C# ArrayList - object

Question

I have three classes in my C# program. Get the following error:

Cannot implicitly convert type 'object' to 'Register_Employee.Employee'. An explicit conversion exists (are you missing a cast?) C:\Users\x64\Documents\Visual Studio 2010\Projects\Register Employee\Register Employee\EmployeeList.cs 20 20 Register Employee

I know what the problem is. You have to return the correct type of object, but I don't know how to solve it. I have a class Employee, a class EmployeeList which holds employees and the main program.

namespace Register_Employee
{
    class EmployeeList
    {
        ArrayList list = new ArrayList();

       public void addEmployee(Employee a)
       {
           this.list.Add(a);
       }

        public Employee GetEmployee(int Index)
        {
            var e = list[Index]; <<<<<The problems
            return e;  <<<<<The problems
        }

    }
}

namespace Register_Employee
{
    class Employee
    {

        public Employee(String iD, String firstName, String lastName)
        {
            this.ID = iD;
            this.FirstName = firstName;
            this.LastName = lastName;
        }

        public String ID { get; set; }
        public String FirstName { get; set; }
        public String LastName { get; set; }


    }
}

Thanks in advance

Why are you using ArrayList when List<Employee> would be more descriptive and type safe? — Oded
– Oded, Commented Jan 20, 2012 at 12:33
Out of interest, why are you still using non-generic collections? — Jon Skeet
– Jon Skeet, Commented Jan 20, 2012 at 12:33
Hi! I very new to programming and I don't know what you mean by that, non-generic collections that is. — Mårten Cederholm
– Mårten Cederholm, Commented Jan 21, 2012 at 1:50

Strillo · Accepted Answer · 2012-01-20 12:31:51Z

4

As the error message says, you need to explicitly cast:

Employee e = (Employee)list[Index];

Also, you could use a List<Employee> instead of ArrayList.

answered Jan 20, 2012 at 12:31

Strillo

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Comments

rerun · Accepted Answer · 2012-01-20 12:37:11Z

3

You can solve the problem in a couple of ways.

First if a thing is stored as an object but is actually a derived type you can always cast it to the appropriate type.

public Employee GetEmployee(int Index)
    {
        var e = list[Index]; 
        return (Employee)e; 
    }

However you loose type safety in doing so. A better solution is to use generics

class EmployeeList
{
   List<Employee> list = new List<Employee>();

   public void addEmployee(Employee a)
   {
       this.list.Add(a);
   }

    public Employee GetEmployee(int Index)
    {
        var e = list[Index]; 
        return e;  //No cast needed 
    }

}

In this case you know have a list which supports type safety (ie you know everything in it is a Employee ) and will actually out perform the array list.

answered Jan 20, 2012 at 12:37

rerun

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1 Comment

phoog Over a year ago

+1 for discussing the benefits of the generic List rather than just suggesting its use.

Amar Palsapure · Accepted Answer · 2012-01-20 12:47:45Z

3

You will need to type cast object to Employee object

public Employee GetEmployee(int Index)
{
    var e = list[Index]; 
    return (Employee)e;  
}

.Net framework 2.0 or later has a generic class List which you can use instead of ArrayList. Represents a strongly typed list of objects that can be accessed by index. Check on MSDN.

In that case

class EmployeeList
{
    List<Employee> list = new List<Employee>();
    //Rest of your code
}

Hope this helps you.

edited Jan 20, 2012 at 12:47

answered Jan 20, 2012 at 12:33

Amar Palsapure

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1 Comment

Henk Holterman Over a year ago

"if your ... 2.0 or later" : notice the var.

Henk Holterman · Accepted Answer · 2012-01-20 12:32:05Z

2

Just use

public Employee GetEmployee(int Index)
{
  var e = list[Index];  // should work, e will be of type Object
  return (Employee) e; // <<<<<The problems
}

And consider using List<Employee> to have a more 'type-safe' collection.

class EmployeeList
{
    //ArrayList list = new ArrayList();
    List<Employee> list = new List<Employee>();
    ...
}

answered Jan 20, 2012 at 12:32

Henk Holterman

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Comments

Not-RocketScience · Accepted Answer · 2012-01-20 12:36:29Z

2

Cast the object to the Employee object. Use List if you have the option.

answered Jan 20, 2012 at 12:36

Not-RocketScience

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Comments

Guillaume Slashy · Accepted Answer · 2012-01-20 13:06:39Z

1

Just cast the object as an Employee Change this

var e = list[Index]; <<<<<The problems

To this

var e = (Employee)list[Index]; <<<<<The problems

like a couple of guys said, you should definitely NOT use a generic Collection/List/IEnumerable

answered Jan 20, 2012 at 13:06

Guillaume Slashy

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Comments

phoog · Accepted Answer · 2012-01-20 14:09:15Z

1

The other answers here suggest or imply that you should use

List<Employee>

rather than ArrayList in your EmployeeList class. From your sample, it seems that EmployeeList is just a strongly-typed wrapper around ArrayList. If that's the case, you can get rid of EmployeeList entirely and use

List<Employee>

instead.

answered Jan 20, 2012 at 14:09

phoog

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4 Comments

Mårten Cederholm Over a year ago

Got the same problem again, can't understand it know public int count() { int p = 0; int counter = 0; var e = new Employee(); while(p == 0) { e = list[counter]; } }

phoog Over a year ago

@MårtenCederholm what is the problem? The code fragment in your comment is an infinite loop that does essentially nothing. What is it supposed to do?

Mårten Cederholm Over a year ago

Sorry, List<Employee> EmployeeList = new List<Employee>();

phoog Over a year ago

@MårtenCederholm And what's the problem with that statement? Perhaps you should edit your question to post the current state of your code and describe the current problem. Or perhaps a new question is warranted.

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