Xamarin Forms how to add behaviors to custom control - xamarin.forms

Question

I have created a custom control,which is a ContentView with a Label and an Entry
The xaml of the custom controls looks like this:
<Label Text="{Binding Source={x:Reference ValidationControl}, Path=Caption}"/>
<Entry Text="{Binding Source={x:Reference ValidationControl}, Path=Value, Mode=TwoWay}" />
The code behind of the custom control looks like this:
public static readonly BindableProperty CaptionProperty = BindableProperty.Create(
nameof(Caption), typeof(string), typeof(ValidationEntry), default(string));
public string Caption
{
get => (string)GetValue(CaptionProperty);
set => SetValue(CaptionProperty, value);
}
public static readonly BindableProperty ValueProperty = BindableProperty.Create(
nameof(Value), typeof(string), typeof(ValidationEntry), default(string));
public string Value
{
get => (string)GetValue(ValueProperty);
set => SetValue(ValueProperty, value);
}
I’m using the custom control in the following way
<controls:ValidationEntry Caption=”Name:” Value="{Binding FullName, Mode=TwoWay}" />
My question is how to add behaviors to the custom control?
I would like to add them in the place that I’m using the control. i.e.
<controls:ValidationEntry Caption="Name:"
Value="{Binding FullName, Mode=TwoWay}">
<controls:ValidationEntry.EntryBehaviors>
<behaviors:EntryLengthValidatorBehavior IgnoreSpaces="True"/>
</controls:ValidationEntry.EntryBehaviors>
</controls:ValidationEntry>

Answer 1

You can create a behaviors directly, I add a NumericValidationBehavior in my custom entry to check the data if it is double.If type of the data is not double, the color of text will be set to red.
Here is xaml code.
<StackLayout>
<local:MyEntry local:NumericValidationBehavior.AttachBehavior="true">
</local:MyEntry>
</StackLayout>
Here is NumericValidationBehavior.cs
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;
}
}
Update
I create a custom view with ContentView
<ContentView xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="BeHavDemo.MyView">
<ContentView.Content>
<StackLayout>
<Label Text="xxxx"/>
<Entry Text="eeeee" />
</StackLayout>
</ContentView.Content>
</ContentView>
Then I create a behavior.
public class MyBeha : Behavior<MyView>
{
protected override void OnAttachedTo(BindableObject view)
{
base.OnAttachedTo(view);
var myview=view as MyView;
StackLayout stackLayout = (StackLayout)myview.Content;
Label label = (Label)stackLayout.Children[0];
Entry entry=(Entry) stackLayout.Children[1];
}
}