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// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
using System.Collections.Generic;
namespace System.Reactive
{
/// <summary>
/// Base class for classes that expose an observable sequence as a well-known event pattern (sender, event arguments).
/// Contains functionality to maintain a map of event handler delegates to observable sequence subscriptions. Subclasses
/// should only add an event with custom add and remove methods calling into the base class's operations.
/// </summary>
/// <typeparam name="TSender">The type of the sender that raises the event.</typeparam>
/// <typeparam name="TEventArgs">The type of the event data generated by the event.</typeparam>
public abstract class EventPatternSourceBase<TSender, TEventArgs>
#if !NO_EVENTARGS_CONSTRAINT
where TEventArgs : EventArgs
#endif
{
private readonly IObservable<EventPattern<TSender, TEventArgs>> _source;
private readonly Dictionary<Delegate, Stack<IDisposable>> _subscriptions;
private readonly Action<Action<TSender, TEventArgs>, /*object,*/ EventPattern<TSender, TEventArgs>> _invokeHandler;
/// <summary>
/// Creates a new event pattern source.
/// </summary>
/// <param name="source">Source sequence to expose as an event.</param>
/// <param name="invokeHandler">Delegate used to invoke the event for each element of the sequence.</param>
/// <exception cref="ArgumentNullException"><paramref name="source"/> or <paramref name="invokeHandler"/> is null.</exception>
protected EventPatternSourceBase(IObservable<EventPattern<TSender, TEventArgs>> source, Action<Action<TSender, TEventArgs>, /*object,*/ EventPattern<TSender, TEventArgs>> invokeHandler)
{
if (source == null)
throw new ArgumentNullException("source");
if (invokeHandler == null)
throw new ArgumentNullException("invokeHandler");
_source = source;
_invokeHandler = invokeHandler;
_subscriptions = new Dictionary<Delegate, Stack<IDisposable>>();
}
/// <summary>
/// Adds the specified event handler, causing a subscription to the underlying source.
/// </summary>
/// <param name="handler">Event handler to add. The same delegate should be passed to the Remove operation in order to remove the event handler.</param>
/// <param name="invoke">Invocation delegate to raise the event in the derived class.</param>
/// <exception cref="ArgumentNullException"><paramref name="handler"/> or <paramref name="invoke"/> is null.</exception>
protected void Add(Delegate handler, Action<TSender, TEventArgs> invoke)
{
if (handler == null)
throw new ArgumentNullException("handler");
if (invoke == null)
throw new ArgumentNullException("invoke");
var gate = new object();
var isAdded = false;
var isDone = false;
var remove = new Action(() =>
{
lock (gate)
{
if (isAdded)
Remove(handler);
else
isDone = true;
}
});
//
// [OK] Use of unsafe Subscribe: non-pretentious wrapper of an observable in an event; exceptions can occur during +=.
//
var d = _source.Subscribe/*Unsafe*/(
x => _invokeHandler(invoke, /*this,*/ x),
ex => { remove(); ex.Throw(); },
() => remove()
);
lock (gate)
{
if (!isDone)
{
Add(handler, d);
isAdded = true;
}
}
}
private void Add(Delegate handler, IDisposable disposable)
{
lock (_subscriptions)
{
var l = new Stack<IDisposable>();
if (!_subscriptions.TryGetValue(handler, out l))
_subscriptions[handler] = l = new Stack<IDisposable>();
l.Push(disposable);
}
}
/// <summary>
/// Removes the specified event handler, causing a disposal of the corresponding subscription to the underlying source that was created during the Add operation.
/// </summary>
/// <param name="handler">Event handler to remove. This should be the same delegate as one that was passed to the Add operation.</param>
/// <exception cref="ArgumentNullException"><paramref name="handler"/> is null.</exception>
protected void Remove(Delegate handler)
{
if (handler == null)
throw new ArgumentNullException("handler");
var d = default(IDisposable);
lock (_subscriptions)
{
var l = new Stack<IDisposable>();
if (_subscriptions.TryGetValue(handler, out l))
{
d = l.Pop();
if (l.Count == 0)
_subscriptions.Remove(handler);
}
}
if (d != null)
d.Dispose();
}
}
}
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