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using System;
using System.ComponentModel;
using System.Linq.Expressions;
using System.Reflection;
using System.Runtime.CompilerServices;
using DotNetDesignPatternDemos.Annotations;
namespace DotNetDesignPatternDemos.Behavioral.Observer.Bidirectional
{
public class Product : INotifyPropertyChanged
{
private string name;
public string Name
{
get => name;
set
{
if (value == name) return; // critical
name = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged(
[CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this,
new PropertyChangedEventArgs(propertyName));
}
public override string ToString()
{
return $"Product: {Name}";
}
}
public class Window : INotifyPropertyChanged
{
private string productName;
public string ProductName
{
get => productName;
set
{
if (value == productName) return; // critical
productName = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged(
[CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this,
new PropertyChangedEventArgs(propertyName));
}
public override string ToString()
{
return $"Window: {ProductName}";
}
}
public sealed class BidirectionalBinding : IDisposable
{
private bool disposed;
public BidirectionalBinding(
INotifyPropertyChanged first,
Expression<Func<object>> firstProperty,
INotifyPropertyChanged second,
Expression<Func<object>> secondProperty)
{
if (firstProperty.Body is MemberExpression firstExpr
&& secondProperty.Body is MemberExpression secondExpr)
{
if (firstExpr.Member is PropertyInfo firstProp
&& secondExpr.Member is PropertyInfo secondProp)
{
first.PropertyChanged += (sender, args) =>
{
if (!disposed)
{
secondProp.SetValue(second, firstProp.GetValue(first));
}
};
second.PropertyChanged += (sender, args) =>
{
if (!disposed)
{
firstProp.SetValue(first, secondProp.GetValue(second));
}
};
}
}
}
public void Dispose()
{
disposed = true;
}
}
public class Program
{
public static void Main(string[] args)
{
var product = new Product{Name="Book"};
var window = new Window{ProductName = "Book"};
// want to ensure that when product name changes
// in one component, it also changes in another
product.PropertyChanged += (sender, eventArgs) =>
{
if (eventArgs.PropertyName == "Name")
{
Console.WriteLine("Name changed in Product");
window.ProductName = product.Name;
}
};
window.PropertyChanged += (sender, eventArgs) =>
{
if (eventArgs.PropertyName == "ProductName")
{
Console.WriteLine("Name changed in Window");
product.Name = window.ProductName;
}
};
using var binding = new BidirectionalBinding(
product,
() => product.Name,
window,
() => window.ProductName);
// there is no infinite loop because of
// self-assignment guard
product.Name = "Table";
window.ProductName = "Chair";
Console.WriteLine(product);
Console.WriteLine(window);
}
}
}
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