/
MessageBus.cs
191 lines (168 loc) · 7.92 KB
/
MessageBus.cs
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
using System;
using System.Collections.Generic;
using System.Reactive.Concurrency;
using System.Reactive.Linq;
using System.Reactive.Subjects;
namespace ReactiveUI
{
/// <summary>
/// MessageBus represents an object that can act as a "Message Bus", a
/// simple way for ViewModels and other objects to communicate with each
/// other in a loosely coupled way.
///
/// Specifying which messages go where is done via a combination of the Type
/// of the message as well as an additional "Contract" parameter; this is a
/// unique string used to distinguish between messages of the same Type, and
/// is arbitrarily set by the client.
/// </summary>
public class MessageBus : IMessageBus
{
readonly Dictionary<Tuple<Type, string>, NotAWeakReference> messageBus =
new Dictionary<Tuple<Type, string>, NotAWeakReference>();
readonly IDictionary<Tuple<Type, string>, IScheduler> schedulerMappings =
new Dictionary<Tuple<Type, string>, IScheduler>();
/// <summary>
/// Registers a scheduler for the type, which may be specified at runtime, and the contract.
/// </summary>
/// <remarks>If a scheduler is already registered for the specified runtime and contract, this will overrwrite the existing registration.</remarks>
/// <typeparam name="T">The type of the message to listen to.</typeparam>
/// <param name="scheduler">The scheduler on which to post the
/// notifications for the specified type and contract. RxApp.DeferredScheduler by default.</param>
/// <param name="contract">A unique string to distinguish messages with
/// identical types (i.e. "MyCoolViewModel") - if the message type is
/// only used for one purpose, leave this as null.</param>
public void RegisterScheduler<T>(IScheduler scheduler, string contract = null)
{
schedulerMappings[new Tuple<Type, string>(typeof (T), contract)] = scheduler;
}
/// <summary>
/// Listen provides an Observable that will fire whenever a Message is
/// provided for this object via RegisterMessageSource or SendMessage.
/// </summary>
/// <typeparam name="T">The type of the message to listen to.</typeparam>
/// <param name="contract">A unique string to distinguish messages with
/// identical types (i.e. "MyCoolViewModel") - if the message type is
/// only used for one purpose, leave this as null.</param>
/// <returns>An Observable representing the notifications posted to the
/// message bus.</returns>
public IObservable<T> Listen<T>(string contract = null)
{
this.Log().Info("Listening to {0}:{1}", typeof (T), contract);
return SetupSubjectIfNecessary<T>(contract).Skip(1);
}
/// <summary>
/// Listen provides an Observable that will fire whenever a Message is
/// provided for this object via RegisterMessageSource or SendMessage.
/// </summary>
/// <typeparam name="T">The type of the message to listen to.</typeparam>
/// <param name="contract">A unique string to distinguish messages with
/// identical types (i.e. "MyCoolViewModel") - if the message type is
/// only used for one purpose, leave this as null.</param>
/// <returns>An Observable representing the notifications posted to the
/// message bus.</returns>
public IObservable<T> ListenIncludeLatest<T>(string contract = null)
{
this.Log().Info("Listening to {0}:{1}", typeof(T), contract);
return SetupSubjectIfNecessary<T>(contract);
}
/// <summary>
/// Determines if a particular message Type is registered.
/// </summary>
/// <param name="type">The Type of the message to listen to.</param>
/// <param name="contract">A unique string to distinguish messages with
/// identical types (i.e. "MyCoolViewModel") - if the message type is
/// only used for one purpose, leave this as null.</param>
/// <returns>True if messages have been posted for this message Type.</returns>
public bool IsRegistered(Type type, string contract = null)
{
bool ret = false;
WithMessageBus(type, contract, (mb, tuple) => { ret = mb.ContainsKey(tuple) && mb[tuple].IsAlive; });
return ret;
}
/// <summary>
/// Registers an Observable representing the stream of messages to send.
/// Another part of the code can then call Listen to retrieve this
/// Observable.
/// </summary>
/// <typeparam name="T">The type of the message to listen to.</typeparam>
/// <param name="source">An Observable that will be subscribed to, and a
/// message sent out for each value provided.</param>
/// <param name="contract">A unique string to distinguish messages with
/// identical types (i.e. "MyCoolViewModel") - if the message type is
/// only used for one purpose, leave this as null.</param>
public IDisposable RegisterMessageSource<T>(
IObservable<T> source,
string contract = null)
{
return source.Subscribe(SetupSubjectIfNecessary<T>(contract));
}
/// <summary>
/// Sends a single message using the specified Type and contract.
/// Consider using RegisterMessageSource instead if you will be sending
/// messages in response to other changes such as property changes
/// or events.
/// </summary>
/// <typeparam name="T">The type of the message to send.</typeparam>
/// <param name="message">The actual message to send</param>
/// <param name="contract">A unique string to distinguish messages with
/// identical types (i.e. "MyCoolViewModel") - if the message type is
/// only used for one purpose, leave this as null.</param>
public void SendMessage<T>(T message, string contract = null)
{
SetupSubjectIfNecessary<T>(contract).OnNext(message);
}
/// <summary>
/// Returns the Current MessageBus from the RxApp global object.
/// </summary>
public static IMessageBus Current
{
get { return RxApp.MessageBus; }
}
ISubject<T> SetupSubjectIfNecessary<T>(string contract)
{
ISubject<T> ret = null;
WithMessageBus(typeof (T), contract, (mb, tuple) => {
NotAWeakReference subjRef;
if (mb.TryGetValue(tuple, out subjRef) && subjRef.IsAlive) {
ret = (ISubject<T>)subjRef.Target;
return;
}
ret = new ScheduledSubject<T>(GetScheduler(tuple), null, new BehaviorSubject<T>(default(T)));
mb[tuple] = new NotAWeakReference(ret);
});
return ret;
}
void WithMessageBus(
Type type, string contract,
Action<Dictionary<Tuple<Type, string>, NotAWeakReference>,
Tuple<Type, string>> block)
{
lock (messageBus) {
var tuple = new Tuple<Type, String>(type, contract);
block(messageBus, tuple);
if (messageBus.ContainsKey(tuple) && !messageBus[tuple].IsAlive) {
messageBus.Remove(tuple);
}
}
}
IScheduler GetScheduler(Tuple<Type, string> tuple)
{
IScheduler scheduler;
schedulerMappings.TryGetValue(tuple, out scheduler);
return scheduler ?? RxApp.DeferredScheduler;
}
}
class NotAWeakReference
{
public NotAWeakReference(object target)
{
Target = target;
}
public object Target { get; private set; }
public bool IsAlive
{
get { return true; }
}
}
}
// vim: tw=120 ts=4 sw=4 et :