替代清单 <T> .ToString（）

Question

ok, im in learning stage already, make search and dont find, i want return .ToString() from my list<> but this in using

using System.Collections.Generic; 
using System.Text;

namespace eciv {
    using Pontos = List<Ponto>;  // I need override ToString()

    public partial class FPrincipal : Form  {

        private void button1_Click(object sender, EventArgs e)  {
            Pontos aa = new Pontos();
            aa.Add(new Ponto(2, 3));
            aa.Add(new Ponto(3, 4));
            textBox1.Text = aa.ToString();  // here I need help  
        }
    }

    public class Ponto {

        public double X;
        public double Y;

        public Ponto() {}

        public Ponto(double x, double y) { 
            this.X = x; this.Y = y; 
        }

        public Ponto(Ponto p) { 
            this.X = p.X; 
            this.Y = p.Y; 
        }

        public override string ToString() {
            string s = "(" + this.X.ToString() + "," + this.Y.ToString() + ")";
            return s;
        }
    }   
}

In textBox I get this value

System.Collections.Generic.List`1[eciv.Ponto]

I want something like this

((2,3),(3,4))

I think it's this but it doesn't work

public override string ToString() : Pontos {  
    StringBuilder s = new StringBuilder();
    s.Append("(");

    foreach (Ponto p in this) 
    {  
        s.Append(p.ToString() + ",");
    }

    s.Replace(",", ")", s.Length - 1, 1);
    return s.ToString();
}

Answer 1

You cannot override a method in some class if you are not inheriting from that class. So the solution is simple - instead of creating name alias, create a class which inherits List<Ponto> :

public class Pontos : List<Ponto>
{
    public override string ToString() => $"({String.Join(",", this)})";
}

Or format list in place:

textBox1.Text = $"({String.Join(",", aa)})"; // consider use meaningful names for variables

I would go for the second option if you want to convert pontos list to string only once - string formatting is not a good reason to introduce a new type.

---

If you need to convert this list to string several times, you can create some private or extension method for formatting list of objects (not necessary Ponto objects). Eg

public static string Stringify<T>(this IEnumerable<T> values)
   => $"({String.Join(",", values})";

And usage

textBox1.Text = aa.Stringify(); // works with List<int> etc

Links:

• String.Join - don't use StringBuilder if you want to join items in one string
• Extension Methods - extend existing classes with new functionality
• String Interpolation - nice new syntax for formatting strings

Answer 2

You can create your own List<T> , which overrides the ToString() -method

public class MyList<T> : List<T>
{
    public override string ToString()
    {
        StringBuilder s = new StringBuilder();
        s.Append("(");
        foreach (var element in this)
        {
            s.Append(element.ToString() + ",");
        }
        s.Replace(",", ")", s.Length - 1, 1);
        return s.ToString();
    }
}

Answer 3

Instead of calling ToString() on List<T> , you can create a string based on ToString() implementation you create for Ponto class like this:

Pontos aa = new Pontos();
aa.Add(new Ponto(2, 3));
aa.Add(new Ponto(3, 4));

StringBuilder s = new StringBuilder();
s.Append("(");
s.Append(String.Join(",", aa));
s.Append(")");

textBox1.Text = s.ToString();