Unclear NullReferenceException

Unity Engine
,
1

I have a NullReferenceException which i do not understand maybe it’s easy to explain.

The error is :

NullReferenceException: Object reference not set to an instance of an object
JsonStam.Start () (at Assets/JsonStam.cs:49)

I am assigning :
stam4.list[0].path = " blat";

I even made the constructor allocates the memory explicitly

[Serializable]
public class StamClass {
public Picture[ ] list;
public StamClass() {
list = new Picture[2];
}
}

[Serializable]
public class Picture {
public string path;
public string title;
}

What is the problem?
File Attached.

3126093–236794–JsonStam.cs (748 Bytes)

2

Your array has been allocated (list = new Picture[2]) but the elements in it have not. Since a class is a reference type you need to allocate each of them individually.

Or change Picture to be a struct instead of a class and it should work since structs are value types and don’t need to be allocated with new.

1 Like
3

I would put a constructor inside picture and put in the stamclass some values like

Picture b = new Picture(" text ", " text ");
or something like that

… so you would create an array of pictures and say

public Picture[ ] list;

…
list = new Picture[2];

and than for each picture in the aray you create a new object like the first line above…
I hope I don´t sound too complicated :slight_smile:

4

so here you go:

[Serializable]
public class StamClass {

public Picture[ ] list;

public StamClass() {

list = new Picture[2];
list [0] = new Picture (“”,“”);
}

public int Length() {

return(list.Length);

}

}

[Serializable]
public class Picture {

public string path;
public string title;

public Picture(string path2,string title2)
{
path = path2;
title = title2;
}

}

just change those two classes with my version above

5

My Problem was as Larku mentioned allocating the pointer doesnt allocate the class instance.
Thanks