Unity3D invalid token error on official code from documentation

December 14, 2021

i was trying to set up simple ad system in my game in unity but the rewarded ads script from unity documentation is giving me invalid token error and i have no idea why

using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Advertisements;

public class RewardedAdsButton : MonoBehaviour, IUnityAdsLoadListener, IUnityAdsShowListener
{
    [SerializeField] Button _showAdButton;
    [SerializeField] string _androidAdUnitId = "Rewarded_Android";
    [SerializeField] string _iOSAdUnitId = "Rewarded_iOS";
    public string _adUnitId = null;
#if UNITY_IOS
        _adUnitId = _iOSAdUnitId;
#elif UNITY_ANDROID
        _adUnitId = _androidAdUnitId;
#endif

Assets\Scripts\RewardedAdsButton.cs(14,13): error CS1519: Invalid token ‘=’ in class, struct, or interface member declaration
Assets\Scripts\RewardedAdsButton.cs(14,31): error CS1519: Invalid token ‘;’ in class, struct, or interface member declaration

>Solution :

I doubt this is shown as that in any official code. you can’t just reassign a field on class level. You can’t have this outside of any method or have to do it on the entire field declaration.

This is probably supposed to happen in method like e.g. in Awake

public class RewardedAdsButton : MonoBehaviour, IUnityAdsLoadListener, IUnityAdsShowListener
{
    [SerializeField] Button _showAdButton;
    [SerializeField] string _androidAdUnitId = "Rewarded_Android";
    [SerializeField] string _iOSAdUnitId = "Rewarded_iOS";

    [NonSerialized] public string _adUnitId = null;

    private void Awake ()
    {
#if UNITY_IOS
        _adUnitId = _iOSAdUnitId;
#elif UNITY_ANDROID
        _adUnitId = _androidAdUnitId;
#endif
    }

    ...
}

Or alternatively I would simply use a property like e.g.

public class RewardedAdsButton : MonoBehaviour, IUnityAdsLoadListener, IUnityAdsShowListener
{
    [SerializeField] Button _showAdButton;
    [SerializeField] string _androidAdUnitId = "Rewarded_Android";
    [SerializeField] string _iOSAdUnitId = "Rewarded_iOS";

    public string _adUnitId
    {
        get
        {
#if UNITY_IOS
            return _iOSAdUnitId;
#elif UNITY_ANDROID
            return _androidAdUnitId;
#else
            return null;
#endif
        }
    }