Steps to create a behavior (how create a behavior) - xamarin.forms

Question

i need to create a behavior from a view, i am using a class, also namespace to call to behavior but it's not working for me, i do not know what is my wrong, because i am doing all of step to create a behavior.
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Layouts.Commands.BasketView"
xmlns:local="clr-namespace:Layouts;assembly=Layouts"
Title="Cart">
<StackLayout Padding="10,60,10,0">
<Label Text="Red when the number isn't valid" FontSize="Small" />
<Entry Placeholder="Enter a System.Double"
local:NumericValidationBehavior.AttachBehavior="true" />
</StackLayout>
</ContentPage>
in this line i get the error local:NumericValidationBehavior.AttachBehavior="true" />
i have my behavior, but it cannot be instanciate in the view (see code up), there are other step to be instanciate?
namespace AttachedNumericValidationBehavior
{
public static class NumericValidationBehavior
{
public static readonly BindableProperty AttachBehaviorProperty
= BindableProperty.CreateAttached("AttachBehavior", typeof(bool), typeof(NumericValidationBehavior), false, propertyChanged: OnAttachBehaviorChanged);
public static bool GetAttachBehavior(BindableObject view)
{
return (bool)view.GetValue(AttachBehaviorProperty);
}
public static void SetAttachBehavior(BindableObject view, bool value)
{
view.SetValue(AttachBehaviorProperty, value);
}
static void OnAttachBehaviorChanged(BindableObject view, object oldValue, object newValue)
{
var entry = view as Entry;
if (entry == null)
{
return;
}
bool attachBehavior = (bool)newValue;
if (attachBehavior)
{
entry.TextChanged += OnEntryTextChanged;
}
else
{
entry.TextChanged -= OnEntryTextChanged;
}
}
static void OnEntryTextChanged(object sender, TextChangedEventArgs args)
{
double result;
bool isValid = double.TryParse(args.NewTextValue, out result);
((Entry)sender).TextColor = isValid ? Color.Default : Color.Red;
}
}
}
the error is: "AttachBehavior is not in type NumericValidationBehavior"

Answer 1

You class NumericValidationBehavior belongs to namespace AttachedNumericValidationBehavior, so when you want to use NumericValidationBehavior in xaml, the namespace local should be:
xmlns:local="clr-namespace:AttachedNumericValidationBehavior;"
And use the namespace:
<StackLayout Padding="10,60,10,0">
<Label Text="Red when the number isn't valid" FontSize="Small" />
<Entry Placeholder="Enter a System.Double"
local:NumericValidationBehavior.AttachBehavior="true" />
</StackLayout>
For more details, see document: Declaring Namespaces for Types