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I am trying to use a customized List were I have added a few additional tools. I want to apply this list to a long list of customized classes that I have created. All of the classes have an ID number and some of the tools in the List use the ID.
Here is a portion of my code that I am trying to use. I hope this help you understand my problem.
namespace Simple_Point_of _Sales_System
{
public class MyList<T> : List<T>
{
internal int SetID()
{
return this.Max(n => n.ID) + 1;
}
internal T Find(int ID)
{
return this.Find(n => n.ID == ID);
}
internal T Add(T n)
{
Read();
Add(n);
Write();
return n;
}
internal void Remove(int ID)
{
Read();
if (this.Exists(t => t.ID == ID)) RemoveAll(t => t.ID == ID);
else MessageBox.Show(GetType().Name + " " + ID + " does not exist.", "Missing Item", MessageBoxButtons.OK, MessageBoxIcon.Error);
Write();
}
internal void Edit(int ID, T n)
{
Read();
if (this.Exists(t => t.ID == ID)) this[FindIndex(t => t.ID == ID)] = n;
else MessageBox.Show(GetType().Name + " " + ID + " does not exist.", "Missing Item", MessageBoxButtons.OK, MessageBoxIcon.Error);
Write();
}
internal MyList<T> Read()
{
Clear();
StreamReader sr = new StreamReader(@"../../Files/" + GetType().Name + ".txt");
while (!sr.EndOfStream)
Add(new T().Set(sr.ReadLine()));
sr.Close();
return this;
}
internal void Write()
{
StreamWriter sw = new StreamWriter(@"../../Files/" + GetType().Name + ".txt");
foreach (T n in this)
sw.WriteLine(n.ToString());
sw.Close();
}
}
public class Customer
{
public int ID;
public string FirstName;
public string LastName;
}
public class Item
{
public int ID { get; set; }
public string Category { get; set; }
public string Name { get; set; }
public double Price { get; set; }
}
public class MyClass
{
MyList<Customer> Customers = new MyList<Customer>();
MyList<Item> Items = new MyList<Item>();
}
}
610
List<T> class is the generic equivalent of ArrayList class by implementing the IList<T> generic interface. This class can use both equality and ordering comparer. List<T> class is not sorted by default and elements are accessed by zero-based index.
The following example shows how to create list and add elements. In the above example, List<int> primeNumbers = new List<int>(); creates a list of int type. In the same way, cities and bigCities are string type list. You can then add elements in a list using the Add() method or the collection-initializer syntax.
Lists in C# are very similar to lists in Java. A list is an object which holds variables in a specific order. The type of variable that the list can store is defined using the generic syntax. Here is an example of defining a list called numbers which holds integers.
The code is: struct m1 { public int a; public int b; } int main() { List <m1> mList; m1. initialize; //new.
I think your custom list needs to put on some constraints on the generic type to allow that. I would update your signature to something like
public class MyList<T> : List<T> where T : IIdentity { .... }
Here I used IIdentity as the interface defining ID, but it could also be a class.
To update your code I would do something like this:
public interface IIdentity
{
int ID { get; }
}
public class Customer : IIdentity
{
public int ID { get; set;}
public string FirstName;
public string LastName;
}
public class Item : IIdentity
{
public int ID { get; set; }
public string Category { get; set; }
public string Name { get; set; }
public double Price { get; set; }
}
I changed the ID in Customer to be a property instead of instance variable.
80
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