C# Take combobox item from one form and add its name as text to another

Question

Ok so I'm attempting to create a simple game. In a nutshell it's a resource management game where the player will attempt to manage a thieves guild. In regards to running missions I've created a Thief class, a new instance of which is created when a new thief is recruited. I have coded within the thief class the ability to gain experience and level up.

Here's my specific problem: I want the player to be able to select which thief/thieves to send on a mission. I have thought about it and figured that opening a new form and populating it with checkboxes is the easiest way to allow this. These checkboxes will be related to a List<thief> of thieves, the player then checks the thieves s/he wants to send and these are then stored in another List<thief> and passed on to the run mission function.

I've built a separate project with the intention of testing and playing around with this before putting it into the main program. The test project consists of two forms: The first (frmMain) with a textbox to hold the selected options and a button to open the second form (frmSelect). Currently I can open and populate the second form (frmSelect) but when I try to add the checked options to the textbox I simply...well can't.

So far I have tried directly accessing the textbox by typing frmMain.txtOptionsDisplay in the cs file of frmSelect but it causes the following error:

An object reference is required for the non-static field, method or property

I tried to create a new form in frmSelect and make it equal to the active instance of frmMain with: Form frmTemp = frmMain.ActiveForm; and then alter the textbox using frmTemp as a go-between but that produced the error:

'System.Windows.Forms.Form' does not contain a definition for 'txtOptionsDisplay'.

Having searched both google and stackoverflow forums I've encountered answers that I either have never heard of (Threading) or answers that I kind've recognise but can't interpret the code pasted to make it relevant to my problem (delegates).

Any advice or pointers would be fantastic.

EDIT: frmMain code:

    public frmMain()
    {
        InitializeComponent();
        selections.Add("Option 1");
        selections.Add("Option 2");            
    }

    private void btnClick_Click(object sender, EventArgs e)
    {            
        frmSelectOptions.Show();

        int length = selections.Count();
        for (int i = 0; i < length; i++)
        {
            CheckBox box = new CheckBox();
            box.Text = selections[i];
            box.AutoSize = true;
            box.Location = new Point(50, 50*(i+1));
            frmSelectOptions.grpControls.Controls.Add(box);
        }
    }
    public void updateText(string option)
    {
        txtOptionsDisplay.Text += option;
    }
}

frmSelect code:

    public List<CheckBox> selectedOptions = new List<CheckBox>();

    Form frmTemp = frmMain.ActiveForm;

    public frmSelect()
    {
        InitializeComponent();
    }

    private void btnSelect_Click(object sender, EventArgs e)
    {
        foreach (CheckBox box in grpControls.Controls)
        {
            if (box.Checked == true)
                selectedOptions.Add(box);
        }

        this.Hide();
    }

}

I hope this formats correctly... I'm kinda new and don't know how to indent. Oh look there's a preview...

Does this help?

Answer 1

Your problem is that controls defined within a form by default receive the private access identifier. Hence you could just add a property along the lines of

public ControlType ProxyProperty {
  get {
   return txtOptionsDisplay;
  }
}

Besides from that you should think about wether what you're trying is actually a good solution. Manipulating forms from one to another will become a huge clusterfuck in terms of maintenance later on.

Answer 2

I'd suggest using the Singleton pattern for your frmMain. This will help safeguard you from accidentally launching another instance of frmMain and at the same time, will give you access to frmMain's objects. From there, you can either write accessors to Get your txtOptionsDisplay or you can make it public. Below is an example:

public class frmMain
{
    private static frmMain Instance = null;
    private static object LockObj = new object();

    public static frmMain GetMain()
    {
        // Thread-safe singleton
        lock(LockObj)
        {
            if(Instance == null)
                Instance = new frmMain();

            return Instance;
        }
    }

    public string GetOptionsDisplayText()
    {
        return txtOptionsDisplay.Text;
    }
}

public class frmSelect
{
    private void frmSelect_Load(object sender, EventArgs e)
    {
        // Set whatever text you want to frmMain's txtOptionsDisplay text
        txtDisplay.Text = frmMain.GetMain().GetOptionsDisplayText();
    }
}

If you do go this route, don't forget to update Program.cs to use frmMain's singleton.

    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        // Application.Run(new frmMain()); - Old method
        Application.Run(frmMain.GetMain());
    }