C# Unable to obtain value (a score) from another class

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C#

Hello reader,

I'm trying to make a little puzzle game "Connect the dots".
And I have the following problem:
What I'm trying to do is to get a score value (property ScoreCounter(in class Grid.cs)) on my form (most likely showable with a label).
I tried to make scoreCounter public just to test it out, and I also tried to make a property which didn't work aswell.
I tried debugging and I saw that when the player is suppose to obtain a point when crossing a dot the value of scoreCounter actually increments within the condition.
But when I place a breakpoint at the top where I declared the score, it tells me it has no value.
Could someone please help me to obtain the score so I can display it in a label?
Many thanks in advance!
Debug example


This is how the code looks like:

At the top of the class Form

private Grid drawing;

Somewhere in the class Form

lblScore.Text = "Score: " + Convert.ToString(drawing.ScoreCounter);

Class Grid.cs

private int scoreCounter;
public int ScoreCounter
{
    get { return scoreCounter; }
    set { scoreCounter = value; }
}


protected override void OnMouseUp(MouseEventArgs e)
{
    base.OnMouseUp(e);  //On Panel
    var dotLocation = this.GetDotFromPoint(e.Location); //checks if graphic location is a dot

    // If the first holded dot is color green
    if (lastDot.DotColor == colorGreen)
    {
        firstGreen = true;
    }

    if (firstGreen)
    {
        // Checks if MouseUp is on a dot that isn't colored red
        // Checks if the user doesn't skip a dot
        // Checks if the user doesn't cross a dot diagonally (only allows horizontally)
        if (dotLocation != null && lastDot != null && dotLocation.DotColor != colorRed &&
       ((lastDot.Center.X + 40 == dotLocation.Center.X) || (lastDot.Center.X - 40 == dotLocation.Center.X)) &&
       (lastDot.Center.Y == dotLocation.Center.Y))
        {

            scoreCounter += 1;
            Line line = new Line();
            line.X1 = lastDot.Center.X;
            line.Y1 = lastDot.Center.Y;

            line.X2 = dotLocation.Center.X;
            line.Y2 = dotLocation.Center.Y;
            this.markers.Add(line);
            Invalidate();
        }

        // Checks if MouseUp is on a dot that isn't colored red
        // Checks if the user doesn't skip a dot
        // Checks if the user doesn't cross a dot diagonally (only allows vertically)
        else if (dotLocation != null && lastDot != null && dotLocation.DotColor != colorRed &&
            ((lastDot.Center.Y + 40 == dotLocation.Center.Y) || (lastDot.Center.Y - 40 == dotLocation.Center.Y)) &&
            (lastDot.Center.X == dotLocation.Center.X))
        {
            scoreCounter += 1;
            Line line = new Line();
            line.X1 = lastDot.Center.X;
            line.Y1 = lastDot.Center.Y;

            line.X2 = dotLocation.Center.X;
            line.Y2 = dotLocation.Center.Y;
            this.markers.Add(line);
            Invalidate();
        }
        else
        {
            MessageBox.Show("Invalid turn, try again.");
        }
    }
}

I also have the idea that whatever I'm trying to in the Form like for example calling a method in the class Grid it doesn't work.
I tested it by trying to clear the list markers by doing the following thing:

In Form calling the following method

drawing.ClearLines();

And in class Grid.cs

public void ClearLines()
{
    markers.Clear();
    scoreCounter = 0;
    Invalidate();
}

I also called the same method in the method OnMouseUp

else
{
    MessageBox.Show("Invalid turn, try again.");
    ClearLines() // or markers.Clear();
}

It all doesn't work.