Bind to property in custom control - xamarin.forms

Question

I have a custom control CustomTextBox.xaml:
<AbsoluteLayout xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MyApp.Core.Controls.CustomTextBox"
xmlns:controls="clr-namespace:MyApp.Core.Controls;assembly=MyApp.Core"
BackgroundColor="White">
<AbsoluteLayout.GestureRecognizers>
<TapGestureRecognizer Tapped="OnTapped"/>
</AbsoluteLayout.GestureRecognizers>
<Entry x:Name="textValueEntry" AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0.5, 1, 0.9, 0.9" FontAttributes="Bold"/>
<Label x:Name="placeholderLabel" AbsoluteLayout.LayoutFlags="PositionProportional" AbsoluteLayout.LayoutBounds="0.05, 0.5" FontSize="18"/>
</AbsoluteLayout>
I want to be able to bind to the textValueEntry control from the parent view. So I added a bindable property in CustomTextBox.xaml.cs:
private string _textValue;
public string TextValue
{
get
{
return _textValue;
}
set
{
_textValue = value;
}
}
public static BindableProperty TextValueProperty = BindableProperty.Create(nameof(TextValue), typeof(string), typeof(CustomTextBox), string.Empty, BindingMode.TwoWay, null,
(bindable, oldValue, newValue) =>
{
(bindable as CustomTextBox).textValueEntry.Text = (string)newValue;
});
I try to bind to it from the parent view like this:
<controls:CustomTextBox HorizontalOptions="FillAndExpand" VerticalOptions="CenterAndExpand" HeightRequest="50" TextValue="{Binding UsernamePropertyInViewModel, Mode=TwoWay}"/>
TextValue property gets set with UsernamePropertyInViewModel when I launch the app, as I can see it in textValueEntry. But when I change the text in textValueEntry it doesn't update UsernamePropertyInViewModel. How can I bind to it so it updates UsernamePropertyInViewModel when I change the text in textValueEntry?

Answer 1

As far as I can tell your CustomTextBox entry textValueEntry doesn't Bind to your TextValue property.
Also your TextValue property needs to look like this for BindableProperties. You need to set your BindableProperty to the appropriate value for a Binding. No need for a private backing variable to TextValue.
public string TextValue
{
get => (string)GetValue(TextValueProperty);
set => SetValue(TextValueProperty, value);
}
Parent.Xaml
<Entry x:Name="textValueEntry" Text="{Binding Path=TextValue, Source={x:Reference Page}}" AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0.5, 1, 0.9, 0.9" FontAttributes="Bold"/>
Your Page will need an x:Name="Page" for the Binding Source