#859940 - Pastie

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/// <summary>
/// Manages weak references to <see cref="INotifyPropertyChanged"/> 
/// subscribers and provides a friendly interface for <see cref="INotifyPropertyChanged"/> 
/// implementors to expose typed event subscription without relying on 
/// property string names.
/// </summary>
/// <remarks>
/// This class never leaks references to subscribers. 
/// </remarks>
/// <typeparam name="TSource">The type of the property changed source.</typeparam>
public class PropertyChangeManager<TSource>
	where TSource : INotifyPropertyChanged
{
	private List<Subscription> subscriptions = new List<Subscription>();
	private TSource source;

	/// <summary>
	/// Initializes a new instance of the <see cref="PropertyChangeManager&lt;TSource&gt;"/> class.
	/// </summary>
	/// <param name="source">The property changed source.</param>
	public PropertyChangeManager(TSource source)
	{
		this.source = source;
	}

	/// <summary>
	/// Subscribes to changes in the property referenced in the given 
	/// <paramref name="propertyExpression"/> with the given 
	/// <paramref name="callbackAction"/> delegate.
	/// </summary>
	/// <param name="propertyExpression">A lambda expression that accesses a property, such as <c>x => x.Name</c> 
	/// (where the type of x is <typeparamref name="TSource"/>).</param>
	/// <param name="callbackAction">The callback action to invoke when the given property changes.</param>
	public IDisposable SubscribeChanged(Expression<Func<TSource, object>> propertyExpression, Action<TSource> callbackAction)
	{
		return AddSubscription(new Subscription
		{
			IsStatic = callbackAction.Target == null,
			PropertyName = Reflect<TSource>.GetProperty(propertyExpression).Name,
			SubscriberReference = new WeakReference(callbackAction.Target),
			MethodCallback = callbackAction.Method
		});
	}

	/// <summary>
	/// Registers a regular event handler for change notification.
	/// </summary>
	public IDisposable AddHandler(PropertyChangedEventHandler handler)
	{
		return AddSubscription(new Subscription
		{
			IsStatic = handler.Target == null,
			SubscriberReference = new WeakReference(handler.Target),
			MethodCallback = handler.Method
		});
	}

	/// <summary>
	/// Unregisters the given event handler from change notification.
	/// </summary>
	/// <param name="handler">The value.</param>
	public void RemoveHandler(PropertyChangedEventHandler handler)
	{
		CleanupSubscribers();

		subscriptions.RemoveAll(s => s.SubscriberReference.Target == handler.Target && s.MethodCallback == handler.Method);
	}

	/// <summary>
	/// Notifies subscribers that the given property has changed.
	/// </summary>
	/// <param name="propertyExpression">A lambda expression that accesses a property, such as <c>x => x.Name</c> 
	/// (where the type of x is <typeparamref name="TSource"/>).</param>
	public void NotifyChanged(Expression<Func<TSource, object>> propertyExpression)
	{
		CleanupSubscribers();

		var propertyName = Reflect<TSource>.GetProperty(propertyExpression).Name;

		foreach (var subscription in subscriptions.Where(s => s.PropertyName == propertyName))
		{
			try
			{
				subscription.MethodCallback.Invoke(subscription.SubscriberReference.Target, new object[] { this.source });
			}
			catch (TargetInvocationException tie)
			{
				tie.InnerException.RethrowWithNoStackTraceLoss();
			}
		}

		// Call "old-style" handlers with the right signature.
		foreach (var subscription in subscriptions.Where(s => s.PropertyName == null))
		{
			try
			{
				subscription.MethodCallback.Invoke(subscription.SubscriberReference.Target, new object[] { this.source, new PropertyChangedEventArgs(propertyName) });
			}
			catch (TargetInvocationException tie)
			{
				tie.InnerException.RethrowWithNoStackTraceLoss();
			}
		}
	}

	private IDisposable AddSubscription(Subscription subscription)
	{
		CleanupSubscribers();

		subscriptions.Add(subscription);

		return new SubscriptionReference(this.subscriptions, subscription);
	}

	private void CleanupSubscribers()
	{
		subscriptions.RemoveAll(s => !s.IsStatic && !s.SubscriberReference.IsAlive);
	}

	/// <summary>
	/// Provides deterministic removal of a subscription without having to 
	/// create a separate class to hold the delegate reference. 
	/// Callers can simply keep the returned disposable from Subscribe 
	/// and use it to unsubscribe.
	/// </summary>
	private sealed class SubscriptionReference : IDisposable
	{
		private List<Subscription> subscriptions;
		private Subscription entry;

		public SubscriptionReference(List<Subscription> subscriptions, Subscription entry)
		{
			this.subscriptions = subscriptions;
			this.entry = entry;
		}

		public void Dispose()
		{
			this.subscriptions.Remove(this.entry);
		}
	}

	private class Subscription
	{
		public bool IsStatic { get; set; }
		public string PropertyName { get; set; }
		public WeakReference SubscriberReference { get; set; }
		public MethodInfo MethodCallback { get; set; }
	}
}

#region Helpers

/// <summary>
/// Provides strong-typed reflection of the <typeparamref name="TTarget"/> 
/// type.
/// </summary>
/// <typeparam name="TTarget">Type to reflect.</typeparam>
internal static class Reflect<TTarget>
{
	/// <summary>
	/// Gets the method represented by the lambda expression.
	/// </summary>
	/// <param name="method">An expression that invokes a method.</param>
	/// <exception cref="ArgumentNullException">The <paramref name="method"/> is null.</exception>
	/// <exception cref="ArgumentException">The <paramref name="method"/> is not a lambda expression or it does not represent a method invocation.</exception>
	/// <returns>The method info.</returns>
	public static MethodInfo GetMethod(Expression<Action<TTarget>> method)
	{
		return GetMethodInfo(method);
	}

	/// <summary>
	/// Gets the method represented by the lambda expression.
	/// </summary>
	/// <param name="method">An expression that invokes a method.</param>
	/// <typeparam name="T1">Type of the first argument.</typeparam>
	/// <exception cref="ArgumentNullException">The <paramref name="method"/> is null.</exception>
	/// <exception cref="ArgumentException">The <paramref name="method"/> is not a lambda expression or it does not represent a method invocation.</exception>
	/// <returns>The method info.</returns>
	public static MethodInfo GetMethod<T1>(Expression<Action<TTarget, T1>> method)
	{
		return GetMethodInfo(method);
	}

	/// <summary>
	/// Gets the method represented by the lambda expression.
	/// </summary>
	/// <param name="method">An expression that invokes a method.</param>
	/// <typeparam name="T1">Type of the first argument.</typeparam>
	/// <typeparam name="T2">Type of the second argument.</typeparam>
	/// <exception cref="ArgumentNullException">The <paramref name="method"/> is null.</exception>
	/// <exception cref="ArgumentException">The <paramref name="method"/> is not a lambda expression or it does not represent a method invocation.</exception>
	/// <returns>The method info.</returns>
	public static MethodInfo GetMethod<T1, T2>(Expression<Action<TTarget, T1, T2>> method)
	{
		return GetMethodInfo(method);
	}

	/// <summary>
	/// Gets the method represented by the lambda expression.
	/// </summary>
	/// <param name="method">An expression that invokes a method.</param>
	/// <typeparam name="T1">Type of the first argument.</typeparam>
	/// <typeparam name="T2">Type of the second argument.</typeparam>
	/// <typeparam name="T3">Type of the third argument.</typeparam>
	/// <exception cref="ArgumentNullException">The <paramref name="method"/> is null.</exception>
	/// <exception cref="ArgumentException">The <paramref name="method"/> is not a lambda expression or it does not represent a method invocation.</exception>
	/// <returns>The method info.</returns>
	public static MethodInfo GetMethod<T1, T2, T3>(Expression<Action<TTarget, T1, T2, T3>> method)
	{
		return GetMethodInfo(method);
	}

	/// <summary>
	/// Gets the property represented by the lambda expression.
	/// </summary>
	/// <param name="property">An expression that accesses a property.</param>
	/// <exception cref="ArgumentNullException">The <paramref name="method"/> is null.</exception>
	/// <exception cref="ArgumentException">The <paramref name="method"/> is not a lambda expression or it does not represent a property access.</exception>
	/// <returns>The property info.</returns>
	public static PropertyInfo GetProperty(Expression<Func<TTarget, object>> property)
	{
		PropertyInfo info = GetMemberInfo(property) as PropertyInfo;
		if (info == null)
		{
			throw new ArgumentException("Member is not a property");
		}

		return info;
	}

	/// <summary>
	/// Gets the field represented by the lambda expression.
	/// </summary>
	/// <param name="field">An expression that accesses a field.</param>
	/// <exception cref="ArgumentNullException">The <paramref name="method"/> is null.</exception>
	/// <exception cref="ArgumentException">The <paramref name="method"/> is not a lambda expression or it does not represent a field access.</exception>
	/// <returns>The field info.</returns>
	public static FieldInfo GetField(Expression<Func<TTarget, object>> field)
	{
		FieldInfo info = GetMemberInfo(field) as FieldInfo;
		if (info == null)
		{
			throw new ArgumentException("Member is not a field");
		}

		return info;
	}

	private static MethodInfo GetMethodInfo(Expression method)
	{
		if (method == null)
		{
			throw new ArgumentNullException("method");
		}

		LambdaExpression lambda = method as LambdaExpression;
		if (lambda == null)
		{
			throw new ArgumentException("Not a lambda expression", "method");
		}

		if (lambda.Body.NodeType != ExpressionType.Call)
		{
			throw new ArgumentException("Not a method call", "method");
		}

		return ((MethodCallExpression)lambda.Body).Method;
	}

	private static MemberInfo GetMemberInfo(Expression member)
	{
		if (member == null)
		{
			throw new ArgumentNullException("member");
		}

		LambdaExpression lambda = member as LambdaExpression;
		if (lambda == null)
		{
			throw new ArgumentException("Not a lambda expression", "member");
		}

		MemberExpression memberExpr = null;

		// The Func<TTarget, object> we use returns an object, so first statement can be either 
		// a cast (if the field/property does not return an object) or the direct member access.
		if (lambda.Body.NodeType == ExpressionType.Convert)
		{
			// The cast is an unary expression, where the operand is the 
			// actual member access expression.
			memberExpr = ((UnaryExpression)lambda.Body).Operand as MemberExpression;
		}
		else if (lambda.Body.NodeType == ExpressionType.MemberAccess)
		{
			memberExpr = lambda.Body as MemberExpression;
		}

		if (memberExpr == null)
		{
			throw new ArgumentException("Not a member access", "member");
		}

		return memberExpr.Member;
	}
}

/// <summary>
/// Utility methods for exceptions.
/// </summary>
public static class ExceptionExtensions
{
	private static readonly FieldInfo remoteStackTraceString =
		typeof(Exception).GetField("_remoteStackTraceString", BindingFlags.Instance | BindingFlags.NonPublic) ??
		typeof(Exception).GetField("remote_stack_trace", BindingFlags.Instance | BindingFlags.NonPublic);

	/// <summary>
	/// Rethrows an exception object without losing the existing stack trace information.
	/// </summary>
	/// <param name="ex">The exception to re-throw.</param>
	/// <remarks>
	/// For more information on this technique, see
	/// http://www.dotnetjunkies.com/WebLog/chris.taylor/archive/2004/03/03/8353.aspx
	/// </remarks>
	public static void RethrowWithNoStackTraceLoss(this Exception ex)
	{
		remoteStackTraceString.SetValue(ex, ex.StackTrace + Environment.NewLine);

		throw ex;
	}
}

#endregion