So... we have had a couple new releases since september. Any news on a non-2017.3.X version fix? Anyone working with unity ui can not upgrade AT ALL since 2017.1.1p1 (last version without the bug).

"Fixed in 2017.3.0b3" doesn't help us at all.

This is also happening in Unity 2017.30b1 on Linux.

Is there a fix for this? I updated to Unity 2017.3b9 and this issue is back!

(Removing foot from mouth) I just tried using 2017.1.2p2, and at least in the Editor it seems fixed for me.

sigh... one of the (few) reasons I wish I'd stayed with open-source Cocos2d-x; if a bug was found, even if the official build wouldn't include it for a while, I could always fix the code directly in my project.

Oh, Unity just stop it!!! So tired of stupid bugs that cost me a weekend!
It happens to me when onClick has a callback with bool paramenter.

Yeah I am curious too. Its interesting that the priority is 2 (must be fixed in next final release). But they haven't done so in 2017.1.1f and even not now in 2017.2... I mean 2017.3 seems to be months ahead - they need to backport it ??

Will this fix be backported to 2017.1 or 2017.2 ?

Hi all who are watching - just thought people suffering from this bug might want to be aware that there's a [dirty] workaround you can apply. The issue in question is that the implementing generically parameterised UnityEvent Invoke methods have a bug in how they iterate their invokable calls (you can see it in the disassembly). A simple way to work around this is to forceably invoke the Invoke method on UnityEventBase passing through the array of args correctly using reflection.

What we did is create an extension method for UnityEvent (but in your case you may need to create equivalents for, for instance UnityEvent<T0, T1> etc...) which does just that (see below). We then subclassed Button, and wholesale replaced all references to Unity UI buttons to ours, by just find/replacing the relevant script reference in all prefab/scene files. How our button's OnClick is shown below.

Note that as the bug is in the UnityEvent types this may or may not be a workable solution for you, and will manifest for all types which make use of UnityEvent (for instance Toggles) - we just only had buttons that we needed to solve.

Extension method:
private static object[] s_unityEventEmptyObjectArray = new object[1]{new object[0]};
private static MethodInfo s_unityEventInvokeMethod = null;

public static void SafeInvoke(this UnityEvent unityEvent)
{
if (s_unityEventInvokeMethod == null)
{
s_unityEventInvokeMethod = unityEvent.GetType().BaseType.GetMethod("Invoke",
BindingFlags.NonPublic | BindingFlags.Instance,
null,
new System.Type[]{typeof(UnityEngine.Object[])},
null);
}

s_unityEventInvokeMethod.Invoke(unityEvent, s_unityEventEmptyObjectArray);
}

Button OnClick method:
public override void OnPointerClick(UnityEngine.EventSystems.PointerEventData eventData)
{
// Don't call base class as onClick.Invoke() calls each thing multiple times

// Early outs...
if (!IsActive () || !IsInteractable ())
{
return;
}

if (eventData.button != UnityEngine.EventSystems.PointerEventData.InputButton.Left)
{
return;
}

// Use our magic method.
onClick.SafeInvoke();
}

Worth mentioning, it is not just onclick.
I created a simple ExecuteEvent script, which is called by the button.
My hope was to migrate the event to this script and call it from the button. No luck.

So, the "Workaround is possible" is true, but it is a much messier solution than what I initially imagined.