CSV Export - How to handle file-in-use error

[Tim]

I wrote a CSV export event handler for a RadGridView based on this example:

http://demos.telerik.com/silverlight/#GridView/ExportingPagedData

private void ExportCSV(object sender, RoutedEventArgs e)
{
    SaveFileDialog dialog = new SaveFileDialog
                                {DefaultExt = ".csv", Filter = "CSV Files|*.csv|All Files|*.*", FilterIndex = 1};

    bool? result = dialog.ShowDialog();

    if (result == true)
    {
        int originalPageSize = EventDataPager.PageSize;
        int originalPageIndex = EventDataPager.PageIndex;
        EventDataPager.PageSize = 0;

        try
        {
            using (Stream stream = dialog.OpenFile())
            {
                EventViewerGridView.Export(stream, GridViewExportOptions);
            }
        }
        catch(IOException ioe)
        {
            RadWindow.Alert(ioe.Message);
        }

        EventDataPager.PageSize = originalPageSize;
        EventDataPager.PageIndex = originalPageIndex;
    }
}

If the saved file is open by Excel already, then the dialog.OpenFile() call throws an IOException.  I display this to the user with a RadWindow.Alert() from the catch(IOException...) block, however, I subsequently get the following exception:

Error: An unknown error has occurred.
Detail: System.InvalidOperationException
This operation can only occur on the UI Thread.
   at System.Windows.Hosting.NativeHost.VerifyThread()
   at System.Windows.SaveFileStream.Dispose(Boolean disposing)
   at System.IO.FileStream.Finalize()


I can't check stream.CanWrite because it does not get past the OpenFile() call. 
I put the RadWindow.Alert() on the Dispatcher as a test without any apparent effect.

How can I handle this properly without generating this subsequent error?

Thanks,
Tim

[Veselin Vasilev]

Hi Tim,

Have you tried replacing the RadWindow.Alert with MessageBox.Show?
It fixes the problem in 99% of the cases. Can you please try?

This is something not directly connected to RadGridView. You can reproduce it with any open file if you try to open it again.

Greetings,
Veselin Vasilev
the Telerik team

[Tim]

Thanks for the reply.  MessageBox.Show() fails in exactly the same way, and it doesn't look like the rest of my app either ;)

Tim

[Veselin Vasilev]

Hello Tim,

To my regret I am not aware of any solution to this general problem so far.

Best wishes,
Veselin Vasilev
the Telerik team

[David]

This is an issue with the Silverlight runtime. I ran into this problem as well, and I implemented the workaround suggested here:

http://forums.silverlight.net/forums/t/176869.aspx

The workaround is to explicitly ignore that particular unhandled exception in App.xaml.cs.

[Kevin]

In the 2011.1.419.1040 release, I can't even get the IOException to be thrown anymore. Was there a change made in the Telerik code to automatically suppress this error?

I execute the code below, which trys to save a RadGrid export to an .xml file, which I have open in Excel, and I don't get any errors.  Additionally, the .xml file is not updated!  This is a problem, since users may think are getting new data in their .xml file, but are not.  The save should return an IOException, "The process cannot access the file '<FileName>' because it is being used by another process".  I could then tell the user the file was not updated.

I am in big trouble the first time a user makes a critical business decision using old data, just because they had the file open in Excel when they tried to export and I couldn't prompt them.

private void Button_Click(object sender, RoutedEventArgs e)
{
    string extension = "xml";
    ExportFormat format = ExportFormat.ExcelML;
    SaveFileDialog dialog = new SaveFileDialog()
    {
        DefaultExt = extension,
        Filter = String.Format("Excel XML files (*.{0})|*.{0}|All files (*.*)|*.*", extension),
        FilterIndex = 1
    };
    if (dialog.ShowDialog() == true)
    {
        using (Stream stream = dialog.OpenFile())
        {
            Grid.Export(stream,
                new GridViewExportOptions()
                {
                    Format = format,
                    ShowColumnHeaders = true,
                    ShowColumnFooters = true,
                    ShowGroupFooters = true,
                });
        }
    }
}

[Vlad]

Hello,

How we can change a code which is not part of our assemblies? The grid export method will use just a stream - it is up to developer to handle the code with SaveFileDialog.

Best wishes,
Vlad
the Telerik team