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# control(_:didFailToValidatePartialString:errorDescription:)

Invoked when the formatter for the cell belonging to `control` (or selected cell) rejects a partial string a user is typing into the cell.

```
@MainActor optional func control(_ control: NSControl, didFailToValidatePartialString string: String, errorDescription error: String?)
```

## Parameters

`control`

The control whose cell rejected the string.

`string`

The string that includes the character that caused the rejection.

`error`

A localized, user-presentable string that explains why the string was rejected.

## Discussion

You can implement this method to display a warning message or perform a similar action when the user enters improperly formatted text.

## See Also

  <doc://com.apple.documentation/documentation/Foundation/Formatter/isPartialStringValid(_:newEditingString:errorDescription:)>


---

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