Passing data to a non-static listBox, by calling function from another class

Question

I have a simple forms program that I have been fighting with for a while now. I simply want to be able to call a method from a different class file (when a certain step is triggered in the code in that class file) in order to insert a string in the listBox.

Here is my main method, pretty standard:

class Program
{
    [STAThread]
    static void Main(string[] args)
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new MainForm());
    }
}

Here is the function which resides in my MainForm.cs file, which I can call just fine from that class file (via 'TextToBox(myString);'):

public partial class MainForm : Form
{
    ...
    // Function to output results to main Listbox window        
    public void TextToBox(string aString)
    {            
        // Place messages in Main Display list box window
        this.listBox1.Items.Insert(0, aString);            
    }
    ...
}

But my problem is when I am in another class and I want to call 'TextToBox(myString);'. If I create another object reference of the MainForm, the code compiles fine but nothing will show up in the listBox. How do I do this? I cannot simply make TextToBox() static. I know I must create the object reference but I can't figure out how to reference the ORIGINAL MainForm, the one that was created in the Main method. Thanks in advance...

Answer 1

I would just pass a delegate to the other class.

/* this runs (previous code was not guaranteed to run) */
class OtherClass
{
    public delegate void TextToBox(string s);

    TextToBox textToBox;
    int next = 0;

    public OtherClass(TextToBox ttb)
    {
        textToBox = ttb;
    }

    public void SendSomeText()
    {
        textToBox(next.ToString());
        next++;
    }
}

I'm assuming you'll be instantiating OtherClass from MainForm. Is this how you're calling "OtherClass"?

public partial class MainForm : Form
{
    OtherClass otherClass;

    public MainForm()
    {
        /* just two controls -- listBox1 and button1 */
        InitializeComponent();
        otherClass = new OtherClass(this.TextToBox);
    }

    public void TextToBox(string aString)
    {
        listBox1.Items.Add(aString);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        otherClass.SendSomeText();
    }
}

On a button click the next numeric value is added at the beginning of the ListBox. You'll have to post some of your code if you need further help.

Answer 2

alternatively you could use a singleton pattern, or static methods and make sure you include the class in a 'using' statement at the top of your program

Answer 3

This will work, but only when you have one instans of MainForm.

public class MainForm : Form
{
    public MainForm()
    {
        Instance = this;
    }

    public static MainForm Instance { get; private set; }

    // Function to output results to main Listbox window        
    public void TextToBox(string aString)
    {
        // Place messages in Main Display list box window
        this.listBox1.Items.Insert(0, aString);
    }

}
public class Other
{
    public void AddTextToListBox()
    {
        MainForm.Instance.TextToBox("Test");
    }
}

...Edit... Alternative:

class Program
{
    public static MainForm MainFormInstance;
    [STAThread]
    static void Main(string[] args)
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        MainFormInstance = new MainForm();
        Application.Run(MainFormInstance);
    }
}

public class Other
{
    public void AddTextToListBox()
    {
        Program.MainFormInstance.TextToBox("Test");
    }
}