Xamarin, Bindable Property

Question

Dear all

 

It looks like I do misunderstand something in bindable properties. I would appreciate if somebody could explain me, how to do it correctly and why it works like that.

 

Why does the Binding on the "MeetingControl for "Meeting.Subject" not work?

 

GitHub Link: https://github.com/PatrickRainer/BindablePropertyExample

 

This is my Main Page:

<?xml version="1.0" encoding="utf-8"?>
<ContentPage x:Name="MyPage"
 xmlns="http://xamarin.com/schemas/2014/forms"
 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
 xmlns:local="clr-namespace:SimpleSfTimePicker"
 x:Class="SimpleSfTimePicker.MainPage"
 BindingContext="{x:Reference Name=MyPage}">
    <StackLayout BackgroundColor="LightCyan">
            <Entry Text="{Binding Meeting.Subject}"/>
            <local:MeetingControl x:Name="MeetingControl"
 Subject="{Binding Meeting.Subject}"/>
        </StackLayout>
</ContentPage>

This is the Code Behind (For ease I used no Vm):

public partial class MainPage {
  Meeting _meeting;

  public MainPage() {
    InitializeComponent();

    Meeting = new Meeting {
      Subject = "A Meeting",
    };
  }

  public Meeting Meeting {
    get =>_meeting;
    set {
      _meeting = value;
      OnPropertyChanged();
    }
  }
}

The Meeting:

public sealed class Meeting: INotifyPropertyChanged {
  string _subject;

  public string Subject {
    get =>_subject;
    set {
      if (value == _subject) return;
      _subject = value;
      OnPropertyChanged();
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;

  [NotifyPropertyChangedInvocator]
  void OnPropertyChanged([CallerMemberName] string propertyName = null) {
    PropertyChanged ? .Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
}

The Meeting Control Xaml:

<?xml version="1.0" encoding="utf-8"?>
<ContentView x:Name="MyContentView"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:til="clr-namespace:Syncfusion.XForms.TextInputLayout;assembly=Syncfusion.Core.XForms"
x:Class="SimpleSfTimePicker.MeetingControl"
BindingContext="{x:Reference MyContentView}">
<StackLayout>
<til:SfTextInputLayout
Hint="Subject">
<Entry x:Name="SubjectEntry"/>
</til:SfTextInputLayout>
</StackLayout>
</ContentView>

The MeetingControl Code Behind:

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class MeetingControl {
  public static readonly BindableProperty SubjectProperty = BindableProperty.Create(nameof(Subject), typeof(string), typeof(MeetingControl), "default", BindingMode.TwoWay, null, PropertyChanged);

  static void PropertyChanged(BindableObject bindable, object oldvalue, object newvalue) {
    var str = (string) newvalue;
    var control = (MeetingControl) bindable;
    control.SubjectEntry.Text = str;
  }

  public string Subject {
    get {
      return (string) GetValue(SubjectProperty);
    }
    set {
      SetValue(SubjectProperty, value);
    }
  }

  public MeetingControl() {
    InitializeComponent();
  }
}