Communicate between two windows forms in C#

Question

I have two forms, one is the main form and the other is an options form. So say for example that the user clicks on my menu on the main form: Tools -> Options

Answer 1

There are lots of ways to perform communication between two Forms. Some of them have already been explained to you. I am showing you the other way around.

Assuming you have to update some settings from the child form to the parent form. You can make use of these two ways as well :

1. Using System.Action (Here you simply pass the main forms function as the parameter to the child form like a callback function)
2. OpenForms Method ( You directly call one of your open forms)

Using System.Action

You can think of it as a callback function passed to the child form.

// -------- IN THE MAIN FORM --------

// CALLING THE CHILD FORM IN YOUR CODE LOOKS LIKE THIS
Options frmOptions = new Options(UpdateSettings);
frmOptions.Show();

// YOUR FUNCTION IN THE MAIN FORM TO BE EXECUTED
public void UpdateSettings(string data)
{
   // DO YOUR STUFF HERE
}

// -------- IN THE CHILD FORM --------

Action UpdateSettings = null;

// IN THE CHILD FORMS CONSTRUCTOR
public Options(Action UpdateSettings)
{
    InitializeComponent();
    this.UpdateSettings = UpdateSettings;
}

private void btnUpdate_Click(object sender, EventArgs e)
{
    // CALLING THE CALLBACK FUNCTION
    if (UpdateSettings != null)
        UpdateSettings("some data");
}

OpenForms Method

This method is easy (2 lines). But only works with forms that are open. All you need to do is add these two lines where ever you want to pass some data.

Main frmMain = (Main)Application.OpenForms["Main"];
frmMain.UpdateSettings("Some data");