C#构造函数事件
我创建了一个类,当我通过表单创建employee对象时,我想给出一条消息 这是我的班级、活动和代表C#构造函数事件,c#,events,C#,Events,我创建了一个类,当我通过表单创建employee对象时,我想给出一条消息 这是我的班级、活动和代表 public delegate void ctorDel(); class Employee { private int empID; private string empName; public event ctorDel myEvent; public Employee(int empID,string empName) { th
public delegate void ctorDel();
class Employee
{
private int empID;
private string empName;
public event ctorDel myEvent;
public Employee(int empID,string empName)
{
this.empID = empID;
this.empName = empName;
**if (myEvent != null)
{
myEvent();
}**
}
形式上
int id = Convert.ToInt16(textBox1.Text);
string name = textBox2.Text;
Employee emp = new Employee(id, name);
emp.myEvent += new ctorDel(showMessage);
和功能
public void showMessage()
{
MessageBox.Show("An employee is created");
}
您将在构造函数已经运行之后附加事件。在构造函数中引发实例事件没有意义,因为实例的初始化尚未完成,因此无法将任何处理程序附加到事件 但是,您可以创建一个静态事件:
public static event ctorDel myEvent;
...
Employee.myEvent += new ctorDel(showMessage);
(但不要每次创建
员工时都订阅该事件,否则处理程序将被调用的次数与实例的次数相同…创建员工时可以传递处理程序:
private Employee(ctorDel construcEvent)
{
if (construcEvent != null)
this.myEvent += construcEvent;
}
public Employee(int empID,string empName, ctorDel construcEvent)
: this(construcEvent)
{
this.empID = empID;
this.empName = empName;
if (myEvent != null)
{
myEvent();
}
}
然后:
Employee emp = new Employee(id, name, new ctorDel(showMessage));
你想达到什么目的?您尝试的方法不起作用的原因是,您正在将代理附加到ctor之后。一旦你给“新员工”打了电话,这个事件早就被解雇了
如果确实需要此类事件,请创建factory类:
public delegate void EmpCreated();
public EmployeeFactory {
public event EmpCreated myEvent;
public Employee Create(int empId, string empName){
var result = new Employee(empId, empName);
if(myEvent != null) myEvent();
return result;
}
}
订阅factory类上的事件,您将获得该事件。订阅此事件时,实例已经构建。
我建议使用工厂模式来隐藏构造函数
class EmployeeFactory
{
public Employee Create(int id, string name)
{
Employee instance = new Employee(id, name);
var handler = EmployeeCreated;
if (handler != null)
{
EmployeeEventArgs e = new EmployeeEventArgs(instance);
handler(e);
}
return instance;
}
public event EventHandler<EmployeeEventArgs> EmployeeCreated;
}
实例构建:
var emp = factory.Create(id, name);
解决方案
这里有一个解决问题的通用方法
public class EventFactory
{
public U Create<U, V>(V constructorArgs)
{
var instance = (U)Activator.CreateInstance(typeof(U), constructorArgs);
OnCreated?.Invoke();
return instance;
}
public delegate void CreatedEventHandler();
public event CreatedEventHandler OnCreated;
}
公共类事件工厂
{
公共U创建(V构造函数args)
{
var instance=(U)Activator.CreateInstance(typeof(U),constructorArgs);
OnCreated?.Invoke();
返回实例;
}
公共委托void CreatedEventHandler();
公共事件CreatedEventHandler OnCreated;
}
然后你就可以做了
var ef = new EventFactory();
ef.OnCreated += myEventHandler;
var instance = ef.Create<Employee>(employeeArgs);
var ef=new EventFactory();
ef.OnCreated+=myEventHandler;
var instance=ef.Create(employeeArgs);
.. 进一步
当需要传递事件参数或构造函数无参数时,可以调整我的代码以提供更大的灵活性。我还没有测试过它,但它应该看起来像
public class EventFactory<T>
{
public U Create<U, V>(V constructorArgs, T eventArgs)
{
var instance = (U)Activator.CreateInstance(typeof(U), constructorArgs);
OnCreated?.Invoke(eventArgs);
return instance;
}
public U Create<U>(T eventArgs)
{
return Create<U, object>(null, eventArgs);
}
public delegate void CreatedEventHandler(T args);
public event CreatedEventHandler OnCreated;
}
public class EventFactory
{
public U Create<U, V>(V constructorArgs)
{
var instance = (U)Activator.CreateInstance(typeof(U), constructorArgs);
OnCreated?.Invoke();
return instance;
}
public U Create<U>() where U : new()
{
var instance = new U();
OnCreated?.Invoke();
return instance;
}
public delegate void CreatedEventHandler();
public event CreatedEventHandler OnCreated;
}
公共类事件工厂
{
公共U创建(V构造函数args、T事件args)
{
var instance=(U)Activator.CreateInstance(typeof(U),constructorArgs);
OnCreated?.Invoke(eventArgs);
返回实例;
}
公共U创建(T事件参数)
{
返回Create(null,eventArgs);
}
公共委托无效CreatedEventHandler(T参数);
公共事件CreatedEventHandler OnCreated;
}
公共类事件工厂
{
公共U创建(V构造函数args)
{
var instance=(U)Activator.CreateInstance(typeof(U),constructorArgs);
OnCreated?.Invoke();
返回实例;
}
公共U Create(),其中U:new()
{
var实例=新的U();
OnCreated?.Invoke();
返回实例;
}
公共委托void CreatedEventHandler();
公共事件CreatedEventHandler OnCreated;
}
那么你的问题是什么?您在哪里遇到问题?myEvent将永远不会被解雇,因为它未设置在任何位置。没有人可以附加到事件,因此这毫无意义。我可以在employee构造函数中执行此操作吗?
public class EventFactory<T>
{
public U Create<U, V>(V constructorArgs, T eventArgs)
{
var instance = (U)Activator.CreateInstance(typeof(U), constructorArgs);
OnCreated?.Invoke(eventArgs);
return instance;
}
public U Create<U>(T eventArgs)
{
return Create<U, object>(null, eventArgs);
}
public delegate void CreatedEventHandler(T args);
public event CreatedEventHandler OnCreated;
}
public class EventFactory
{
public U Create<U, V>(V constructorArgs)
{
var instance = (U)Activator.CreateInstance(typeof(U), constructorArgs);
OnCreated?.Invoke();
return instance;
}
public U Create<U>() where U : new()
{
var instance = new U();
OnCreated?.Invoke();
return instance;
}
public delegate void CreatedEventHandler();
public event CreatedEventHandler OnCreated;
}