NullReferenceException was unhandled, Object Reference not set to an instance of an object

Question

Hi there, Whenever I run my program, I get: NullReferenceException was unhandled, Object Reference not set to an instance of an object.

When I start the program, I have a form appear called MaxScore where the user enters the max score and presses OK. In the OK event, I call a method from MainForm to update the maxGameCountLabel on MainForm with the value entered for the max score, as a parameter.

When I press ok, I get the NullReferenceException at

myGameCountLbl.Text = maxGames.ToString();

of my maxGameCountLblUpdate method.

Here is the maxGameCountLblUpdate method code which resides in MainForm:

//Update game count label 
public void maxGameCountLblUpdate(decimal maxGames)
{
    maxGames = decimal.ToInt32(maxGames);
    myGameCountLbl.Text = maxGames.ToString();
    compGameCountLbl.Text = maxGames.ToString();
}

Here is my OK Button event on MaxScore:

private void okBtn_Click(object sender, EventArgs e)
{
    MainForm.maxGameCountLblUpdate(max);
}

Note, I have set

public Form1 MainForm { get; set; }

in MaxScore

And I create MaxScore in MainForm with:

    using (MaxScore scoreForm = new MaxScore())
    {
        scoreForm.MainForm = this;
        scoreForm.ShowDialog();
    }

I can't get this to work.. I have tried many things.. Thanks!

EDIT: After adding a breakpoint at myGameCountLbl.Text = maxGames.ToString(); myGameCountLbl appears to be coming up as null... Im sorry for being a newb... How do I fix this? maxGames, indeed, does come up as 1, so that is not the problem

Answer 1

Well if this is the line that's causing the problem:

myGameCountLbl.Text = maxGames.ToString();

then either myGameCountLbl is null, or maxGames is. Given that maxGames is a decimal, that suggests that myGameCountLbl is null.

What happens when you debug into this and put a breakpoint on the appropriate line? What does that show for myGameCountLbl?

Answer 2

Why don't you put a breakpoint in that line and debug the current state of both objects? Where is max coming from in here?

MainForm.maxGameCountLblUpdate(max);

Answer 3

You can also have Visual Studio break on all exceptions, or break on all NullReferenceExceptions, and then you can inspect what's going on.

(Debug -> Exceptions -> Common Language Runtime Exceptions ...)

Answer 4

Did you remove: InitializeComponent(); from the constructor?

If you are using the designer to build the form UI, Visual Studio builds a method in the background (Class.designer.cs) to initialize the controls. If you don't call InitializeComponent() before you access the UI elements, you will get a NullReferenceException.