对象引用未设置为对象的实例（C＃）

Question

I can't seem to get this working, I'm getting an error once opening my c# project file (.exe) and it says "object reference not set to an instance of an object". Here's the line and the one below it.

// Update the actual position

Actor.Position = new Vector3(
                        Actor.PositionToSet.X, 
                        Actor.PositionToSet.Y, 
                        (Math.Round(
                            GetUserStepHeight(
                                Actor.PositionToSet),
                                1)));

Actor.PositionToSet = null;

Answer 1

The possibility is, either 1. Actor is null or 2. Actor.PositionToSet is null .

To check, either have this:

if(Actor == null){
    System.Console.WriteLine("Actor is NULL");
}

if(Actor.PositionToSet == null){
    System.Console.WriteLine("Actor.PositionToSet is NULL");
}

or use the LINE BY LINE debugger in Visual Studio.

Here is a piece of advice I got years ago:

1. Think before you code, and build a mental model of the code, then when things break, just reflect on what went wrong without looking at the code.

2. Unit test your code, make it a standard practice of your coding methodology. This will save you years of debugging time.

Answer 2

Please check that Actor or Actor.PositionToSet is not null. That is the only reason.