Consider restricting the user input for formulas by validating formulas before they're entered into the cell. This would prevent invalid formulas from being submitted in the first place.

It sounds like you're running into an issue where entering an invalid formula in the WPF XamSpreadSheet results in an endless error loop that prevents further work. To resolve this issue, you can consider the following strategies:

1. Handle Errors Programmatically

You can prevent the endless error dialogs by handling formula errors in your code. Use the FormulaError event to catch invalid formulas before they trigger an endless loop.

Example:

xamSpreadsheet.FormulaError += (sender, e) =>
{
    // Handle the formula error (e.g., display a custom error message)
    e.Cancel = true; // Prevent the default error dialog
};

This way, the FormulaError event can intercept any invalid formulas, and you can manage how the errors are handled instead of letting the default behavior take over.

2. Programmatically Remove the Invalid Formula

If you are stuck in the formula editor, you can clear the formula programmatically (without needing to interact with the UI) when such an error occurs.

Example:

// Assuming xamSpreadsheet is your XamSpreadSheet control
xamSpreadsheet.CurrentCell.Formula = ""; // Clear the formula programmatically

This clears the invalid formula and allows the user to continue working without being blocked by the error.

3. Restrict Formula Input

Consider restricting the user input for formulas by validating formulas before they're entered into the cell. This would prevent invalid formulas from being submitted in the first place.

Example:

xamSpreadsheet.EditingStarted += (sender, e) =>
{
    var formula = e.Cell.Formula;
    if (IsFormulaInvalid(formula)) // Define a method to check formula validity
    {
        // Handle invalid formula input
        e.Cancel = true; // Cancel the editing process
        MessageBox.Show("Invalid formula entered.");
    }
};

This will stop users from entering problematic formulas, avoiding the endless error loop.

4. Enable Formula Validation

If possible, implement more robust formula validation. Check the formula structure before it gets executed or rendered. This can prevent certain types of invalid inputs from being processed by the XamSpreadSheet.

5. Use Try-Catch for Error Handling

Another approach could be wrapping the formula evaluation logic in a try-catch block to handle any unexpected errors more gracefully. If the formula is invalid, you can catch the exception and handle it appropriately (e.g., by showing a custom error message and clearing the formula).

Example:

try
{
    // Formula evaluation logic
}
catch (Exception ex)
{
    // Handle the exception (e.g., clear the formula or show a message)
    xamSpreadsheet.CurrentCell.Formula = ""; // Clear the invalid formula
    MessageBox.Show("Error with the formula: " + ex.Message);
}

6. Reset Formula Using Keyboard Shortcuts

If the dialog is blocking the interface, try using the Esc key or Ctrl+Z (Undo) to cancel the operation and return the spreadsheet to a functional state.

7. Disable Error Dialogs Temporarily

If the error dialogs are becoming a problem, you can disable them in the settings for the XamSpreadSheet control and handle the errors programmatically as described above.

By implementing one or more of these solutions, you should be able to stop the endless loop of error dialogs and get back to working in the spreadsheet. Let me know if you need more detailed code examples or further assistance!

To test this scenario i use your excel sheet .BadFormula.xlsx and load it into XamSpreadsheet and not able to reproduce the behavior you described.

I attached my test sample here for your reference , if i am missing something please feel free to modify it and send me back for further investigation.

WpfApp14.zip

I just enter "=sum(1+...+50)" with no commas into excel I get #NAME? in the cell and i retain the ability to edit the formula.  In the XamSpreadSheet I get an error dialog which I can exit but when i click on the cell or the top bar to edit the formula to fix it I get the dialog again.  I can close it again but anything I do I always get the dialog again and again and again.  It happens with any bad formula, you can also use "=sum(" .BadFormula.xlsx

Hello,

Try to use the same formula to MS excel and test what is the behavior you are getting ? Is it different ?

Can you share your excel containing the formula so that i can try to load it into XamSpredSheet to test it or you can also share your own sample to investigation it .