How to change a button in Unity 5?

Hello, I have a button script to change a button but it won't work. I have debugged and tried everything but none will work. Here is the code:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using UnityEngine.UI;
4. using System;
5. using UnityEngine.Events;
6. using UnityEngine.Sprites;
7.  
8. public class ChangeScene : MonoBehaviour {
9.     Text txt;
10.     // Use this for initialization
11.     void Start () {
12.         txt = gameObject.GetComponent<Text>();
13.     }
14.     IEnumerator wait (int time) {
15.         yield return new WaitForSeconds(time);
16.         Debug.Log("wait");
17.     }
18.     public void changeText(int pass){
19.         Debug.Log("start");
20.         if(pass == 1){
21.             txt.text = "Test in progress...";
22.             Debug.Log("work1");
23.             wait(5);
24.             Debug.Log("work2");
25.             txt.text = "";
26.         }
27.         else {
28.             txt.text = "Error, please report to Sarmad Wahab. Code: KB56";
29.             Debug.Log("Work");
30.             wait(4);
31.             txt.text = "";
32.         }
33.     }

It gives me the "start" but not "work" or "wait";
and when I click the button it gives me that ^ and this :

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. ChangeScene.changeText (Int32 pass) (at Assets/ChangeScene.cs:21)
3. UnityEngine.Events.InvokableCall`1[System.Int32].Invoke (System.Object[] args) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:141)
4. UnityEngine.Events.CachedInvokableCall`1[System.Int32].Invoke (System.Object[] args) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:259)
5. UnityEngine.Events.InvokableCallList.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:574)
6. UnityEngine.Events.UnityEventBase.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:716)
7. UnityEngine.Events.UnityEvent

Thanks for the help;
and I may reply with a semicolon at the end of a sentence; (thats just my addiction to semicolons, lol)

 

Well, it seems to be getting stuck on line 21, saying the Object reference is not set to an instance of an object. So it seems like your txt variable is not actually getting a Text component in Start, I assume.

Do you have this script attached to something that actually has a Text component? If it's in a child, you'll have to use GetComponentInChildren<> and make sure there's only 1 text for it to find (or that it's the next in the heirarchy).

Also, you don't need to do gameObject.GetComponent. You can just use GetComponent<Text>.

 

For a Button you will want to do GetComponentInChildren() as the text GO is a child of the button control.

I believe @nesseggman is right that your txt reference is likely null.

If doing references like this, its always better to put some error trapping in to avoid issues like this, such as:

Code (CSharp):

1. txt = gameObject.GetComponent<Text>();
2. if(txt == null)
3.     Debug.LogError("txt reference not found");

 

I have it attached to a gameobject (empty) called _Manager, when the button is clicked, it tells _MAnager to launch the script with pass to be assigend to 1.

 

Then what is happening is that at Start, the script is searching for a Text object that is a component of _Manager itself. If it doesn't find one, GetComponent returns null, so txt == null. In line 21, you're trying to access the text of txt, but txt is null, which throws the error and stops the code from continuing into the "work1" debug line.

You probably want to attach this script to your button, or in some other way make sure that txt is being set to the Text component that you want. If all of these are preloaded things in the scene (_Manager, the Button, and its Text), you can make your variable txt public and just assign it in the inspector.