Instead of adding Mouseclicked as an event handler, you’re calling Mouseclicked and adding what it returns, in this case null as a handler. Removing the (Data.C_Title) is what you want, though it will expose a different problem in this case.

Almost all (if not all) WinForms event handlers are expected to have arguments of (object sender, System.EventArgs e) where EventArgs might be replaced with another class inheriting from EventArgs. So MouseClicked needs to be changed to have those parameters.

• Store Data.C_Title in a field somewhere, and reference that field inside your Mouseclicked event-handler.

  • And Mouseclicked needs to conform to MouseEventHandler, i.e. private void Mouseclicked(Object? sender, EventArgs e).

• Wire-up seriesPanel.MouseClick correctly:

  • If your event-handlers will be added only once, inside the ctor (after InitialzieComponent), then you can use seriesPanel.MouseClick += this.Mouseclicked (this creates a delegate variable behind-the-scenes and passes that to the MouseClick multicast delegate).
  • If your event-handlers are dynamic (added and removed at runtime) then you need to use += and -= with a MouseEventHandler-typed variable rather than the method-name itself.

• Also, are you sure you want MouseClick instead of Click? Consider using Click instead of MouseClick where-possible for accessibility reasons.

Like so:

(I’ve renamed the Mouseclicked method to OnSeriesPanelClicked for clarity)

void Somewhere( ... )
{
    this.title = Data.C._Title;

    // called on creation (I create my control through code so doing it manually wont work)
    seriesPanel.MouseClick += this.OnSeriesPanelClicked;
}

private String? title;

public void OnSeriesPanelClicked(Object? sender, EventArgs e)
{
    SeriePage page = new SeriePage();
    page.Title = this.title;
    page.Show();
}

For added/removed event-handlers (and assuming you’ll be using different handler methods than just OnSeriesPanelClicked):

(For clarity, this code is more verbose than it needs to be)

void Somewhere( ... )
{
    if( this.lastMouseClick != null )
    {
        seriesPanel.MouseClick -= this.lastMouseClickHandler;
        this.lastMouseClickHandler = null;
    }

    this.title = Data.C._Title;

    MouseEventHandler newHandler = new MouseEventHandler( this.OnSeriesPanelClicked );
    seriesPanel.MouseClick += newHandler;
    this.lastMouseClickHandler = newHandler;
}

private MouseEventHandler? lastMouseClickHandler;

private String? title;

public void OnSeriesPanelClicked(Object? sender, EventArgs e)
{
    SeriePage page = new SeriePage();
    page.Title = this.title;
    page.Show();
}