C#

1. SomeClass is a Control (inherited from PictureBox) that exposes public events:
   you can just subscribe to the mousedown event in the MainForm class (just as you set its location):

public class MainForm : Form
{
    // ...

    public MainForm()
    {   
        // ...
        someObject.MouseDown += mouseDown;
    }

    private void mouseDown(object sender, MouseEventArgs e)
    {
        panel1.BackColor = Color.Red;
    }
}

public class SomeClass : PictureBox
{
    Panel panel1;

    public SomeClass(Panel mainPanel)
    {
        panel1 = mainPanel;
        //...
    }
}

SomeClass someObject = new SomeClass(panel1);

public class SomeClass : PictureBox
    {
    public SomeClass()
        {
        this.BackColor = Color.Green;
        this.MouseDown += new System.Windows.Forms.MouseEventHandler(mouseDown);
        }
    public void mouseDown(object sender, MouseEventArgs e)
        {
        OnFocussed(e);
        }
    /// <summary>
    /// Event to indicate Focussed on
    /// </summary>
    public event EventHandler Focussed;
    /// <summary>
    /// Called to signal to subscribers that Focussed on
    /// </summary>
    /// <param name="e"></param>
    protected virtual void OnFocussed(EventArgs e)
        {
        EventHandler eh = Focussed;
        if (eh != null)
            {
            eh(this, e);
            }
        }
    }

    {
    MyPictureBox1.Focussed += MyPictureBox_Focussed;
    MyPictureBox2.Focussed += MyPictureBox_Focussed;
    MyPictureBox3.Focussed += MyPictureBox_Focussed;
    }

void MyPictureBox_Focussed(object sender, EventArgs e)
    {
    SomeClass sc = sender as SomeClass;
    if (sc != null)
        {
        BackColor = Color.Red;
        }
    }

using System;
using System.Drawing;
using System.Windows.Forms;

namespace CPWorking
{
    public partial class PBX : PictureBox
    {
        public PBX()
        {
            InitializeComponent();

            this.BackColor = Color.Green;

            this.MouseDown += OnMouseDown;
        }

        private void OnMouseDown(object sender, MouseEventArgs mouseEventArgs)
        {
            this.Parent.BackColor = Color.Red;
        }
    }
}

public partial class PBX : PictureBox
{
    public PBX()
    {
        InitializeComponent();
        this.MouseDown += OnMouseDown;
    }

    public Action<string, Color> PBXOnColorChanged { set; get; }

    private void OnMouseDown(object sender, MouseEventArgs mouseEventArgs)
    {
        // always check to be sure "something is listening" !
        if (PBXOnColorChanged != null) PBXOnColorChanged((sender as PBX).Name, this.BackColor);
    }
}

private void Form1_Load(object sender, EventArgs e)
{
    pictureBox1.PBXOnColorChanged += PbxOnColorChanged;
    pictureBox2.PBXOnColorChanged += PbxOnColorChanged;
    pictureBox3.PBXOnColorChanged += PbxOnColorChanged;
}

private void PbxOnColorChanged(string pbxName, Color pbxBackColor)
{
    // do something with the data in 'pbxName and 'pbxBackColor

}

public partial class PBX : PictureBox
{
    public PBX()
    {
        InitializeComponent();
        this.BackColor = Color.Green;
        this.MouseDown += OnMouseDown;
    }

    public Func<string, Color, Color> PBXOnColorChanged { set; get; }

    private void OnMouseDown(object sender, MouseEventArgs mouseEventArgs)
    {
        if (PBXOnColorChanged != null)
        {
            Color result = PBXOnColorChanged((sender as PBX).Name, this.BackColor);

            if (result != this.BackColor && result != Color.Empty)
            {
                this.BackColor = result;
            }
            else
            {   // switch it back to green
                this.BackColor = Color.Green;
            }
        }
    }
}

private Color PbxOnColorChanged(string pbxName, Color pbxBackColor)
{
    Color NextColor = Color.Empty;

    switch (pbxName)
    {
        case "pictureBox1":
            if (pbxBackColor == Color.Green) NextColor = Color.Yellow;
            break;
        case "pictureBox2":
            if (pbxBackColor == Color.Green) NextColor = Color.Red;
            break;
        case "pictureBox3":
            break;
    }

    return NextColor;
}

Peter Vegter wrote:

Is there a reason you don't just subscribe to the 'original' event (MouseDown)?

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netstandard1.4</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.Collections.Immutable" Version="1.4.0" />
    <PackageReference Include="System.Net.Sockets" Version="4.3.0" />
    <PackageReference Include="System.ValueTuple" Version="4.4.0" />
    <PackageReference Include="System.Interactive.Async" Version="3.1.1" />
    <PackageReference Include="System.Reactive.Core" Version="3.1.1" />
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\..\Galador.Reflection\Galador.Reflection.PCL\Galador.Reflection.PCL.csproj" />
  </ItemGroup>

</Project>

Super Lloyd wrote:

And also updated them to lastest .csproj format

static class Program
{
    [STAThread]
    static void Main(string[] args)
    {
        bool withoutActivation = false;
        if (args.Length > 0 && !String.IsNullOrWhiteSpace(args[0]))
            withoutActivation = args[0] == "1";

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1(withoutActivation));
    }
}

public partial class Form1 : Form
{
    private bool WithoutActivation;

    public Form1(bool withoutActivation)
    {
        WithoutActivation = withoutActivation;

        InitializeComponent();

        // I placed a lone label on the form:
        label1.Text = WithoutActivation ? "without activation" : "with activation";
    }

    protected override bool ShowWithoutActivation
    {
        get
        {
            return WithoutActivation;
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        bool withoutActivation = false;
        while (!Console.KeyAvailable)
        {
            Thread.Sleep(3000);
            Process.Start("[path to forms-app.exe goes here]", withoutActivation ? "1" : "0");
            withoutActivation = !withoutActivation;
        }
    }
}

e.BringToForeground = false;

using System;
using System.Windows.Forms;
using System.Linq;
using Microsoft.VisualBasic.ApplicationServices;

namespace FileArranger
{
	/// <summary>
	/// Class with program entry point.
	/// </summary>
	
	internal sealed class Program
	{
		/// <summary>
		/// Program entry point.
		/// </summary>
		/// 

		[STAThread]
		static void Main()
		{
			Application.EnableVisualStyles();
			Application.SetCompatibleTextRenderingDefault(false);
			
			string[] args = Environment.GetCommandLineArgs();
			var controller = new SingleInstanceController();
			controller.Run(args);
		}
	}
	
	public class SingleInstanceController : WindowsFormsApplicationBase
	{
		public SingleInstanceController()
		{
			IsSingleInstance = true;
			StartupNextInstance += StartedAgainInstance;
		}
		
		void StartedAgainInstance(object sender, StartupNextInstanceEventArgs e)
		{
			var form = MainForm as MainForm;
			e.BringToForeground = false;
			form.ReadArguments(e.CommandLine.ToArray());
		}
		
		protected override void OnCreateMainForm()
		{
			MainForm = new MainForm();
		}
	}
}