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How to access class array from another form

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How to access class array from another form
Junije
post 8 Jul, 2008 - 09:39 AM
Post #1


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Hi, I'm just switching from VB 6.0 to C# and have some problems with the transition.

My project has 2 forms, (Form1, and Form2), and 1 Class file(Person.cs).

In my main form, Form1, I've declared

CODE


public partial  class Form1 : Form
    {

// This is my user array ( from the class Person.cs)
Person[] User = new Person[10];

...

     public void Form1_Load(object sender, EventArgs e)
        {

            User[0] = new Person();
            User[0].Name = "Mike";
            User[0].Age = 21;
            User[0]....



From the same form I can easily access all the user arrays and change the properties.
But when I try to access them from the other form, for some reason It doesn't work sad.gif

In Form2, I want to change certain User[0] properties when clicking on a button, but the Code view in Form2 doesn't recognize the User[] array.

This is probably a very simple problem, but I'm a newbie and I don't know much, so I hope someone can help me =).
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baavgai
post 8 Jul, 2008 - 10:09 AM
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QUOTE(Junije @ 8 Jul, 2008 - 12:39 PM) *

This is probably a very simple problem, but I'm a newbie and I don't know much, so I hope someone can help me =).


That depends, actually.

First, try making the array public, like this:
csharp

public Person[] User = new Person[10];


Now, if your form2 is doing something like this, you're fine.
csharp

Form1 form1Instance = new Form1();
form1Instance.ShowDialog();
Person[] User = form1Instance.User;


However, if you want to access the thing globally and have an instance, you have a host of issues.

I'm going to guess that Form2 might be a dialog for modify a Person object? If so, consider something like this.

csharp

public partial class Form2 : Form {
	// my reference to a person object
	private Person person;
	
	// how other objects access my person object
	public Person CurrentPerson {
		get { return this.person; }
		set { this.person = value; }
	}
}

public partial  class Form1 : Form {
	private void EditPerson(Person person) {
		Form2 frm = new Form2();
		frm.CurrentPerson = person;
		frm.ShowDialog();
	}
	
	public void Button3_Click(object sender, EventArgs e) {
		EditPerson(this.User[2]);
	}
}


If this is confusing, please read up on classes and object / instances. Completely understand what static means and the difference between an object and a class method. Trading values around between objects is a very common confusion. Unfortunately, there are a number of ways to approach the problem, so there's no single correct answer.

Hope this helps.
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zakary
post 8 Jul, 2008 - 10:11 AM
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can you post the code for form2
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Junije
post 8 Jul, 2008 - 10:42 AM
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Hey, thanks for the answer bavgaii.

I've tried making the array public but it still doesn't get recognized in the Form2 when i type User[0].

I'll try the other things you wrote...

As for code in the Form2, it's really not much important I guess, but I have a button, and a listbox.
What I'm trying to do is when I open the Form2 (from the Form1 interface), and then click on the button, the listbox would then show all the User[] information( Name, Age...).
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Junije
post 8 Jul, 2008 - 01:30 PM
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I've tried this and it seems you're on the right way.

CODE

   1. Form1 form1Instance = new Form1();  
   2. form1Instance.ShowDialog();  
   3. Person[] User = form1Instance.User;  


The User[] Array gets recognized while typing but when building the application I get an error sad.gif

The error stands:
CODE


Error    1    The type 'WindowsFormsApplication1.Form1' already contains a definition for 'User'




And it highlights this part of the code in the Form1(which i didn't write, I guess it appeared when I declared the array):

CODE


        internal Person[] User()
        {
            throw new NotImplementedException();
        }





This is my whole form2 code, maybe I just need to place the code differently or modify something to make the error disappear, I don't have much experience in C# so the tiny problems that appear out of nowhere really bug me sometimes smile.gif.

CODE


using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form2 : Form
    {

        

        public Form2()
        {
            InitializeComponent();
            
        }

          
      


        Form1 form1Instance = new Form1();
        Person[] User = form1Instance.User;


        private void Form2_Load(object sender, EventArgs e)
        {


            form1Instance.ShowDialog();
            

        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {

         // Just trying to change the property as a test if it works, but it doesn't :(
            
         User[0].Age = 34;

          
        }
    }
}
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eclipsed4utoo
post 8 Jul, 2008 - 01:39 PM
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add this to Form2 above the constructor...

csharp

public Person[] User;


then add this to Form1 where you want Form2 to open...

csharp

Form2 form2Instance = new Form2();
form2Instance.User = User;
form2Instance.ShowDialog();


then remove these lines from Form2....

csharp

        Form1 form1Instance = new Form1();
        Person[] User = form1Instance.User;


then remove this line from the Form2 Load Event...
csharp

form1Instance.ShowDialog();


This post has been edited by eclipsed4utoo: 8 Jul, 2008 - 01:44 PM
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Junije
post 8 Jul, 2008 - 02:18 PM
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Aarrghh.....I'm getting the same error as before :S

I'm new to these "classes", maybe I should have gone with the structs to build the array.

Thanks for the help everyone. biggrin.gif

I'll try and mess around with code, and read some stuff , maybe I'll solve it...
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eclipsed4utoo
post 8 Jul, 2008 - 06:06 PM
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can you post the code that you have now?
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Junije
post 9 Jul, 2008 - 04:53 AM
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I've done everything you wrote, but I'm getting an error:

CODE

Error    1    Form2.User' is inaccessible due to its protection level


Highlighting this part of the code:

CODE

form2Instance.User = User;


The full code of my project is shown here:

Form1:

CODE

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Project
{
    public partial class Form1 : Form
    {

        Person[] User = new Person[10];
         // If I make this above public, I get a different error:
         // Error    1    Inconsistent accessibility: field type  'Project.Person[]' is less accessible than field 'Project.Form1.User'    

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            

            User[0] = new Person();
            User[0].Name = "Mike";
            User[0].Age = 21;
            User[0].Gender = 0;

        }

        private void button1_Click(object sender, EventArgs e)
        {
                Form2 form2Instance = new Form2();  
                form2Instance.User = User;  
                form2Instance.ShowDialog();  
        }
    }
}



Form2:

CODE


using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Project
{
    public partial class Form2 : Form
    {

         Person[] User;  
         // If I make this above public, I get a different error:
         // Error    1    Inconsistent accessibility: field type  'Project.Person[]' is less accessible than field 'Project.Form2.User'    




        public Form2()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

            listBox1.Items.Add("User[0].Name = " + User[0].Name);

        }

        private void Form2_Load(object sender, EventArgs e)
        {

        }
    }
}




This problem is a real pain in the ass... biggrin.gif
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eclipsed4utoo
post 9 Jul, 2008 - 05:08 AM
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you need to make the Person[] array on Form2 public.
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Junije
post 9 Jul, 2008 - 05:53 AM
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Unfortunatly making the Person[] array public doesn't work, I get the error as stated in the code above ( commented section).

Is there any other way I can make the array available to the whole project, not just to the Form it was declared in?

I don't know why things have to be so complicated, and why the array isn't available to the other Forms in the first place.

Would the array from a parent form be accessible from a child form, i guess this could offer one solution to my problem?
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eclipsed4utoo
post 9 Jul, 2008 - 06:05 AM
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here is sample code on one way to pass variables between forms:

Form1...

csharp

    public partial class Form1 : Form
    {
        private string[] array = null;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            array[0] = "test";

            Form2 form2 = new Form2();
            form2.secondArray = array;
            form2.ShowDialog();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            array = new string[1];
        }
    }


Form2:

csharp

    public partial class Form2 : Form
    {
        public string[] secondArray = null;

        public Form2()
        {
            InitializeComponent();
        }

        private void Form2_Load(object sender, EventArgs e)
        {
            lblBefore.Text = secondArray[0].ToString();

            secondArray[0] = "test2";

            lblAfter.Text = secondArray[0].ToString();
        }
    }


"lblBefore" on Form2 shows "test", "lblAfter" on Form2 shows "test2".

QUOTE(Junije @ 9 Jul, 2008 - 05:53 AM) *

Unfortunatly making the Person[] array public doesn't work, I get the error as stated in the code above ( commented section).

Is there any other way I can make the array available to the whole project, not just to the Form it was declared in?

I don't know why things have to be so complicated, and why the array isn't available to the other Forms in the first place.

Would the array from a parent form be accessible from a child form, i guess this could offer one solution to my problem?


there are multiple ways of passing parameters. Using properties/public variables(like the example above) or passing the data through the constructor.
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