The onbeforeunload event fires when the document is about to be unloaded. This event allows you to display a message in a confirmation dialog box to inform the user whether he/she wants to stay or leave the current page. DotNetBrowser API allows handling this dialog using DialogHandler API. By default, the dialog is displayed. Using your custom implementation of theDialogHandler, you can handle this dialog in your own way. For example, you can display your custom message dialog or suppress the dialog and don't allow unloading web page.
The following sample demonstrates how to handle the onbeforeunload dialog:
MainWindow.xaml
<Window x:Class="WPFDialogHandlerSample.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:wpf="clr-namespace:DotNetBrowser.WPF;assembly=DotNetBrowser" Title="MainWindow" Height="350" Width="525"> <Grid Name="mainLayout"> <wpf:WPFBrowserView Name="browserView"/> </Grid> </Window>
C#
MainWindow.xaml.cs
using System;
using System.Windows;
using System.Windows.Controls;
using DotNetBrowser;
using DotNetBrowser.WPF;
namespace WPFDialogHandlerSample
{
public partial class MainWindow : Window
{
public MainWindow()
{
// Initialize WPF Application UI.
InitializeComponent();
var defaultHandler = browserView.Browser.DialogHandler;
browserView.Browser.DialogHandler = new CustomDialogHandler(defaultHandler);
// Load HTML from string into BrowserView.
browserView.Browser.LoadHTML("<html><body onbeforeunload='return myFunction()'>" +
"<a href='http://www.google.com'>Click here to leave</a>" +
"<script>function myFunction() { return 'Leave this web page?'; }" +
"</script></body></html>");
}
}
public class CustomDialogHandler : DialogHandler
{
private DialogHandler defaultHandler;
public CustomDialogHandler(DialogHandler defaultHandler)
{
this.defaultHandler = defaultHandler;
}
public CloseStatus OnBeforeUnload(UnloadDialogParams parameters) {
CloseStatus returnValue = CloseStatus.CANCEL;
String title = "Confirm Navigation";
String message = parameters.Message;
MessageBoxResult result = MessageBox.Show(message, title, MessageBoxButton.YesNo, MessageBoxImage.Question);
if (result == MessageBoxResult.Yes)
{
returnValue = CloseStatus.OK;
}
return returnValue;
}
public void OnAlert(DialogParams parameters)
{
defaultHandler.OnAlert(parameters);
}
public CloseStatus OnConfirmation(DialogParams parameters)
{
return defaultHandler.OnConfirmation(parameters);
}
public CloseStatus OnFileChooser(FileChooserParams parameters)
{
return defaultHandler.OnFileChooser(parameters);
}
public CloseStatus OnPrompt(PromptDialogParams parameters)
{
return defaultHandler.OnPrompt(parameters);
}
public CloseStatus OnReloadPostData(ReloadPostDataParams parameters)
{
return defaultHandler.OnReloadPostData(parameters);
}
public CloseStatus OnColorChooser(ColorChooserParams parameters)
{
return defaultHandler.OnColorChooser(parameters);
}
public CloseStatus OnSelectCertificate(CertificatesDialogParams parameters)
{
return defaultHandler.OnSelectCertificate(parameters);
}
}
}VB.NET
MainWindow.xaml.vb
Imports DotNetBrowser
Namespace WPFDialogHandlerSample
Class MainWindow
Inherits Window
Sub New()
' Initialize WPF Application UI.
InitializeComponent()
Dim defaultHandler = browserView.Browser.DialogHandler
browserView.Browser.DialogHandler = new CustomDialogHandler(defaultHandler)
' Load HTML from string into BrowserView.
browserView.Browser.LoadHTML("<html><body onbeforeunload='return myFunction()'>" +
"<a href='http://www.google.com'>Click here to leave</a>" +
"<script>function myFunction() { return 'Leave this web page?'; }" +
"</script></body></html>")
End Sub
End Class
Friend Class CustomDialogHandler
Implements DialogHandler
Private defaultHandler As DialogHandler
Public Sub New(defaultHandler As DialogHandler)
Me.defaultHandler = defaultHandler
End Sub
Public Function OnBeforeUnload(parameters As UnloadDialogParams) As CloseStatus _
Implements DialogHandler.OnBeforeUnload
Dim returnValue As CloseStatus = CloseStatus.CANCEL
Dim title As String = "Confirm Navigation"
Dim message As String = parameters.Message
Dim result As MessageBoxResult = MessageBox.Show(message, title, MessageBoxButton.YesNo,
MessageBoxImage.Question)
If result = MessageBoxResult.Yes Then
returnValue = CloseStatus.OK
End If
return returnValue
End Function
Public Sub OnAlert(parameters As DialogParams) Implements DialogHandler.OnAlert
defaultHandler.OnAlert(parameters)
End Sub
Public Function OnColorChooser(parameters As ColorChooserParams) As CloseStatus _
Implements DialogHandler.OnColorChooser
return defaultHandler.OnColorChooser(parameters)
End Function
Public Function OnConfirmation(parameters As DialogParams) As CloseStatus _
Implements DialogHandler.OnConfirmation
return defaultHandler.OnConfirmation(parameters)
End Function
Public Function OnFileChooser(parameters As FileChooserParams) As CloseStatus _
Implements DialogHandler.OnFileChooser
return defaultHandler.OnFileChooser(parameters)
End Function
Public Function OnPrompt(parameters As PromptDialogParams) As CloseStatus Implements DialogHandler.OnPrompt
return defaultHandler.OnPrompt(parameters)
End Function
Public Function OnReloadPostData(parameters As ReloadPostDataParams) As CloseStatus _
Implements DialogHandler.OnReloadPostData
return defaultHandler.OnReloadPostData(parameters)
End Function
Public Function OnSelectCertificate(parameters As CertificatesDialogParams) As CloseStatus _
Implements DialogHandler.OnSelectCertificate
return defaultHandler.OnSelectCertificate(parameters)
End Function
End Class
End NamespaceStarting from DotNetBrowser 1.19 it is possible to prevent disposing of the Browser instance if the web page has the onbeforeunload event. For this purpose, it is necesary to execute Browser.Dispose(bool checkBeforeUnload) method with the flag true.
Note: this method should be executed in the non-UI thread. Otherwise, occurs the deadlock.
This code sample demonstrates how to use it with the FormClosing event:
C#
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
try
{
Task<bool> disposeTask = browserView.Browser.Dispose(true);
if (disposeTask.IsCompleted)
{
e.Cancel = !disposeTask.Result;
return;
}
e.Cancel = true;
disposeTask.ContinueWith(t =>
{
if (t.Result)
{
BeginInvoke((Action) (() =>
{
FormClosing -= Form1_FormClosing;
Close();
}));
}
});
}
catch (Exception exception)
{
Console.WriteLine(exception);
}
}VB.NET
Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As FormClosingEventArgs) Try Dim disposeTask As Task(Of Boolean) = browserView.Browser.Dispose(True) If disposeTask.IsCompleted Then e.Cancel = Not disposeTask.Result Return End If e.Cancel = True disposeTask.ContinueWith(Sub(t) If t.Result Then BeginInvoke(CType((Sub() RemoveHandler FormClosing, AddressOf Form1_FormClosing Close() End Sub), Action)) End If End Sub) Catch exception As Exception Console.WriteLine(exception) End Try End Sub