XNA空参考异常

Question

Everything was working fine on this game I am making, but now I started getting NullReferenceException errors on some of my code.

Here I define a Vector2 and a Texture2D:

Vector2 startButtonPosition;
Texture2D startButton;

And then in the Initialise() method:

startButtonPosition = new Vector2((graphics.GraphicsDevice.Viewport.Width - startButton.Width) / 2, 150); 

When I run this, I get the NullReferenceException error on the startButtonPosition initialisation saying that the object reference was not set to an instance of an object. Yet it is.

Answer 1

Either graphics or startButton , or one of their properties you are using, is set to null.

You can check this by hovering over the variables when an exception is thrown (Click break )

Remember just because you declare startButton as a variable, does not mean it is set to a value. You need to initialize it. (Ex: startButton = Content.Load<Texture2D... )

Answer 2

The code you provided is trying to initialize 'startButtonPosition' using 'startButton'. The problem is, you never initialize 'startButton' therefore it is 'null'.

@Pierre-Luc Pineault is right to suggest What is a NullReferenceException and how do I fix it?

Here's a link to initialize 'startButton'. Texture2D Constructor

I haven't used Texture2D but I'm assuming it'll look something like this:

Texture2D startButton = new Texture2D(graphics.GraphicsDevice, width, height);