[英]Is there a more abbreviated way to define a custom event in C#3 and C#4?
在以下控制台應用程序示例中, 事件定義如下:
public delegate void PurchaseHandler(object obj, PurchaseArgs args);
public event PurchaseHandler OnPurchaseMade;
在看完之后我覺得這可能有點“ C#2 ”。
是否有更簡潔的方式來表達C#3和C#4?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace TestEvents288202
{
class Program
{
static void Main(string[] args)
{
Product product1 = Product.LoadProduct(222);
EmailManager.NotifyAdministrator(product1);
product1.OnPurchaseMade += new Product.PurchaseHandler(NotifyUser);
product1.Purchase();
Product product2 = Product.LoadProduct(333);
EmailManager.NotifyAdministrator(product2);
product2.OnPurchaseMade += new Product.PurchaseHandler(NotifyUser);
product2.Purchase();
Console.ReadLine();
}
static void NotifyUser(object sender, PurchaseArgs e)
{
((Product)sender).Log();
Console.WriteLine(e.Message);
}
}
public static class EmailManager
{
public static void NotifyAdministrator(Product product)
{
product.OnPurchaseMade += new Product.PurchaseHandler(SendEmail);
}
public static void SendEmail(object sender, PurchaseArgs e)
{
Product product = sender as Product;
Console.WriteLine("Just sent e-mail to administrator notifying of purchase of article {0}", product.ProductNumber);
}
}
public class PurchaseArgs : EventArgs
{
public string Message { get; set; }
public PurchaseArgs(string message)
{
Message = message;
}
}
public class Product
{
public int ProductNumber { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public delegate void PurchaseHandler(object obj, PurchaseArgs args);
public event PurchaseHandler OnPurchaseMade;
public static Product LoadProduct(int productNumber)
{
List<Product> products = new List<Product>();
products.Add(new Product { ProductNumber = 111, Name = "Intel CPU", Description = "Newest model, very fast." });
products.Add(new Product { ProductNumber = 222, Name = "Philips Monitor", Description = "22-inch, very nice." });
products.Add(new Product { ProductNumber = 333, Name = "Sony Camera", Description = "10 Megapixels, sharp pictures." });
return products.Where(p => p.ProductNumber == productNumber).SingleOrDefault();
}
public void Purchase()
{
PurchaseArgs purchaseArgs = new PurchaseArgs(String.Format("The product \"{0}\" was just purchased.", this.Name));
OnPurchaseMade(this, purchaseArgs);
}
public void Log()
{
Console.WriteLine("Log: #{0} purchased.", this.ProductNumber);
}
}
}
始終定義這樣的事件,不要使用自定義委托:
event EventHandler<EventArgsClassType> MyEventHandler;
或者,如果他們不參數:
event EventHandler MyEventHandler;
通過基於System.EventHandler
類,這可以確保遵循.NET准則的所有事件的統一簽名。
如果您的事件需要進一步的參數,則其EventArgsClassType
必須從System.EventArgs
繼承。
此外,在實例化事件處理程序時,您不必使用此顯式形式:
product1.OnPurchaseMade += new Product.PurchaseHandler(NotifyUser);
因為方法組可以隱式轉換為匹配的委托。 因此,以下代碼也可以正常工作:
product1.OnPurchaseMade += NotifyUser;
嘗試這個:
public event EventHandler<PurchaseArgs> OnPurchaseMade;
還有,像這樣的行:
product1.OnPurchaseMade += new Product.PurchaseHandler(NotifyUser);
可以簡化:
product1.OnPurchaseMade += NotifyUser;
首先,您可以使用EventHandler模板來創建委托,因此您的代碼將是:
public event EventHandler<PurchaseArgs> OnPurchaseMade;
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