Question

in my main form, i have a timer which update the value in the text box every few seconds, the code are the following:

public partial class Form1 : Form
{
    static int column = 2;
    static int row = 100;
    System.Windows.Forms.TextBox[,] textbox = new System.Windows.Forms.TextBox[column, row];

    delegate void StringParameterDelegate(int j, string value);
    DisplayTimer displayTimer = new DisplayTimer();
    System.Threading.TimerCallback displayCallback;
    System.Threading.Timer displayTimerThread;

    public Form1()
    {
        InitializeComponent();

             //set the array for name and update time 

        for (int k = 0; k < column; k++)
        {
            for (int j = 0; j < row; j++)
            {
                textbox[k, j] = new System.Windows.Forms.TextBox();
                textbox[k, j].Size = new Size(160, 18);
                textbox[k, j].Name = "textbox_" + k + "_" + j;

                if (j >= 100)
                {
                    textbox[k, j].Location = new System.Drawing.Point((k * 160) + 20, (j * 18) + 30);
                }

                textbox[k, j].Visible = true;
                Controls.Add(textbox[k, j]);
            }
        }

        displayCallback = new System.Threading.TimerCallback(timeDisplay);
        displayTimerThread = new System.Threading.Timer(displayCallback, displayTimer, 3000, 3000);
                // more code
    }

    public void timeDisplay(object timerObject)
    {
        DisplayTimer t = (DisplayTimer)timerObject;  

        for (int j = 0; j < t.row; j++)
        {
            string value = t.outputTime[j].ToString("yyyy/MM/dd HH:mm:ss.fff");
            writeToTextBox(j, value);
        }
    }

    public void writeToTextBox(int j, string value)
    {
        if (InvokeRequired)
        {
            BeginInvoke(new StringParameterDelegate(writeToTextBox), new object[] { j, value });
            return;
        }
        // Must be on the UI thread if we've got this far
        textbox[1, j].Text = value;
    }

now the above code runs fine and no error occurs. However i have 3 forms in my program use the same method timeDisplay and writeToTextBox, i have to duplicate the code 3 times in the form. I have tried to refactor the 2 methods and put it into a new class. i got the following errors for my writeToTextBox method.

Error 1 The name ‘InvokeRequired’ does not exist in the current
context

Error 2 The name ‘BeginInvoke’ does not exist in the current context

Error 3 The name ‘textbox’ does not exist in the current context

how do i refactor it effectively? some working snippet of code would be very helpful, thanks in advance

EDIT: below is the correct code for the question: it runs fine without any error. Thanks Tudor

class DisplayTimer
{
    public int numberOfRow = 0;
    public int column = 0;
    public DateTime[] outputTime;
    public System.Windows.Forms.TextBox[,] textbox;
    delegate void StringParameterDelegate(TextBox textbox, string value);

    public void timeDisplay(object timerObject)
    {
        DisplayTimer t = (DisplayTimer)timerObject;

        for (int j = 0; j < t.numberOfRow; j++)
        {
            string value = t.outputTime[j].ToString("yyyy/MM/dd HH:mm:ss.fff");

            if (value != "0001/01/01 00:00:00.000")
            {
                writeToTextBox(textbox[column, j], value);
            }
        }
    }

    public void writeToTextBox(TextBox textbox, string value)
    {
        if (textbox.InvokeRequired)
        {
            textbox.BeginInvoke(new StringParameterDelegate(writeToTextBox), new object[] { textbox, value });
            return;
        }
        // Must be on the UI thread if we've got this far
        textbox.Text = value;
    }
}

Answer 1

If you move your method outside the Form1 class you’ll need to add at least the control as a parameter to the method, since BeginInvoke and InvokeRequired are called on this. you can just pass the textbox array and call the invokes on it:

public void writeToTextBox(int j, string value, TextBox[,] textBoxes)
{
    TextBox textBox = textBoxes[1, j];
    if (textBox.InvokeRequired)
    {
        textBox.BeginInvoke(new StringParameterDelegate(writeToTextBox), new object[] { j, value, textBoxes });
        return;
    }
    // Must be on the UI thread if we've got this far
    textBox.Text = value;
}