All 6 Forms, Input & Validation questions
More in Forms, Input & Validation
How do you build a data entry form in MAUI? How do you use Picker and BindablePicker for selections? How do you implement real-time field validation as the user types? How do you implement INotifyDataErrorInfo for robust validation? How do you manage focus and keyboard behavior in forms?
Advertisement
.NET MAUI › Forms, Input & Validation

What are Behaviors in MAUI and how do they help forms?

Intermediate

Answer

Behaviors attach reusable logic to a control without subclassing. Derive from Behavior<T>, override OnAttachedTo/OnDetachingFrom, and add event handlers or bindable properties. They're ideal for validation, input masking, or character limits applied declaratively across many controls.
public class MaxLengthBehavior : Behavior<Entry>
{
    public int MaxLength { get; set; }
    protected override void OnAttachedTo(Entry e) =>
        e.TextChanged += (s, a) => { if (e.Text?.Length > MaxLength)
            e.Text = e.Text[..MaxLength]; };
}
Real-world example A phone-number field enforces a maximum length with a reusable behavior applied in XAML.

Common follow-ups: How do you make a behavior configurable? | Behavior vs Trigger?

Behaviors Validation Forms Input & Validation
All 6 Forms, Input & Validation questions