Label TextProperty CoerceValue delegate not called - xamarin.forms

Question

I use Reflection to set the Label.TextProperty.CoerceValue to my custom delegate (TextProperty.CoerceValue are null by default)
but when Label text changed, the delegate are not called
the same strategy are apply/tried on Image.SourceProperty, Entry.TextProperty
all are called successful
is bug or Label.TextProperty by design will not call CoerceValue delegate?
thank you very much.
Xamarin.Forms 4.3.0.947036
var property = Label.TextProperty;
var coerceValue = property.GetType().GetProperty("CoerceValue", BindingFlags.NonPublic | BindingFlags.Instance);
oldDelegate = coerceValue?.GetValue(property) as BindableProperty.CoerceValueDelegate;
coerceValue?.SetValue(property, (bindable, value) => {
var modified = ModifyValue(value); // simply modify the value if required
return modified
});

Answer 1

If you want to call CoerceValue when Label.Text changed, I suggest you can use Bindable Properties to bind Label.TextPrperty.
public partial class Page9 : ContentPage
{
public static readonly BindableProperty labelvalueProperty = BindableProperty.Create("labelvalue", typeof(string), typeof(Page9), null , coerceValue: CoerceValue);
public string labelvalue
{
get { return (string)GetValue(labelvalueProperty); }
set { SetValue(labelvalueProperty, value); }
}
private static object CoerceValue(BindableObject bindable, object value)
{
string str = (string)value;
if(str=="cherry")
{
str = "hello world!";
}
return str;
}
public Page9 ()
{
InitializeComponent ();
label1.SetBinding(Label.TextProperty, "labelvalue");
labelvalue = "this is test";
BindingContext = this;
}
private void Btn1_Clicked(object sender, EventArgs e)
{
labelvalue = "cherry";
}
}
You can see the CoerceValue can be fired when Label.Text property changed.

Answer 2

I created a new Page Page1 in a Xamarin.Forms Project, with the following simple code in the code behind:
public Page1()
{
InitializeComponent();
}
protected override void OnAppearing()
{
Label l = new Label();
BindableProperty.CoerceValueDelegate d = (s, a) =>
{
string modified = "textY"; // simply modify the value if required
return modified;
};
var property = Label.TextProperty;
var coerceValue = property.GetType().GetProperty("CoerceValue", BindingFlags.NonPublic | BindingFlags.Instance);
var oldDelegate = coerceValue?.GetValue(property) as BindableProperty.CoerceValueDelegate;
coerceValue?.SetValue(property, d);
l.Text = "1"; // Text property is set to textY thanks to CoerceValueDelegate!
base.OnAppearing();
}
when i call l.Text = "1" the BindableProperty.CoerceValueDelegate i defined is correctly called, and l.Text is set to textY as expected.
#codetale, are you able to run this code on your side?