Question

My application currently has 2 forms. It creates a sub form, Form2, which ends with the following code:

public partial class Form2 : Form
{ ...
    Form1 frm = new Form1();
        frm.rglu = glu;
        frm.rdate = fulldate;
        frm.sort();
    Close();
}

Note that form1 is just a couple of buttons at the moment. One starts off Form2 as follows:

    private void button2_Click(object sender, EventArgs e)
    {
        using (Form2 AcqForm = new Form2())
        {
            AcqForm.ShowDialog(this);
        }
    }

No other code runs except a button test(); shown later).
This frm.sort(); runs the following code found in Form1:

public partial class Form1 : Form
{
    public void sort() 
    {           
        datelist = new List<DateTime>(rdate);
        datelist.Sort((a, b) => a.CompareTo(b));

        var result = rdate
        .Select((d, i) => new { Date = d, Int = rglu[i] }) 
        .OrderBy(o => o.Date) 
        .ToArray();

        this.rdate = result.Select(o => o.Date).ToArray();
        this.rglu = result.Select(o => o.Int).ToArray();  //all works fine

        for (int i = 7; i+7 <= rglu.Length; i++)
        {
    Console.WriteLine(Convert.ToString(rdate[i]) + Convert.ToString(rglu[i]));
        } //This shows values as expected
    }
}

However when I set a button to run some more code using rglu and rdate the I get null pointer errors:

public partial class Form1 : Form
{ 
    private void test(object sender, EventArgs e)
    {
        for (int i = 7; i < rglu.Length; i++){} //rglu is null! The values are lost.
    }
}

I believe the solution requires a int[] rglu {get; set;} method. However so far I have been unsuccessful in using these things at all. Has anyone encountered this problem?

Edit:
rglu is defined like this:

public int[] rglu { get; set; } //I don't get how this works though

Answer 1

Problem is in form2,
You mustn’t write ‘Form1 frm = new Form1();’ this code.

in Form1 wite code like this:

using System;
using System.Collections.Generic;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public int rglu;
        public DateTime rdate;

        public Form1()
        {
            InitializeComponent();
        }

        private void btnShowForm2_Click(object sender, EventArgs e)
        {
            Form2 frm2=new Form2();
            frm2.Form1Instance = this;
            frm2.Show();
        }
        public void sort()
        {
            datelist = new List<DateTime>(rdate);
            datelist.Sort((a, b) => a.CompareTo(b));

            var result = rdate
            .Select((d, i) => new { Date = d, Int = rglu[i] })
            .OrderBy(o => o.Date) // Sort by whatever field you want
            .ToArray();

            this.rdate = result.Select(o => o.Date).ToArray();
            this.rglu = result.Select(o => o.Int).ToArray();  //all works fine

            for (int i = 7; i + 7 <= rglu.Length; i++)
            {
                Console.WriteLine(Convert.ToString(rdate[i]) + Convert.ToString(rglu[i]));
            } //This returns values as expected
        }
    }
}

in Form2 write codes like this:

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form2 : Form
    {
        public Form1 Form1Instance;
        public Form2()
        {
            InitializeComponent();
        }

        private void btnSortValues_Click(object sender, EventArgs e)
        {
            Form1Instance.rglu = glu;
            Form1Instance.rdate = fulldate;
            Form1Instance.sort();
            Close();
        }
    }
}