Instance of an object in C#

Question

I am encountering a bug in a game I am trying to make. I am getting the following error.

NullReferenceException: Object reference not set to an instance of an object

This same code works fine in one of my other scripts but in this one it continues to through this error. I thought I set it to an instance of the object but I guess not.

UnityEngine.Component book001GUIOld = GameObject.FindWithTag("Book001Canvas").GetComponent("Canvas");
UnityEngine.Behaviour book001GUI = (UnityEngine.Behaviour)book001GUIOld;

Any Suggestions? Let me know if you need more of the code. I have also tried.

UnityEngine.Behaviour book001GUI = GameObject.FindWithTag("Book001Canvas").GetComponent("Canvas") as behaviour;

just find out the bottom most stack which the object is null but it shouldnt be...NullReference is one of the easiest bug to debug.. — Steve, Jan 24 '15 at 00:35

score 0 · Answer 1 · edited Jan 24 '15 at 00:43

0

Must be because GameObject.FindWithTag("Book001Canvas") returned null, then .GetComponent("Canvas"); throws a exception.

edited Jan 24 '15 at 00:43

Rufus L

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answered Jan 24 '15 at 00:36

Ecnerwal

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GameObject seems to be a static class and .FindWithTag a static method. no? – Ecnerwal Jan 24 '15 at 00:44
Ah, I think you're right. – Rufus L Jan 24 '15 at 00:48

score 0 · Accepted Answer · answered Jan 24 '15 at 00:54

From the GameObject.FindWithTag documentation:

Description

Returns one active GameObject tagged tag. Returns null if no GameObject was found.

So you might want to try to catch the error:

var book001Canvas = GameObject.FindWithTag("Book001Canvas");

if (book001Canvass != null)
{
    UnityEngine.Component book001GUIOld = book001Canvas.GetComponent("Canvas");
}
else
{
    // Recover from not finding an object with the Book001Canvas tag
}

Instance of an object in C#

2 Answers2