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NumericUpDown issues

Invalid cast exception when NumericUpDown text box is cleared​

When the text box of NumericUpDown is entirely cleared of input, the control may throw an invalid cast exception, e.g., Invalid cast from string to decimal?

To prevent these exceptions appearing, try the following:

  • Set TargetNullValue and FallbackValue on your Binding (both to 0). Ensure the values are explicitly typed to match the source property type (usually decimal or int) so they are treated as numbers rather than a string. This stops the empty text box from logging as a binding failure.
  • (Optional) Set UpdateSourceTrigger=LostFocus to stop the view model updating during edit states. This can reduce occurrences, but doesn't prevent them entirely.
<NumericUpDown Minimum="0" Maximum="10000000">
  <NumericUpDown.Value>
    <Binding Path="Units">
      <Binding.TargetNullValue><x:Decimal>0</x:Decimal></Binding.TargetNullValue>
      <Binding.FallbackValue><x:Decimal>0</x:Decimal></Binding.FallbackValue>
    </Binding>
  </NumericUpDown.Value>
</NumericUpDown>

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