C# from winform application how to open another winform application and send value to it?

Question

I have 2 winform applications, say form1 and form2 .

They are programmed through separate visual studio programs

form1 is programmed in WindowsFormsApplication1.sln

form2 is programmed in WindowsFormsApplication2.sln

I want to open form2 (=WindowsFormApplication2.exe) by clicking a button in form1

I created a method in WindowsFormApplication1.sln

private void button3_Click(object sender, EventArgs e)    
{
     var p = new Process();
     p.StartInfo.FileName ="WindowsFormsApplication2.exe";
     p.StartInfo.Arguments = "10";
     p.Start();
}

This method opens WindowsFormApplication2.exe

Then I need WindowsFormApplication2 MessageBox show the value got from WindowsFormApplication1.exe. Is this clear?

This should be clear... I cannot explain more simply than this

---

What other people have answered through comment or answerbox, is not what I want

If I want to pass a value from form1 to form2 that are in same .sln (That is, WindowsFormApplication1.sln has form1 and form2), this is so easy

I could just use

Form2 form2 = new Form2(textBox1.Text);    
form2.Show();

Constructor Form2 :

public Form2(string smth)    
{
     InitializeComponent();
     label1.Text = smth;
}

But this is not what I want

I think everything is clear. Please tell me how to solve the problem

Answer 1

C# programs have a static void Main() method that is the entry point for the application. You should see something like this in your Program.cs file in your winform2 project:

/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    Application.Run(new Form1());
}

If you want to enable your winform2 application to accept command-line arguments, you capture them from this method. But first you need to modify the method signature to take in a string[] of arguments:

// Add a string[] argument to the Main entry point method
static void Main(string[] args)

Now any command line arguments passed to this application will be in the args array.

Next, we need to modify your winform2 application's main form constructor to take in one or more string arguments, so we can pass them in the line that says Application.Run(new Form1()) .

For example, you can modify your form's constructor to take in a string (I'm using Form1 as an example):

public partial class Form1 : Form
{
    // Add a string argument to the form's constructor. 
    // If it's not empty, we'll use it for the form's title.
    public Form1(string input)
    {
        InitializeComponent();

        if (!string.IsNullOrEmpty(input)) this.Text = input;
     }
}

After we enable the form to take a string input, we now modify the call to the constructor to pass a string to our form. In this case, I'm expecting a string like: /Title:"Some Form Title" , so I'll look at the args array and try to find a match.

static void Main(string[] args)
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    // Try to find the 'Title' argument
    var titleArg = args?.FirstOrDefault(arg => arg.StartsWith("/Title:", 
        StringComparison.OrdinalIgnoreCase));

    // Now strip off the beginning part of the argument
    titleArg = titleArg?.Replace("/Title:", "");

    // And now we can pass this to our form constructor
    Application.Run(new Form1(titleArg));
}

Now you can launch your WinForm application from the command line and pass in a string, which will become the title. Here I'm running the .exe from the command line and passing /Title:"Custom Title From Command Line" , but you could just assign this string to the Arguments property of your ProcessStartInfo instance if you're launching the application programmatically.: