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By Design
Votes
1
Found in [Package]
1.7.8
Issue ID
UVSB-2379
Regression
No
ArgumentNullException when trying to check if EventHook == null
How to reproduce:
1. Open the user's attached project
2. Enter Play mode
3. Observe the Console
Expected result: There are no errors in the Console
Actual result: Console produces the "ArgumentNullException: Value cannot be null." error
Reproducible with: 1.7.8 (2021.3.4f1, 2022.1.5f1, 2022.2.0a16)
Couldn't test with: 2019.4.39f1, 2020.3.36f1 (No Visual Scripting version available)
Reproducible on: Windows 10
Note: Script that causes the error can be found in Assets/Scripts
-
jeanedouard_unity
Aug 24, 2022 17:46
The user uses the following code that breaks :
EventHook m_eventHook;
void Start()
{
m_eventHook = new EventHook("DoWork");
EventBus.Register<int>(m_eventHook, DoWork);
}private void Update()
{
if (m_eventHook != null)
{
EventBus.Trigger(m_eventHook, 1);
}
}
But EvenHook is a struct and structs are value types. This means it cannot be null and when checking if the eventHook is null it falls back on a default implicit operator which is by design. If users want to check if the EventHook is null they must use the Nullable Value Types C#8 feature. Here is how the code should look like:EventHook? m_eventHook;
void Start()
{
m_eventHook = new EventHook("DoWork");
EventBus.Register<int>(m_eventHook.Value, DoWork);
}private void Update()
{
if (m_eventHook != null)
{
EventBus.Trigger(m_eventHook.Value, 1);
}
} -
SmartMediaNL
Jun 10, 2022 10:57
What happens is that the check to see if the EventHook is null will in turn (internally by Unity Engine) do its own even hook call with a string that is null resulting in the error thrown mentioned above.
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Resolution Note:
The issue is in the user's project (see details in comments)