Unity UI dynamic Buttons

Question

Hello Forum,

I'm trying to make a menu that is built at runtime.

         for (int i = 0; i < bd.ItemCount(); i++) {
 
             buttons.Add((GameObject)Instantiate(button));
             buttons[i].transform.SetParent(transform, false);
             buttons[i].transform.GetChild(0).GetComponent<Text>().text = bd.GetNameById((byte)i);
 
             Vector3 position = buttons[i].GetComponent<RectTransform>().position;
             position.y -= 40 * i;
             buttons[i].GetComponent<RectTransform>().position = position;
 
             buttons[i].GetComponent<Button>().onClick.AddListener(() => {
                 builder.SelectItem(buttons[i].transform.GetChild(0).GetComponent<Text>().text);
             });
         }

You can ignore the first part. I can imagine why this isn't working but I have no better idea. The problem is that the call to the method is when the i does not exist anymore. How can I know which button called the method?

Thanks!

Answer 1

Best Answer

Answer by Mmmpies · Jan 13, 2015 at 06:06 PM

Try creating them like this, there's an issue with the way C# hold references to variables but I can get the buttons to Debug.Log the button number when I create them like this and set the Lambda using temp variables. I believe the issue is fixed in 5 but not used 5 yet so can't be 100% sure:

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class LambdaButtons : MonoBehaviour {
 
     public GameObject prefabButton;
     public RectTransform ParentPanel;
 
     // Use this for initialization
     void Start () {
 
         for(int i = 0; i < 5; i++)
         {
             GameObject goButton = (GameObject)Instantiate(prefabButton);
             goButton.transform.SetParent(ParentPanel, false);
             goButton.transform.localScale = new Vector3(1, 1, 1);
 
             Button tempButton = goButton.GetComponent<Button>();
             int tempInt = i;
 
             tempButton.onClick.AddListener(() => ButtonClicked(tempInt));
         }
 
     
     }
 
     void ButtonClicked(int buttonNo)
     {
         Debug.Log ("Button clicked = " + buttonNo);
     }
 
 }

Also sorry it took so long, I saw this at lunch time but was at work for the afternoon. You'll need a vertical layout group on the panel you put them in so they don't build on top of each other. I did that and put a layout element on the button prefab with a minimum height of 30, I also stopped the expand on height in the panels vertical group. This is the result I get:

LambdaButtons

lambdabuttons.png (32.0 kB)

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stulleman · Jan 15, 2015 at 01:03 PM 0

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Thank you very much! Hope they fix this, as this seems not very intuitive to me. Anyway thanks for your help, better late then never :P

Icarus619 · Apr 12, 2016 at 05:31 PM 0

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Hi, somehow all five buttons are rendered above each other and not on the panel. What am i doing wrong here? I assigned a Panel in the upper left corner with a decent size, but all buttons are rendered somewhere on the screen..

Laaevin · Jul 13, 2017 at 09:39 PM 0

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Sorry to necro this. I'm trying to accomplish this same task only in Javascript and I'm getting stuck where your code is on line 22. When I try to call a function with this line of code:

tempButton[tempInt].GetComponentInChildren.().onClick.AddListener(ButtonClicked(tempInt));

It says: "No appropriate version of UnityEngine.Events.UnityEvent.AddListener' for the argument list '(void)' was found."

Can anyone help me figure out how to have each button call a function with a different input?

gobyfazakas · Jul 13, 2020 at 09:02 AM 0

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Thanks a lot, if you ever read this you helped me, and many others who didn't bother commenting

Answer 2

Answer by WarpZone · Jan 16, 2017 at 03:29 PM

@Icarus619 Like he said in his answer, you'll need a vertical layout group on the panel you put them in so they don't build on top of each other.

Here's a youtube video that will walk you through adding a vertical layout group to your items: https://www.youtube.com/watch?v=lUun2xW6FJ4

It also tells you how to implement a scrollbar, in case your list gets taller than the screen.

Good luck.

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Unity UI dynamic Buttons

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