why is my class array element behaving like a pointer? (C#)

Question

I have this short windows form application code that i cannot get to work properly. It uses an instance of a class (as a temporary storage place) to populate an array of the same class type. It has a button and a textbox. If you press the button, the text is saved in the Name member and added to the array. If the Name is taken by another array member, it should show a message "name taken!" and not add it to the array. The problem is that this condition check is always true! if we type in "Marry", the debugger shows that

 if (examleArray[i].Name == temp.Name)

is equivalent to:

if ("Marry" == "Marry")

as if one is pointing to the other. Why is this? how do i fix it? thank you!

namespace errorexample
{
    public partial class Form1 : Form
    {

        example temp = new example();
        example[] examleArray = new example[10];
        int examleArrayIndex = 0;
        bool NameTaken = false;

        public Form1()
        {  InitializeComponent();  }

        private void button1_Click(object sender, EventArgs e)
        {
            temp.Name = textBox1.Text;         
            NameTaken = false;

            for (var i = 0; i < (examleArrayIndex); i++)
            {
                if (examleArray[i].Name == temp.Name)
                {
                    NameTaken = true;
                    MessageBox.Show("Name taken!");
                }

            }

            if (NameTaken == false)
            {
                examleArray[examleArrayIndex] = temp;
                examleArrayIndex++;
            }
        }
    }

    public class example {
        public string Name;  
    }

}

Because there is only one instance of example in your form, you keep reusing it — user555045
– user555045, Commented Dec 2, 2016 at 17:42
Because you have an array of references that all point to the same example object since you only create one. — juharr
– juharr, Commented Dec 2, 2016 at 17:44

Robert McKee · Accepted Answer · 2016-12-02 17:49:35Z

1

You only have one temp object, and you add keep adding it to the array. It's the same temp since you never create a new one. I've rewritten it for you:

 List<example> examleArray = new List<example>();
 private void button1_Click(object sender, EventArgs e)
 {
   if (examleArray.Any(e=>e.Name == textBox1.Text))
   {
     MessageBox.Show("Name taken!");
   } else {
     examleArray.Add(new example { Name = textBox1.Text });
   }
 }

I've also converted your fixed array into a List so you don't ever accidentally try and add 11 names and then blow up. And I've converted your search to LINQ to simplify.

answered Dec 2, 2016 at 17:49

Robert McKee

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Comments

clcto · Accepted Answer · 2016-12-02 17:46:32Z

0

You only create one example object. You are putting multiple references to the same object into the array. One solution is to create a new example object to put in the array:

public class example {
    public string Name;
    public example( string name ){
        Name = name;
    }
}

//...
examleArray[examleArrayIndex] = new example( temp.Name );

answered Dec 2, 2016 at 17:46

clcto

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Comments

Damith · Accepted Answer · 2016-12-02 17:51:37Z

move temp object initialization inside the click event, otherwise you are updating same object

private void button1_Click(object sender, EventArgs e)
        {
            example temp = new example();
            temp.Name = textBox1.Text;         
            NameTaken = false;

            for (var i = 0; i < (examleArrayIndex); i++)
            {
                if (examleArray[i].Name == temp.Name)
                {
                    NameTaken = true;
                    MessageBox.Show("Name taken!");
                }

            }

            if (NameTaken == false)
            {
                examleArray[examleArrayIndex] = temp;
                examleArrayIndex++;
            }
        }

you can use List

List<string> example =
        new List<string>();

if(example.Contains(textBox1.Text))
{ 
  MessageBox.Show("Name taken!");
}else
{
  example.Add(textBox1.Text);
}

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