"Object reference not set..." exception when adding control to another form

Question

I'd like to add a UserControl (UserControl2) to a panel on another form (MainForm) when the user clicks a button on the UserControl that is currently in the panel (UserControl1). UserControl2 should replace UserControl1 as the contents of the panel when this button is clicked.

I've tried figuring out how to use an event to communicate between UserControl1 and MainForm, but I just don't know where to start, as I can't find an example that is easily adaptable to my particular situation (Adding a control to a panel).

THIS question is similar, but doesn't quite fit what I'm trying to do (or at least I just don't know how to adapt it to what I'm trying to do)

I've tried this method, and get no errors, but my button doesn't do anything:

MainForm:

    private void SubscribeToEvent(MyUserControl1 Button_Click)
    {
        MyUserControl1 CurrentClass = new MyUserControl1();
        CurrentClass.Button.Click += new EventHandler(this.ButtonClickHandler);
    }

    private void ButtonClickHandler(object sender, EventArgs e)
    {
        MyUserControl2 MainPanelControls = new MyUserControl2();
        MainPanel.SuspendLayout();
        MainPanel.Controls.Clear();
        MainPanel.Controls.Add(MainPanelControls);
        MainPanel.ResumeLayout();
    }

UserControl1:

    public void Button_Click(object sender, EventArgs e)
    {
        //... Not sure what I'm missing here
    }

---

I've also tried this method, this time trying to implement something similar to the method described in the link near the top of my question. I know these are obviously wrong (otherwise I wouldn't need to ask the question), but I don't have enough knowledge on the subject to figure it out on my own:

UserControl1:

    public MyUserControl1()
    {
        InitializeComponent();
    }

    private MainForm mainForm = null;
    public MyUserControl1(Form callingForm)
    {
        mainForm = callingForm as MainForm;
        InitializeComponent();
    }

//...

    private void Button_Click(object sender, EventArgs e)
    {
        MyUserControl2 MainPanelControls = new MyUserControl2();
        mainForm.MainPanel.SuspendLayout();
        mainForm.MainPanel.Controls.Clear();
        mainForm.MainPanel.Controls.Add(MainPanelControls);
        mainForm.MainPanel.ResumeLayout();
    }

Now when I click Button I get an "Object reference not set to an instance of an object" error at mainForm.MainPanel.SuspendLayout(); (Or anything past that point).

I've also tried modifying Joh's answer, but end up with the same Null Reference Exception, this time on my Button_Click event at ButtonClickedToMainForm(this, e); I'm not sure if I need to create an instance of ButtonClickedToMainForm, or how to do that properly (if it's not something else, that is).

I have a feeling I've likely just placed some of this code in the wrong place, so I'm hoping someone more experienced may be able to help me sort that out.

UPDATE

This is my attempt at implementing Joh's answer, being so new to this, I'm not quite sure where I've messed up:

MainForm:

namespace MyProject
{
public delegate void ButtonClickToMainForm(object sender, EventArgs e);

public partial class MainForm : Form
{

    public MainForm()
    {
        InitializeComponent();
        UserControl1 userControl1 = new UserControl1();
        userControl1.Button1Clicked += userControl1_Button1Clicked;
    }

    private void userControl1_Button1Clicked(object sender, EventArgs e)
    {
        try
        {
            UserControl2 MainPanelControls = new UserControl2();
            MainPanel.SuspendLayout();
            MainPanel.Controls.Clear();
            MainPanel.Controls.Add(MainPanelControls);
            MainPanel.ResumeLayout();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }
  }
}

UserControl1:

public partial class UserControl1: UserControl
{
    public event ButtonClickToMainForm Button1Clicked;

    public UserControl1()
    {
        InitializeComponent();
    }

    private void OnButton1Clicked(object sender, EventArgs e)
    {
        Button1Clicked?.Invoke(this, e);
    }

    private void Button1_Click(object sender, EventArgs e)
    {
        Button1Clicked(this, e);  //"Object reference not set to an instance of an object."
    }
}

I'm sure it's something simple I'm missing on UserControl1, I'm just not sure what.

Answer 1

Here is an easy example for a delegate event.When you implement it in all your usercontrols it should work for your problem.

UserControl:

//Create a delegate
    public delegate void ButtonClickToMainForm(object sender, EventArgs e);

    public partial class UserControl1 : UserControl
    {
        //Your own event based on created delegate
        public event ButtonClickToMainForm ButtonClickedToMainForm;

        public UserControl1()
        {
            InitializeComponent();
        }

       //This method will invoke your event
        private void OnButtonClickedToMainForm(object sender, EventArgs e)
        {
            ButtonClickedToMainForm?.Invoke(this, e);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //On button1_Click this will fire the event on mainform
            OnButtonClickedToMainForm(this, e);
        }

and the mainForm :

 public Form1()
        {
            InitializeComponent();
            //Subscribe to event from your usercontrol
            userControl11.ButtonClickedToMainForm += UserControl11_ButtonClickedToMainForm;
        }

        //Button on userControl1 has been clicked
        private void UserControl11_ButtonClickedToMainForm(object sender, EventArgs e)
        {
            //do your things here...
        }

Hope this helps.