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Now we need to subscribe to those events. So let s create a couple of classes to simulate what the production department would need to do (see Example 5-22).

Value of A: 10

class ProductionDeptTool1 { public void Subscribe ( DocumentProcessor processor ) { processor.Processing += processor_Processing; processor.Processed += processor_Processed; } public void Unsubscribe(DocumentProcessor processor) { processor.Processing -= processor_Processing; processor.Processed -= processor_Processed; } void processor_Processing(object sender, EventArgs e) { Console.WriteLine("Tool1 has seen processing."); } void processor_Processed(object sender, EventArgs e) { Console.WriteLine("Tool1 has seen that processing is complete."); }

}

class ProductionDeptTool2 { public void Subscribe( DocumentProcessor processor ) { processor.Processing += (sender, e) => Console.WriteLine("Tool2 has seen processing."); processor.Processed += (sender, e) => Console.WriteLine("Tool2 has seen that processing is complete."); } }

To subscribe to an event we use the += operator, with a suitable delegate. You can see in ProductionDeptTool1.Subscribe that we used the standard delegate syntax, and in ProductionDeptTool2.Subscribe we used the lambda expression syntax.

The types of class members that can be declared static are shown checked in Table 6-2. The other member types cannot be declared static. Table 6-2. Class Member Types That Can Be Declared Static

Of course, you don t have to subscribe to events in methods called Subscribe you can do it anywhere you like!

When you re done watching an event for any reason, you can unsubscribe using the -= operator and another delegate to the same method. You can see that in the ProductionDeptTool1.Unsubscribe method. When you subscribe to an event your subscriber implicitly holds a reference to the publisher. This means that the garbage collector won t be able to collect the publisher if there is still a rooted reference to the subscriber. It is a good idea to provide a means of unsubscribing from events you are no longer actively observing, to avoid growing your working set unnecessarily. Let s add some code to our Main method to make use of the two new tools, as shown in Example 5-23.

static void Main(string[] args) { // ... ProductionDeptTool1 tool1 = new ProductionDeptTool1(); tool1.Subscribe(processor); ProductionDeptTool2 tool2 = new ProductionDeptTool2(); tool2.Subscribe(processor); documentBeingProcessed = "(Document 1)"; // ... } Console.ReadKey();

The previous examples demonstrate that object and array literals can contain other literals. Here is a more complex example:

If we compile and run, we now see the following output:

Data Members (Store Data)

Tool1 has seen Tool2 has seen The processing (Document 1) Too11 has seen Tool2 has seen processing. processing. will not succeed. that processing is complete. that processing is complete.

Document traduit. (Document 2) Spellchecked document. (Document 2) Repaginated document. (Document 2) Highlighting 'millennium' (Document 2) Too11 has seen that processing is complete. Tool2 has seen that processing is complete. Tool1 has seen processing. Tool2 has seen processing. Document traduit. (Document 3) Spellchecked document. (Document 3) Repaginated document. (Document 3) (Document 3) Too11 has seen that processing is complete. Tool2 has seen that processing is complete. Executed 9 processes.

You might notice that the event handlers have been executed in the order in which we added them. This is not guaranteed to be the case, and you cannot depend on this behavior. If you need deterministic ordering (as we did for our processes, for example) you should not use an event.

Earlier, I alluded to the fact that we can customize the data we send through with the event. We do this by deriving our own class from EventArgs, and adding extra properties or methods to it. Let s say we want to send the current document through in the event; we can create a class like the one shown in Example 5-24.

Function Members (Execute Code)

class ProcessEventArgs : EventArgs { // Handy constructor public ProcessEventArgs(Document document) { Document = document; } // // // // // // The extra property We don't want subscribers to be able to update this property, so we make it private (Of course, this doesn't prevent them from changing the Document itself)

}

public Document Document { get; private set; }

var team = { name:'', members:[], count:function() { return members.length } }

We also need to create a suitable delegate for the event, one that takes a ProcessEven tArgs as its second parameter rather than the EventArgs base class. We could do this by hand, sticking to the convention of calling the first parameter sender and the data parameter e:

delegate void ProcessEventHandler(object sender, ProcessEventArgs e);

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