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if (price == value) return;
OnPriceChanged (new PriceChangedEventArgs (price, value));
price = value;
}
}
}
class Test
{
static void Main()
{
Stock stock = new Stock ("THPW");
stock.Price = 27.10M;
// Register with the PriceChanged event
stock.PriceChanged += stock_PriceChanged;
stock.Price = 31.59M;
}
static void stock_PriceChanged (object sender, PriceChangedEventArgs e)
{
if ((e.NewPrice - e.LastPrice) / e.LastPrice > 0.1M)
Console.WriteLine ("Alert, 10% stock price increase!");
}
}
The predefined nongeneric EventHandler delegate can be used when an event doesn’t
carry extra information. In this example, we rewrite Stock such that the Price
Changed event is fired after the price changes, and no information about the event is
necessary, other than it happened. We also make use of the EventArgs.Empty property,
in order to avoid unnecessarily instantiating an instance of EventArgs.
public class Stock
{
string symbol;
decimal price;
public Stock (string symbol) { this.symbol = symbol; }
public event EventHandler PriceChanged;
protected virtual void OnPriceChanged (EventArgs e)
{
if (PriceChanged != null) PriceChanged (this, e);
}
public decimal Price
{
get { return price; }
set
{
if (price == value) return;
price = value;
OnPriceChanged (EventArgs.Empty);
}
}
}
128 | Chapter 4: Advanced C#