NullReferenceException when trying to set class property

Question

Basically I have 2 classes, \"Manifest\" and \"BrowserAction\", set out like this:

public class BrowserAction
{
    public string default_icon {get; set;}
    pu         


        

Answer 1

You've initialised newManifest, but browser_action is still null (presumably).

You are then trying to set default_popup on the null browser_action and getting the exception

newManifest.browser_action.default_popup = "popup.html";

Answer 2

Default value for reference-type object is null. You need to create BrowserAction instance on browser_action property before using it.

// Create Manifest instance
Manifest newManifest = new Manifest();

Console.Writeline (newManifest.browser_action == null); // Print true;

// Instantiate BrowserAction on browser_action property
newManifest.browser_action = new BrowserAction();

Console.Writeline (newManifest.browser_action == null); // Print false;

// Now you can use browser_action property
newManifest.browser_action.default_popup = "popup.html";

Answer 3

I think the Manifest.browser_action property returns null because you don't initialize it. Create an object before accessing its properties:

Manifest newManifest = new Manifest();
newManifest.browser_action = new BrowserAction();
newManifest.browser_action.default_popup = "popup.html";

Answer 4

You are accessing property browser_action of newly created instance newManifest that is still null.

Change your example to something like:

public void setManifest()
{
    Manifest newManifest = new Manifest();
    newManifest.browser_action = new BrowserAction();
    newManifest.browser_action.default_popup = "popup.html";
}

I am assuming that BrowserAction has a public accessible constructor with no arguments.

Or in one go:

public void setManifest()
{
    Manifest newManifest = new Manifest()
        {
            browser_action = new BrowserAction()
                {
                    default_popup = "popup.html"
                }
        };
}

Answer 5

browser_action has not been initialized. Add a parameterless constructor to your Manifest class like this:

public class Manifest
{
    public Manifest()
    {
           this.browser_action = new BrowswerAction;
    }

    public BrowserAction browser_action {get; set;}
}

Answer 6

You'll have to intialize browser_action too before accessing properties on that instance.

newManifest.browser_action= new BrowserAction();