Validation checks user-provided data against validity rules, informs users when entries are invalid, and prevents invalid data from being submitted. Rules can require a number within a range, an approved-list value, or a valid email address. section 11.1.2
Validating a custom stepper
A stock-count stepper can prevent values below zero and disable its add button when input is invalid. Add a visible warning Label for feedback, or use validation behaviors from the .NET MAUI Community Toolkit. Rejecting an invalid value without explaining why is input prevention, not complete validation. section 11.1.2
private void MinusButton_Clicked(object sender, EventArgs e)
{
if (Value > 0)
{
Value--;
ValueEntry.Text = Value.ToString();
}
}
Use the decrement guard as a concrete example of enforcing a lower-bound rule before changing control state. section 11.1.2
if (e.NewTextValue.StartsWith("-"))
{
ValueEntry.Text = Value.ToString();
return;
}
Use the text-entry guard as a concrete example of detecting a negative value and restoring the current valid value. section 11.1.2
