C Sharp

Creating Delegates Only When Needed

In the two examples you've seen so far, the delegate is created whether or not it's ever used. That was fine in those examples because I knew that it would always be called. However, when defining your delegates, it's important to consider when to create them. Let's say, for example, that the creation of a particular delegate is time-consuming and not something you want to do gratuitously. In these situations in which you know the client won't typically call a given callback method, you can put off the creation of the delegate until it's actually needed by wrapping its instantiation in a property. To illustrate how to do this, a modification of the DBManager class follows that uses a read-only property-because only a getter method is present-to instantiate the delegate. The delegate will not be created until this property is referenced.

using System;
class DBConnection
{
    public DBConnection(string name)
    {
        this.name = name;
    }
    protected string Name;
    public string name
    {
        get
        {
            return this.Name;
        }
        set
        {
            this.Name = value;
        }
    }
}
class DBManager
{
    static DBConnection[] activeConnections;
    public void AddConnections()
    {
        activeConnections = new DBConnection[5];
        for (int i = 0; i < 5; i++)
        {
            activeConnections[i] = new
                DBConnection("DBConnection " + (i + 1));
        }
    }
    public delegate void EnumConnectionsCallback(DBConnection connection);
    public static void EnumConnections(EnumConnectionsCallback callback)
    {
        foreach (DBConnection connection in activeConnections)
        {
            callback(connection);
        }
    }
}
class Delegate3App
{
    public DBManager.EnumConnectionsCallback myCallback
    {
        get
        {
            return new DBManager.EnumConnectionsCallback
                            (ActiveConnectionsCallback);
        }
    }
    public static void ActiveConnectionsCallback(DBConnection connection)
    {
        Console.WriteLine
            ("Callback method called for " + connection.name);
    }
    public static void Main()
    {
        Delegate3App app = new Delegate3App();
        DBManager dbMgr = new DBManager();
        dbMgr.AddConnections();
        DBManager.EnumConnections(app.myCallback);
    }
}

by BrainBellupdated
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