource { get; set; }
private decimal PdfZoom { get; set; } = 1.25m;
private bool AllowDownloads { get; set; } = true;
private string EventLog { get; set; } = "...";
private async Task OnPdfDownload(PdfViewerDownloadEventArgs args)
{
if (AllowDownloads)
{
args.FileName = "PDF-Viewer-Download";
EventLog = $"Download {args.FileName}.pdf";
}
else
{
args.IsCancelled = true;
EventLog = $"Download cancelled";
}
}
private async Task OnPdfError(PdfViewerErrorEventArgs args)
{
// To trigger the event, rename a random file to error.pdf and try to open it.
EventLog = "Error: " + args.Message;
}
private async Task OnPdfOpen(PdfViewerOpenEventArgs args)
{
var file = args.Files.FirstOrDefault();
if (file.Size > 1024 * 1024)
{
args.IsCancelled = true;
EventLog = $"Open cancelled conditionally. File {file.Name} ({file.Size} bytes) is larger than 1 MB.";
}
else
{
// Get the PDF file contents if necessary.
var buffer = new byte[file.Stream.Length];
await file.Stream.ReadAsync(buffer);
EventLog = $"Open {file.Name}, {file.Size} bytes";
}
}
private async Task OnPdfZoomChanged(decimal newZoom)
{
PdfZoom = newZoom;
EventLog = "Zoom level changed.";
}
}