C# - 委托与事件
委托与事件委托
查看代码class Program
{
static void Main(string[] args)
{
Publisher publisher = new Publisher("篮球先锋报");
Observer observerA = new Observer("老A");
publisher.Magazine += observerA.RecvMagazine;
Observer observerB = new Observer("老B");
publisher.Magazine += observerB.RecvMagazine;
publisher.PublishMagezine();
//或者使用下面的方式区别就是一个在定义的内部触发，一个在外部触发
publisher.Magazine?.Invoke(publisher.magazineName);
Console.ReadKey();
}
}
public class Observer
{
private string name;
public Observer(string name)
{
this.name = name;
}
public void RecvMagazine(string message)
{
Console.WriteLine($"{this.name} recv {message}, 仔细读了一番");
}
}
public class Publisher
{
public string magazineName;
public Publisher(string magazineName)
{
this.magazineName = magazineName;
}
public delegate void MagazineDelegate(string message);
public MagazineDelegate Magazine;
public void PublishMagezine()
{
Magazine?.Invoke(this.magazineName);
}
}事件
查看代码class Program
{
static void Main(string[] args)
{
Publisher publisher = new Publisher("篮球先锋报");
Observer observerA = new Observer("老A");
publisher.Magazine += observerA.RecvMagazine;
Observer observerB = new Observer("老B");
publisher.Magazine += observerB.RecvMagazine;
publisher.PublishMagezine();
//下面的方式会出现编译错误只允许在定义的内部触发，不允许在外部触发
publisher.Magazine?.Invoke(publisher.magazineName);
Console.ReadKey();
}
}
public class Observer
{
private string name;
public Observer(string name)
{
this.name = name;
}
public void RecvMagazine(string message)
{
Console.WriteLine($"{this.name} recv {message}, 仔细读了一番");
}
}
public class Publisher
{
public string magazineName;
public Publisher(string magazineName)
{
this.magazineName = magazineName;
}
public delegate void MagazineDelegate(string message);
public event MagazineDelegate Magazine;
public void PublishMagezine()
{
Magazine?.Invoke(this.magazineName);
}
}经典面试题
猫叫、老鼠跑了，主人醒来了
查看代码class Program
{
static void Main(string[] args)
{
Cat cat = new Cat();
Mouse m = new Mouse(cat);
People p = new People(cat);
cat.Scream();
}
}
public class Cat
{
public delegate void ScreamHandler();
public event ScreamHandler OnScream;
public void Scream()
{
Console.WriteLine("猫叫了一声");
OnScream?.Invoke();
}
}
public class Mouse
{
public Mouse(Cat c)
{
c.OnScream += () => { Console.WriteLine("老鼠跑了"); };
}
}
public class People
{
public People(Cat c)
{
c.OnScream += () => { Console.WriteLine("主人醒来了"); };
}
}
//输出：
//猫叫了一声
//老鼠跑了
//主人醒来了委托与事件的区别
[*]事件基于委托，但并非委托 可以把事件看成委托的代理。在使用者看来，只有事件，而没有委托。
[*]事件是对委托的包装 保护委托字段，对外不开放。所以外部对象没法直接操作委托。提供了Add和Remove方法，供外部对象订阅事件和取消事件。事件的处理方法在对象外部定义，而事件的执行是在对象的内部。至于事件的触发，何时何地无所谓。
什么时候使用委托与事件？
如果一个委托不需要再其定义的类之外被触发，那么就可以将其转化为事件，这样可以保证它不会在外部被随意触发。
来源:https://www.cnblogs.com/ShenhaoCore/p/18181643
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