C# Func delegate in combination with lambda expression not correct
I have a class Employee, with some basic params, and a class employees that has a list of employee objects. I want to use the func delegate in the class employees to be able to use the following lambda expression in the main class. I think I have some syntax mistakes here... I'am getting the following error message: "cannot convert lambda expression to type 'Employee' because it is not a delegate type".
Someone knows what I'am doing wrong?
Many thanks guys !!
static void Main(string[] args)
{
Employees lijst = new Employees();
lijst.Add(new Employee("B1", 200));
lijst.Add(new Employee("B2", 100));
lijst.Add(new Employee("B3", 300));
lijst.Wijzig((Employee b) => b.Salary += 100);
Console.ReadKey();
}
class Employee
{
public String Name { get; set; }
public int Salary { get; set; }
public Employee(String Name, int Salary)
{
this.Name = Name;
this.Salary = Salary;
}
}
class Employees
{
public Func<Employee, int> Wijzig = new Func<Employee, int>(Change);
private ArrayList _lijst = new ArrayList();
public void Add(Employee e)
{
_lijst.Add(e);
}
static int Change(Employee b)
{
return 0;
}
}
这是我的解决方案，在Main函数中没有改变：
static void Main(string[] args)
{
Employees lijst = new Employees();
lijst.Add(new Employee("B1", 200));
lijst.Add(new Employee("B2", 100));
lijst.Add(new Employee("B3", 300));
lijst.Wijzig((Employee b) => b.Salary += 100);
lijst.Print();
Console.ReadKey();
}
class Employee
{
public String Name { get; set; }
public int Salary { get; set; }
public Employee(String Name, int Salary)
{
this.Name = Name;
this.Salary = Salary;
}
}
class Employees
{
// [Delete]
// public Func<Employee, int> Wijzig = new Func<Employee, int>(Change);
private ArrayList _lijst = new ArrayList();
public void Add(Employee e)
{
_lijst.Add(e);
}
// [Delete]
//static int Change(Employee b)
//{
// return 0;
//}
// [New]
public void Wijzig(Func<Employee, int> func)
{
foreach (Employee e in _lijst)
{
func(e);
}
}
public void Print()
{
foreach (Employee e in _lijst)
{
Console.WriteLine(e.Name + "t" + e.Salary);
}
}
}
Wijzig is a delegate of type Func<Employee, int> . Ie it's a method which accepts employee object and returns an integer. So lijst.Wijzig returns this delegate. If you want to invoke this delegate, you should pass employee object (according to signature Func<Employee, int> ), but you are passing lambda delegate instead of an employee. Correct invocation:
lijst.Wijzig(someEmployee); // calls Employees.Change
That will invoke a int Change(Employee b) method. But seems like you don't want to invokde Change method (which does nothing, except returning zero). You want to invoke some real change - increment of salary. So, the first step you should do is change the delegate wich is assigned to Wijzig , and then invoke this delegate with your employee object:
lijst.Wijzig = (Employee b) => { b.Salary += 100; return 0; }
lijst.Wijzig(someEmployee); // calls lambda which we assigned
Notes:
ArrayList in .NET 2.0+ you should use generic collection like List<Employee> instead. Change method returns an integer. Consider making it void. you are re-implementing functionality LINQ - there is a ForEach extension method which accepts an action to be performed on each item of the collection.
var list = new List<Employee> {
new Employee("B1", 200),
new Employee("B2", 100),
new Employee("B3", 300)
};
list.ForEach(e => e.Salary += 100);
That's it. All your code without custom classes.
Your below code line to invoke func
lijst.Wijzig((Employee b) => b.Salary += 100);
should just be below, passing an Employee object
int result = lijst.Wijzig(lijst[0]);