Question

I’m trying to figure out what is the difference between:

public partial class TestWindow : Window
{
    object obj = new object();
    public TestWindow()
    {
        InitializeComponent();
    }
    private void Window_Loaded(object sender, RoutedEventArgs e)
    {

    }
}

and:

public partial class TestWindow : Window
{
    object obj;
    public TestWindow()
    {
        InitializeComponent();
        obj = new object();
    }
    private void Window_Loaded(object sender, RoutedEventArgs e)
    {

    }
}

and:

public partial class TestWindow : Window
{
    object obj;
    public TestWindow()
    {
        InitializeComponent();

    }
    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        obj = new object();
    }
}

it looks like they all act the same and i wonder if there’s any important difference between them, or is it just a “best practice” thing to choose one of them.
Thanks in advance

Answer 1

The answer to your question is you should initialize variables before you use them.

Field initializers run before constructors, and constructors run before any other method, such as your Window_Loaded. It matters because if you try to use your object before it is initialized, you will get a NullReferenceException. If you don’t use your object before Window_Loaded is called, then it makes no difference.