Call a function from another form

Question

I have a form MainForm and a form form1, declared like this:

namespace SdkDemo
{
    public partial class MainForm : Form
    {        
        public CoreWrapper _icCore;        
        private Dictionary<string, int> audioDevices;

        #region MainForm Ctor

        public MainForm()
        {
            InitializeComponent();
            _icCore.Start();
        }

        public Form1 form1 = new Form1();
    }
}

So form1 is just created with Visual Studio tools.

The whole code of form1:

namespace SdkDemo
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();            
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string dial = Registry.CurrentUser.OpenSubKey("SOFTWARE").OpenSubKey("CS").GetValue("DIAL").ToString();

            // Error "An object reference is expected":
            MainForm.txtSendKeys.Text = ("esdcze");
        }        
    }
}

The problem is that an object reference error appears when i try to call something in "Mainform". Of course, the txtSendKeys field is public.

BTW, I can easily do the reverse action, which is to do something like

MainForm.textField = x

from my form1.

I seriously lack of knowledge about C#, but this one is for my work and I start to desperate by now..

See: http://stackoverflow.com/questions/6803970/access-form-component-from-another-class?rq=1 — KingCronus, May 31 '13 at 10:28
you have to call an instance of MainForm not the "Public" UI element. Add a MainForm object inside the Form1 and pass the MainForm instance that is already created. Then call the instance to edit the UI element. — Emmanouil Chountasis, May 31 '13 at 10:29

KingCronus · Accepted Answer · 2013-05-31T12:06:28.453

MainForm is the definition of a form, not an Instance of it. Also you don't appear to be showing Form1 anywhere, so I have added that to MainForm.Load for now, but obviously you could move that.

You need to try something more like this:

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

    public MainForm MyParentForm { get; set; }       

    private void button1_Click(object sender, EventArgs e)
    {
        string dial = Registry.CurrentUser.OpenSubKey("SOFTWARE").OpenSubKey("CS").GetValue("DIAL").ToString();

        // Use the reference to MyParentForm
        MyParentForm.txtSendKeys.Text = "esdcze";
    }        
}

Then in your Main:

public partial class MainForm : Form
{        
    public CoreWrapper _icCore;        
    private Dictionary<string, int> audioDevices;

    #region MainForm Ctor

    public MainForm()
    {
        InitializeComponent();
        _icCore.Start();
    }

    private void MainForm_Load(object sender, System.EventArgs e)
    {
        form1.MyParentForm = this;
        form1.Show();
    }

    public Form1 form1 = new Form1();
}

It is very important to make sure that you set the "MyParentForm" property before you use it in Form1. Form1 will throw an exception if not. A more clever way might involve checking the property isn't Null first.

Thank you for your help! Yet it throws me an exception "The object reference is not defined to an object instance", when it comes to line "MyParentForm.txtSendKeys.Text" — Grigory Kornilov, May 31 '13 at 12:00
Hi, in the designer, make sure that MainForm.cs has the Load event set to the correct method. — KingCronus, May 31 '13 at 12:07
Peanuts price! It works! In the designer, I put "form1_load" to "Load" event, and it works. Thank you multiple times! — Grigory Kornilov, May 31 '13 at 12:26

score 0 · Answer 2 · answered May 31 '13 at 10:43

Modify your MainForm class:

public partial class MainForm : Form
{
    public CoreWrapper _icCore;
    private Dictionary<string, int> audioDevices;

    public MainForm()
    {
        InitializeComponent();
        _icCore.Start();
        // sets the form1's owner form to the MainForm instance
        form1.Owner = this;
        // show the Form1 form
        form1.Show();
    }

    public Form1 form1 = new Form1();

    internal void SetSendKeys(string value)
    {
        txtSendKeys.Text = value;
    }
}

Modify your Form1.button1_Click method's body:

private void button1_Click(object sender, EventArgs e)
{
    string dial = Registry.CurrentUser.OpenSubKey("SOFTWARE").OpenSubKey("CS").GetValue("DIAL").ToString();
    var mainForm = (MainForm)this.Owner;
    mainForm.SetSendKeys("esdcze");
}

Call a function from another form

2 Answers2