How to access Form1 controls from another class?

ben sen

Hi all c#corner forums,
I'm trying to create my class, but I couldn't succeed to work this code. When I run program, newSerial.sendData() in the Form1.Load() (this is my function which is in my own class) works perfectly, but when I clicked the button (you can see the code, I'm calling the same function) program throws "NullReferenceException" error. What is the solution?

[CODE]
namespace robitSeri
{

public partial class Form1 : Form
{
public mySerial newSerial;

private void Form1_Load(object sender, EventArgs e) { mySerial newSerial = new mySerial(this); newSerial.sendData();

// THIS WORKS EXCELLENTLY..
}
private void button1_Click(object sender, EventArgs e)
{
newSerial.sendData();
// THIS CODE DOES NOT WORK!!!
}

// this is original class which is automatically created when
// I create new Windows Form application
// And I can control everything when I'm coding in this class
}

public class mySerial // this class created by me
{
private Form1 frm;

public mySerial(Form1 newFrm)
{
this.frm=newFrm;
}

public void sendData()
{
frm.serialPort1.Write(sth);
}

// I can't reach Form1 controls from this class.
}
[/CODE]

4 Replies

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ben sen15y ago
I'm trying to do that for days.. What a stupid mistake.. Thanks for your helps..
Gomathi Palaniswamy15y ago
Hi,

check the below code...and what is "frm.serialPort1.Write(sth);"

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 Forum_Q
{
    public partial class Form1 : Form
    {
        mySerial newSerial;
        public Form1()
        {
            InitializeComponent();
        }



        private void Form1_Load(object sender, EventArgs e)
        {


           newSerial = new mySerial(this);

            newSerial.sendData();
        }

        private void button1_Click_1(object sender, EventArgs e)
        {
            newSerial = new mySerial(this);
            newSerial.sendData();
            // THIS CODE DOES NOT WORK!!!
        }


    }
    public class mySerial // this class created by me
    {
        private Form1 frm;

        public mySerial(Form1 newFrm)
        {
            this.frm=newFrm;
        }

        public void sendData()
        {

             frm.serialPort1.Write(sth);
        }

      // I can't reach Form1 controls from this class.
    }


}
Amit Choudhary15y ago
send the object into function as parameter newSerial.sendData(this);
ra change the signature of function remove the code from the class mySerial constructor.

public void sendData(Form1 prntForm)
{
prntForm.serialPort1.Write(sth);
}

If should work. Try it.
Vulpes15y ago
The problem is this line in Form1_Load:

mySerial newSerial = new mySerial(this); newSerial.sendData(); // assigning to local variable

Although it's working OK, the problem is that it's assigning a reference to the new mySerial object to a local variable called 'newSerial' - not to the field (i.e. form level) variable 'newSerial' of the same name which therefore is still null (its default value).

If you change the line as follows then all should be well:

newSerial = new mySerial(this); newSerial.sendData(); // now assigning to field