gistfile1.md

Hi,

We have a feature that if you do:

m_MyGUiLayer = GetComponent<GUILayer>();

if it turns out there was no GUILayer component, if you later use m_MyGUILayer, instead of getting a NullReferenceException (what you might expect as a c# dev), you get:

MissingComponentException: There is no 'GUILayer' attached to the "Directional Light" game object, but a script is trying to access it.
You probably need to add a GUILayer to the game object "Directional Light". Or your script needs to check if the component is attached before using it.
NewBehaviourScript.Start () (at Assets/NewBehaviourScript.cs:10)

We are able to give a much better error message that contains the type of the component that was requested, the gameobject name of the gameobject that apparently didn't have the component, and it also has "context" of that gameobject, so if you click this message in the console window, the editor will actually "ping" the gameobject in question. We do this only in the editor.

Awesome.

This feature comes at a (editor-only) cost of a c# allocation for that error message string (as well as the fake-null-object that holds the string). Every week, we get a bugreport about "GetComponent() is allocating, this is madness!" from folks that (probably) don't realise that this allocation only happens in the editor.

We're debating wether or not this error message provides enough value compared to cost it brings. (costs: apparently users getting confused about it a lot, us having to deal with a flow of bugreports about it, editor-allocation patterns being different from the player).

Options on the table are:

• Drop the feature, and make GetCompoment() return a normal null instead.
• add GetComponent(bool niceErrorMessageWhenNotFound = true), so that if you care about not having the allocation in the editor, you can tell us to not mak eit.
• not do anything about it.
• fake it, and internally mark this allocation as editor-only, and then have the profiler actually hide the allocation.

I'd love to hear from users if they have ever found the MissingComponentException to be especially helpful, and in which scenarios that was, and how one's workflow would be negatively affected by no longer having this detailed exception.

Thanks, Lucas (you can reply here, or on twitter @lucasmeijer)

Hi,

From a point of view where many users are not experts, I would make it as an option so that middleware publishers can provide a good feedback and keep themselves out of the loop on such problem, else we always get users getting back to the Author to complain on something that is really a scene setup issue.

It's always good to have information, why rely on expertize and painful debugging sessions when the log can lift any guess work on the issue. The fact that is behaves differently in Editor and at Runtime is another part of the problem, and I don't see this as a reason to remove this feature all together.

Thanks for your hardwork :)

Bye,

Jean

I would drop it if I could chose. I have been using unity enough time and its pretty self explanatory when this happens.

I'd say remove it.

I think the intention is primarily to help new developers make sense of what's gone wrong with their scripts, but my feeling is that this is hand-holding them too excessively. For the sake of consistency I'd rather teach a beginner about how to handle a NRE than how to handle both this special exception and a NRE.

Moreover, the wording of the exception seems unhelpful or misleading. That is, if I as a neophyte Unity user see that message in the console, how am I to take it? The "You probably need to add a..." portion seems clear enough that it might be a compelling option for a beginner to pursue, but there's no way of knowing without understanding the context of the exception whether that is the right course of action. In other words, I feel like the message might encourage "try this fix without understanding the problem" behaviour.

I would remove it.

If you want to help new developers, then it should be better to append a link/button to the error message (row) in the Console (maybe at the right of each row when the row is selected) with the text: "Know more about this error" / "How to fix this?" / "Why this error?" or something similar for the most common exceptions/errors/warnings. And when you click on it, you get redirected to the Unity manual page with this error/warning explanation, when it happens, how to avoid it, etc. (Doing this, the change is only related to the Unity Editor, and at the same time this option deliver much more information, since you can add as much errors/warnings explanation in the docs, as you need.)

You could add a toggle button to the Console and have this enabled by default.

I think the best approach would be to keep the error message, internally mark the allocation as editor-only, and then instead of hiding it in the profiler have a clearly labeled editor only section in the profiler that is user hide-able. That way you can have nice error messages and be transparent about what the editor is doing, but also keep a clear separation that shows what will/will not happen in a built player.

I think you should do nothing about this, not because I care about the editor message, but because there is no reason to spend time changing.

As someone who uses Unity on mobile and cares about individual bytes, with 15 years of experience doing this sort of profiling on C++, this issue has never yet hit my own radar. GetComponent() is allocating? Who cares. Now, I wonder if the assetbundle resource I loaded then expected to get dropped during a Resources.UnloadUnusedAssets actually DID get unloaded.

You're spending valuable dev resource on making people who profile code-side byte allocations the editor happier.

There are two big cases to use GetComponent call:

1. During initialization, to obtain references to components you KNOW are there.
2. During gameplay, to check if a gameobject is of a certain kind (i.e. has a component you need)

In first case, you obviously don't expect to get null at all. In fact, if you get a null, the error has already happened, and exception should be thrown right away.
In second case, getting null reference is actually an expected outcome. If this null value gets used later, it's an error, but the problem is NOT "missing component", but you forgetting to check.

The correct way to handle this would be to add some method (GetRequiredComponent?) that throws right away if component is not found, and have GetComponent return plain nulls. Adding a "special kind of null" is helpful neither to experienced programmers (who dont expect this and get confused), nor to newbies (who now have to learn about a special-case and confusing behaviour - nothing works this way outside of unity)

I don't see the point in the GetComponent variant of this exception. However is this the same exception thrown if a reference is serialised, but the target then goes missing? That one is very handy indeed and I would hate to see it go.

Compared to the GetComponent call, that scenario clearly highlights a specific bug of unexpected state.

There is a yet another issue with this. I've personally wasted half a day trying to track it out down.

Renderer someRenderer = GetComponent<Renderer> ?? someOtherObject.GetComponent<Renderer>

obviously, this resulted in different results between editor and player, as null coalescence operator ignores operator overload and actually returns the fake-error-string-containing-object instead of branching to the right side.