Add Listeners to array of Buttons

Question

Hi, using unity 5.6 -

I have three buttons that I am attempting to instantiate with listeners in C#. In my function TaskOnClick(), I want to be able to be able to tell w$$anonymous$$ch button has been clicked so I can add further functionality.

I am fairly sure I am mucking up some code in the Start() function and also not sure if I need to add a bool to the TaskOnClick() function or if I should just use IF or Switch statements to parse through the clicks. I have been following t$$anonymous$$s example: https://docs.unity3d.com/ScriptReference/UI.Button-onClick.html

Here is my code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class Button02 : MonoBehaviour {
 
     public Button[] buttons;
 
     private void Start()
     {
         for (int i = 0; i < buttons.Length; i++)
         {
             Button btns = buttons[i].GetComponent<Button>();
             btns.onClick.AddListener(TaskOnClick);
         }
 
     }
 
     public void TaskOnClick()
     {
         // how can I add a boolean here to check w$$anonymous$$ch button has been clicked?
         Debug.Log("you have clicked t$$anonymous$$s button");
     }
 }

I am wondering if somet$$anonymous$$ng along the lines of t$$anonymous$$s in TaskOnClick() might work: (obviously t$$anonymous$$s is very crude....) Thank you in advance.

 public void TaskOnClick() {
      for (int i= 0; i < Lenght; i++) {
           if (buttons[0] == true)
                 'do somet$$anonymous$$ng'....
          else if(buttons[1] == true)
                 'do somet$$anonymous$$ng else'

Answer 1

Best Answer

Answer by Hellium · Jul 10, 2017 at 01:10 PM

All the answers given previously won't work because of the closure problem.

W$$anonymous$$le the idea of using a specific delegate it the way to go, you have to "capture" the value of the loop index before assigning the delegate :

  for (int i = 0; i < buttons.Length; i++)
  {
        int closureIndex = i ; // Prevents the closure problem
        buttons[closureIndex].onClick.AddListener( () => TaskOnClick( closureIndex ) );
  }

  // ...
  public void TaskOnClick( int buttonIndex )
  {
      Debug.Log("You have clicked the button #" + buttonIndex, buttons[buttonIndex]);
  }

18 Show 4 · Share

CoryButler · Jul 10, 2017 at 01:41 PM 0

Share

I was unaware of the closure problem. The solution appears to do logically-speaking the same thing, but you are right. C# understands your code differently than mine. Thanks for the info.

brobes05 · Jul 10, 2017 at 09:51 PM 0

Share

@Hellium and @CoryButler -

I appreciate your responses. It has solved the issue of adding a listener. Thank you.

RealSoftGames · Nov 17, 2018 at 01:42 PM 0

Share

thank you i spent over 6 hours trying to figure out why my code wouldnt work. weirdly enough i have never heard of this closure problem, could you please explain why adding a new int param inside a for loop and assigning it the iterators value works. essentially using i in the for loop should do the exact same thing?

Hellium RealSoftGames · Nov 17, 2018 at 02:33 PM 0

Share

I may not be the best one to explain the problem, but I will try.

 for (int i = 0; i < buttons.Length; i++)
 {
      buttons[closureIndex].onClick.AddListener( () => TaskOnClick( i ) );
 }

With the previous code, you add a new listener to the onClick event. This listener in the following UnityAction : () => TaskOnClick( i ) . When one of the button is clicked, TaskOnClick is called, but it's not the value of i at the ith iteration which is used as the argument. It's a "reference" of i. Since there is 99,99% chance the for loop has ended beforehand, i contains the value buttons.Length.

By creating a new variable inside the loop, when TaskOnClick( closureIndex ) is called, the reference of the temporary variable is used as the parameter, and the problem disappears.

I hope it's clear enough for you.

Answer 2

Answer by CoryButler · Jul 10, 2017 at 12:36 PM

@brobes05

Use a delegate to pass the button's ID as an argument. Also, skip the btns variable.

 for (int i = 0; i < buttons.Length; i++)
 {
      buttons[i].GetComponent<Button>().onClick.AddListener(delegate{TaskOnClick(i);});
 }

Then, change the TaskOnClick() signature to TaskOnClick(int id).

1 · Share

Add Listeners to array of Buttons

2 Replies

Your answer

Welcome to Unity Answers

Follow this Question

Related Questions