asked on

Rookie question from java programmer

so i am trying to do a basic C# windows application.
I have a form that calls another form (Modal)
The settings form needs to access some vars from the parent form
So i am not sure the best way , but i thought i would try this::

SettingsForm settingsForm = new SettingsForm();
settingsForm.setParent(this);
settingsForm.ShowDialog();

then in the settings form i tried::

public void setParent(Form1 form1)
{
this.parent = form1;
}

public SettingsForm()
{
InitializeComponent();
tbServerURL.Text = parent.ServerURL;
tbDatFileLocation.Text = parent.DataSourceLocation;
}

When i call the method that opens the modal form i get the error:::

System.NullReferenceException was unhandled
Message=Object reference not set to an instance of an object.

I am sure this is some very rookie misunderstanding of the language.
Any help would be appreciated

Thanks

Todd Gerbert

The constructor for your settings form:

public SettingsForm()
        {
            InitializeComponent();
            tbServerURL.Text = parent.ServerURL;
            tbDatFileLocation.Text = parent.DataSourceLocation;
        }

Open in new window

Is executed when it's instantiated with the SettingsForm settingsForm = new SettingsForm() line, and is making references to parent before your call to setParent.

Try passing the reference to the parent in the SettingsForm's constructor.

SettingsForm settingsForm = new SettingsForm(this);
settingsForm.ShowDialog();

Open in new window

public class SettingsForm : Form
{
  private Form1 parent;
  public SettingsForm(Form1 parent)
  {
    InitializeComponent();
    this.parent = parent;
    tbServerURL.Text = parent.ServerURL;
    tbDatFileLocation.Text = parent.DataSourceLocation;
  }
}

Open in new window

jdavistx

The reason you received that error is because you're setting the parent after the new Settings form has already been instantiated. Try this instead:

//In Form1
SettingsForm settingsForm = new SettingsForm();
settingsForm.ShowDialog();

//In SettingsForm
public SettingsForm(Form1 form1)
{
	InitializeComponent();
	this.parent = form1;
	tbServerURL.Text = parent.ServerURL;
}

Open in new window

However, passing the entire form object may not be the most practical solution to retrieve the values. A common method for using "global" variables is to create a static class, and use it for your variables that will be used across different forms.

http://msdn.microsoft.com/en-us/library/79b3xss3(v=VS.100).aspx

jdavistx

Ah, I forgot the form in the SettingsForm(this) call, but tgerbert's comment has it in there.

paries

ASKER

thats for the response

that is what i did when i originally called settingsForm.Show(this);

but when i changed to settingsForm.ShowDialog(this); (cause i want it to be modal)

it still only calls public SettingsForm()

I set my breakpoint in both

SOLUTION

Todd Gerbert

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ASKER CERTIFIED SOLUTION

jdavistx

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