Passing Variables From File-to-File in C# - file

Question

How would I use a variable declared in Program.cs and access it's value from Form1.cs?
I know how to do this in C, but I'm completely lost in Microsoft's little twist on C.
Program.cs:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using LuaInterface;
namespace WindowsFormsApplication1
{
static class Program
{
public static Lua lua = null;
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
lua = new Lua();
}
}
}
Form1.cs
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;
using LuaInterface;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
lua.DoString("print('hi')");
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
}
private void textBox2_TextChanged(object sender, EventArgs e)
{
}
private void button2_Click(object sender, EventArgs e)
{
textBox1.Text = "";
}
}
}

Answer 1

Using your examples of Program.cs and Form1.cs and assuming these are the default names and that you have a Program class that instantiates a Form1 class and that you want to pass a parameter to the Form1 class, you can do the following:
Define a constructor for Form1 that takes this parameter and chain to the default constructor:
private Lua lua;
public Form1(Lua lua) : this()
{
this.lua = lua;
}
In your Program class when instantiating Form1, pass the parameter to it:
lua = new Lua();
Application.Run(new Form1(lua));
Note that I am using OOP terminology - objects and classes (not files).
Update:
Since you have declared your lua variable as a public static member of the Program class, you can access it anywhere in your program (assuming the namespaces have been declared appropriately) as follows:
Program.lua;
Though you would want to instantiate the static field before calling Application.Run.
In any way, this makes the object a public shared resource across all threads - making it virtually untestable and difficult to work with if you go multi-threaded.

Answer 2

You can also access the parameter with
Program.lua;
But Oded's way is cleaner.
And in Main, the object must be instantiated before Application.Run:
static void Main()
{
lua = new Lua();
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}

Answer 3

In Program.cs there is most probably a static class defined like this:
static class Program
{
...
}
If you declare the variable as public or internal, you will be able to access it from your form.
static class Program
{
public static int myVariable;
public static int MyProperty { get; set; }
}
In your form, you access the variable and the property with:
int i = Program.myVariable;
int j = Program.MyProperty;
In object-oriented programming, you would usually keep the variables private and only declare the properties as public.