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*.transform.SetParent(transform, false);*

_ buttons*.transform.GetChild(0).GetComponent().text = bd.GetNameById((byte)i);*_

_ Vector3 position = buttons*.GetComponent().position;
position.y -= 40 * i;
buttons.GetComponent().position = position;*_

_ buttons*.GetComponent().onClick.AddListener(() => {
builder.SelectItem(buttons.transform.GetChild(0).GetComponent().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!_

Scrooge

The bug is not fixed yet. (January 2016, version 5.3).

– Schreiber

Hi All I have also looking for the code. First time i have run the code. It works perfect. But after that i have try to run the above code. It shows the error... NullReferenceException: Object reference not set to an instance of an object It does not works.. How can i solve it......

– Deprecative

Answer 1

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:

38731-lambdabuttons.png423×620 31.2 KB

Orotund

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

– Scrooge

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..

– Alpers

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?

– Krakow

Answer 2

@Alpers 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: ** Unity UI Tutorial - How to make a scrollable list - YouTube **

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

Good luck.

Kania