Why .NET apps keep crashing on your Tablet PC – Tales from the Crypto

Why .NET apps keep crashing on your Tablet PC

I’ve been struggling with this issue for some time.

I have a small, simple .NET application I wrote in Visual C# a few months ago – I’ve tentatively titled it “iFetch”, because it fetches radio shows from the BBC iPlayer.

It really is very little more than a simple data grid view that displays the details of the shows and allows users to select them for downloading and later listening.

Despite that, I’ve had some terrible trouble with it. Sometimes it’ll work perfectly, other times it’ll just suddenly crash, and apparently without warning and for different reasons – sometimes when I click on a row, other times when I select to sort on a column heading.

The crash seems to be intermittent, but doesn’t reproduce on other computers; even computers of the same configuration.

For those who want technical details, here we go – the crash is a System.StackOverflowException error, and appears to be due to an unchecked infinite recursion in System.Windows.Forms.dll!System.Windows.Forms.DataGridViewRow.DataGridViewRowAccessibleObject.Bounds.get().

The clue here is that this is a “DataGridViewRowAccessibleObject” – not a mere DataGridViewRow. These “AccessibleObject” versions of common .NET components only come into existence and spread their effect when an “accessibility application” is active on the system. Apparently, in addition to text-to-speech readers, braille devices, etc, a Tablet – whether external like mine, or internal like those in a Tablet PC – classifies as an accessibility application.

That’s why this bug was intermittent for me – sometimes I had my external graphics tablet plugged in, other times I didn’t. To make matters worse, it seems to only trigger when one or more rows in the DataGrid are hidden.

If you get this error, first try checking to see if Microsoft have fixed the flaw – check for .NET service packs – and then, if there is no direct fix for the flaw, try either unplugging your tablet, if you can, or temporarily stop the Tablet PC Input Service, while running the program.

So far, I have received no feedback from Microsoft about when this will be fixed.

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