How can I access the MainForm from within a class in a separate project?

Question

I have two projects in this solution: ProjectA and ProjectB. ProjectA is the main start-up project, and has a reference to ProjectB.

ProjectA has a file called MainForm.cs, which contains a textbox and the main UI.

ProjectB has a class inside Shapes.cs, containing a particular structure we're using. Shapes.cs contains an event that is fired when the user changes some text for that object.

What I need to do is catch that text and set a textbox in MainForm.cs to that text. Is there a way we can do that? Basically I don't see any reference to the main form inside Shapes.cs. I would like to do something like this:

( Shape1.Parent as MainForm ).TextBox1.Text = Shape1.Name;

, assuming the user types a string that gets stored in Shape1.Name. I need to escalate it to the main form.

I have searched around for other questions, and the closest lead I found was Matt Hamsmith's answer on this question. But if it is a good approach I should follow, I do not know how to assign an event handler in the main form to an event in the separate class. I would appreciate any help.

Thanks.

Answer 1

If the form is made up child controls, it should be listening to events on those controls, rather than the controls trying to cast their parent as a particular type. Doing that means your control will only ever work on that Form. It breaks encapsulation.

Listen to an event like this:

public class MainForm : Form
{
    Shape _shape1 = new Shape();

    public MainForm()
    {
        InitializeComponent();
        _shape.ShapeNameChanged += HandleShapeNameChanged;
    }

    public void HandleShapeNameChanged(object sender, ShapeChangeEventArgs e)
    {
        textBox1.Text = e.NewName;
    }
}

public class Shape
{
    public event EventHandler<ShapNameChangedEventArgs> ShapeNameChanged;
}

I've left it for you to:

1. Define the ShapeNameChangedEventArgs object to contain whatever state you want it to.
2. Invoke the event when something on your control changes.

Good luck!