Passing a variable from one form to another

[THURELL]

I have been a Mainframe programmer for 23 years & this is my first attempt at a C# app. I have a multiple form app that I need to pass a variable created in the first form to all other forms. The variable is populated by what is entered in a textbox on the first form
(iRinc = txtRincode.Text) and I need to be able to access that variable on all other forms. Help???

 

[johnrbradley]

Easiest way I found was just creating a new object origForm p, then access members of it using p.textBox1.Text, p.variable.toString() and any other variation.

 //in origForm

loadForm newForm = new loadForm(this);
newForm.ShowDialog(this);

//In newForm

private origForm origFormInstance;
public newForm(origForm p)
{
    origFormInstance = p;
    InitializeComponent();
    //Overload here and create
}

public newForm()
{
        InitializeComponent();
}

 

[THURELL]

John,
I greatly appreciate your response, however, I am really a beginner and in your example code you said 'overload here' and I am sorry to say I have no idea what you mean. Sorry!!

 

[johnrbradley]

By that I mean

public newForm(origForm p)
{//            ^^^^^^^^^^-overloading
    origFormInstance = p;
    InitializeComponent();
    
}

public newForm()
{
        InitializeComponent();
}

You have 2, one of which has 1 argument. The "public newForm(origForm p)" accepts this passed argument "this" in this case.
You would use this in origForm by:

private void showForm(object sender, System.EventArgs e)
{
     newForm newForm_show = newForm(this);
     newForm_show.ShowDialog(this);//or .Show()
     /*
       This shows the newForm 
       with the arugment "this", 
       which is origForm, in this example.
     */
}

 

[johnrbradley]

Change this:

newForm newForm_show = newForm(this);

To:

newForm newForm_show = new newForm(this);

 

[THURELL]

John,
Can you show me some sample code that works that does what I am trying to do? I tried with the info you gave me yesterday, but I can't get it to work.

 

[johnrbradley]

Alrighty, heres a quick example, mind you its long since it includes all of microsofts fluff.

Form1.cs

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace FormPassingDemo
{
	public class Form1 : System.Windows.Forms.Form
	{
		public System.Windows.Forms.TextBox textBox1;
		private System.ComponentModel.Container components = null;
		public Form1()
		{
			InitializeComponent();
		}
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		private void InitializeComponent()
		{
			this.textBox1 = new System.Windows.Forms.TextBox();
			this.SuspendLayout();
			this.textBox1.Location = new System.Drawing.Point(96, 120);
			this.textBox1.Name = "textBox1";
			this.textBox1.TabIndex = 0;
			this.textBox1.Text = "Hello";
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(292, 266);
			this.Controls.Add(this.textBox1);
			this.Name = "Form1";
			this.Text = "Form1";
			this.Load += new System.EventHandler(this.Form1_Load);
			this.ResumeLayout(false);

		}
		#endregion

		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
		}

		private void Form1_Load(object sender, System.EventArgs e)
		{
			Form2 f_new = new Form2(this);
			f_new.Show();
		}
	}
}

Form2.cs

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;

namespace FormPassingDemo
{
	public class Form2 : System.Windows.Forms.Form
	{
		private System.Windows.Forms.TextBox textBox1;
		private System.ComponentModel.Container components = null;
		private System.Windows.Forms.Button button1;
		private Form1 Form1_passed;
		public Form2()
		{
			InitializeComponent();
		}
		public Form2(Form1 p)
		{
			Form1_passed = p;
			InitializeComponent();
		}

		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if(components != null)
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		private void InitializeComponent()
		{
			this.textBox1 = new System.Windows.Forms.TextBox();
			this.button1 = new System.Windows.Forms.Button();
			this.SuspendLayout();
			this.textBox1.Location = new System.Drawing.Point(88, 112);
			this.textBox1.Name = "textBox1";
			this.textBox1.TabIndex = 0;
			this.textBox1.Text = "";
			this.button1.Location = new System.Drawing.Point(104, 144);
			this.button1.Name = "button1";
			this.button1.TabIndex = 1;
			this.button1.Text = "Get Form1";
			this.button1.Click += new System.EventHandler(this.button1_Click);
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(292, 266);
			this.Controls.Add(this.button1);
			this.Controls.Add(this.textBox1);
			this.Name = "Form2";
			this.Text = "Form2";
			this.Load += new System.EventHandler(this.Form2_Load);
			this.ResumeLayout(false);

		}
		#endregion

		private void Form2_Load(object sender, System.EventArgs e)
		{
		
		}

		private void button1_Click(object sender, System.EventArgs e)
		{
			textBox1.Text = Form1_passed.textBox1.Text;
		}
	}
}

 

[THURELL]

John,
I guess I will never make it as a C# programmer. I think I have my code just like the example you gave me and I get the following error:

test.Form1.textbox1 is inaccessible due to its protection level on the following line:
textBox1.Text = Form1_passed.textBox1.Text;

 

[THURELL]

John,
I got past the previous error I sent you about & now when I try to run it, I enter text in form1 and press enter and form2 displays with "textBox1" highlighted in form2 textbox not what I entered "1234". When I click on the button I get the following error:

An unhandled exception of type 'System.NullReferenceException' occurred in test.exe

Additional information: Object reference not set to an instance of an object.

 

[johnrbradley]

Are you sure you defined textBox1 as public in form1?
You were never supposed to press enter on the form1 text box. As it is designed now you should enter a value in form1, go to form2 and press "Get Form1" button, which should retrieve the value from Form1.textBox1.
Just in case reverify that you have:

public System.Windows.Forms.TextBox textBox1;

correctly written in your program.

Regards,
John

 

[THURELL]

John,
Yes, that was the first thing I had wrong. I changed that.
Unless I have something wrong both forms display at the same time, and when I enter somthing in Form1 and go to Form2 & click, it works. However, what I want to do is have the user enter data on form1, press enter, and then on form2 display some more data based on what they entered in form1. Can I get it to work that way??

 

[THURELL]

John,
After almost a week, I finally got it to work. You started me on the right track and I greatly appreciate your help. Now my next task will be to populate a list box from a database. I don't even want to think about it.
Thanks again!

 

[johnrbradley]

Glad to hear it , sorry for my rather slow replies, and populating a listbox from a database shouldn't be "too" hard , enjoy yourself.

Regards,
John