在下面的控制台应用程序示例中,事件 定义如下:
public delegate void PurchaseHandler(object obj, PurchaseArgs args);
public event PurchaseHandler OnPurchaseMade;
在阅读之后我觉得这可能有点“C#2”。
是否有更简洁的方式用 C#3 和 C#4 来表达它?
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);
}
}
}
最佳答案
总是这样定义事件,不要使用自定义委托(delegate):
event EventHandler<EventArgsClassType> MyEventHandler;
或者,如果他们不接受参数:
event EventHandler MyEventHandler;
基于 System.EventHandler
类,这确保了所有事件的统一签名,遵循 .NET 准则。
如果您的事件需要更多参数,则其 EventArgsClassType
必须继承自 System.EventArgs
。
此外,在实例化事件处理程序时,您不必使用这种显式形式:
product1.OnPurchaseMade += new Product.PurchaseHandler(NotifyUser);
因为方法组可以隐式转换为匹配的委托(delegate)。因此,以下代码同样有效:
product1.OnPurchaseMade += NotifyUser;
关于c# - 在 C#3 和 C#4 中是否有更简洁的方法来定义自定义事件?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2820054/