NullReferenceException on Unity 2019.4.1 about unitysimplefilebrowser

[artur-ag]

Not during the start of the scene, no, it gets created when I invoke the file browser by clicking on a UI button in my own Canvas. But when I was getting the error yesterday, I can't remember if the SimpleFileBrowserCanvas object was there from the beginning or not, and now I can't reproduce the exception.

I did two changes in the SimpleFileBrowserCanvas: I disabled the EventSystem, because I already have one in my scene, and changed the CanvasScaler reference resolution.

EDIT: I managed to reproduce the bug!! It happened while I started the game in the editor while having the SimpleFileBrowserCanvas prefab opened in Prefab mode. Here are the steps to reproduce it in Unity 2020.2.1f1:

1. Create an empty scene (I tried with my existing scene and with an empty one, and it happened both times).
2. Double-click SimpleFileBrowserCanvas.prefab in the Project panel. This will open it in Prefab mode, and makes the scene panel background blue.
3. With the prefab still open, press Play.
4. The following exception occurs right after starting:

NullReferenceException: Object reference not set to an instance of an object
SimpleFileBrowser.RecycledListView.UpdateList () (at Assets/Plugins/SimpleFileBrowser/Scripts/SimpleRecycledListView/RecycledListView.cs:55)
SimpleFileBrowser.FileBrowser.RefreshFiles (System.Boolean pathChanged) (at Assets/Plugins/SimpleFileBrowser/Scripts/FileBrowser.cs:1621)
SimpleFileBrowser.FileBrowser.OnShowHiddenFilesToggleChanged () (at Assets/Plugins/SimpleFileBrowser/Scripts/FileBrowser.cs:1266)
UnityEngine.Events.InvokableCall.Invoke () (at <e414e10bfe5f45729ff122f3359de21b>:0)
UnityEngine.Events.UnityEvent`1[T0].Invoke (T0 arg0) (at <e414e10bfe5f45729ff122f3359de21b>:0)
UnityEngine.UI.Toggle.Rebuild (UnityEngine.UI.CanvasUpdate executing) (at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Toggle.cs:130)
UnityEngine.UI.CanvasUpdateRegistry.PerformUpdate () (at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/CanvasUpdateRegistry.cs:182)
UnityEngine.UI.ScrollRect:LateUpdate() (at C:/Program Files/Unity/Hub/Editor/2020.2.1f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/ScrollRect.cs:808)

I must've had the prefab mode open yesterday and didn't realize it.

[yasirkula]

The closest setup I have is Unity 2019.4.0f1 on Windows and I can't reproduce this issue with these reproduction steps. And frankly, it should be impossible to encounter this Issue. Let's see why:

• Error comes from this line:

  UnitySimpleFileBrowser/Plugins/SimpleFileBrowser/Scripts/SimpleRecycledListView/RecycledListView.cs

  Line 55 in 52ecce6

  float newHeight = Mathf.Max( 1f, adapter.Count * itemHeight );

• Value of adapter is assigned here:

  UnitySimpleFileBrowser/Plugins/SimpleFileBrowser/Scripts/SimpleRecycledListView/RecycledListView.cs

  Lines 44 to 50 in 52ecce6

  	public void SetAdapter( IListViewAdapter adapter )
  	{
  	this.adapter = adapter;
  	itemHeight = adapter.ItemHeight;
  	_1OverItemHeight = 1f / itemHeight;
  	}

• This function is called here

  UnitySimpleFileBrowser/Plugins/SimpleFileBrowser/Scripts/FileBrowser.cs

  Line 584 in 52ecce6

  listView.SetAdapter( this );

which is inside here:

UnitySimpleFileBrowser/Plugins/SimpleFileBrowser/Scripts/FileBrowser.cs

Line 536 in 52ecce6

private void Awake()

Awake is called before any other functions. If there was an exception that interrupted Awake, this error would be possible but you didn't mention any in the Issue description.

Are there any other steps that you didn't mention in Reproduction steps? You should create a new Unity project, import the plugin there and take note of every step you take until you can reproduce this issue and report all of these steps in Reproduction steps.

[artur-ag]

I'm finding the same error with version 1.4.1, running in Unity 2020.2.1f1 on Windows 10.
It happens one single time, when the scene starts, even before I invoke the file browser. But after that, everything works as expected: I can open the browser, select a file, etc.

@yasirkula from what you say, it makes sense that it happens, because during the start of my scene, I don't invoke any file browser, so the Awake method doesn't have a chance to run. But somehow Unity itself is invoking something that runs SimpleFileBrowser.FileBrowser.OnShowHiddenFilesToggleChanged.

I already have an EventSystem in my scene, so I disabled the EventSystem gameobject inside SimpleFileBrowserCanvas. I didn't try it in an empty scene without an existing EventSystem... could that be it? The already-existing EventSystem is triggering the toggle changed event?

[artur-ag]

I restarted Unity and now I can't reproduce the bug anymore... I'm not sure what fixed it, because I didn't change anything in my setup. Maybe it was because I imported a new version of Runtime File Browser without deleting all the files from the previous one.

[yasirkula]

I don't think it is related to EventSystem. Do you have an instance of SimpleFileBrowserCanvas object in your scene? If so, is it active? Did you modify it in any way?

[yasirkula]

Awesome! I was able to reproduce the error on 2018.4, too.