Faking mouse click behavior in OnGUI via Event.current

Unity Engine
,
1

I’m writing an EditorGUI field for my custom serialized field, so I’m trying to mimic that API.

Here’s an example of what I’m trying to do:

public static Rect MyField(Rect position)
{
    var evt = Event.current;
    if (evt.type == EventType.MouseDown)
        Debug.Log("MyField clicked!");
}

I’m trying to test it, with a TestEditorWindow and onGui callbacks:

public class TestEditorWindow : EditorWindow
{
    public Action onGui;

    void OnGUI() => onGui?.Invoke();
}

[UnityTest]
public IEnumerator TestMyField()
{
    bool onGuiCalled = false;
    var position = new Rect(x: 0, y: 0, width: 150, height: 30);
    void OnGUI()
    {
        var evt = new Event() { type = EventType.MouseDown, clickCount = 1, mousePosition = position.center };
        Event.current = evt;
        MyField(position);
        onGuiCalled = true;
    }
    var testWindow = EditorWindow.GetWindow<TestEditorWindow>();
    testWindow.onGui = OnGUI;
    yield return new WaitUntil(() => onGuiCalled);
    // Assert for MyField behavior here...
}

The issue I run into is that the EventType is changed to EventType.Ignored. I realize this is probably pretty poor testing behavior because the Layout and Repaint current events are overwritten.

I was thinking there was some behavior in Event.current that was validating the set event, so I tried changing my custom field to look like

public static Rect MyField(Rect position, Event customEvent = null)
{
    var evt = customEvent ?? Event.current;
    if (evt.type == EventType.MouseDown)
        Debug.Log("MyField clicked!");
}

And I changed the OnGUI method in my test to look like:

void OnGUI()
{
    var evt = new Event() { type = EventType.MouseDown, clickCount = 1, mousePosition = position.center };
    MyField(position, evt);
    onGuiCalled = true;
}

But somehow, the event type is still changed to EventType.Ignored. I tried debugging the creation of the event, and the event type is changed when it’s passed to MyField. I have no clue how this is happening.

After this, I was thinking that I probably shouldn’t be trying to set the current event while the OnGUI method is being called. I reverted the changes I made earlier, and tried the following:

[UnityTest]
public IEnumerator TestMyField()
{
    bool onGuiCalled = false;
    var position = new Rect(x: 0, y: 0, width: 150, height: 30);
    void OnGUI()
    {
        Event.current = evt;
        MyField(position);
        onGuiCalled = true;
    }
    var testWindow = EditorWindow.GetWindow<TestEditorWindow>();
    testWindow.onGui = OnGUI;
    var evt = new Event() { type = EventType.MouseDown, clickCount = 1, mousePosition = position.center };
    Event.current = evt;
    yield return new WaitUntil(() => onGuiCalled);
    // Assert for MyField behavior here...
}

However, the OnGUI method never received the set Event.current. No amount of yield return null and combinations of WaitUntil could get the OnGUI method to receive the event.

So I tried digging through the API one more time, and stumbled upon a method, EditorWindow.SendEvent. It looked promising–perhaps this was the way I could invoke an event in an editor window.

[UnityTest]
public IEnumerator TestMyField()
{
    bool onGuiCalled = false;
    var position = new Rect(x: 0, y: 0, width: 150, height: 30);
    void OnGUI()
    {
        Event.current = evt;
        MyField(position);
        onGuiCalled = true;
    }
    var testWindow = EditorWindow.GetWindow<TestEditorWindow>();
    testWindow.onGui = OnGUI;
    var evt = new Event() { type = EventType.MouseDown, clickCount = 1, mousePosition = position.center };
    testWindow.SendEvent(evt);
    yield return new WaitUntil(() => onGuiCalled);
    // Assert for MyField behavior here...
}

Nope! Somehow, EditorWindow.SendEvent automatically sets the EventType to EventType.Used.

I’ve been bashing my head at this problem for a couple hours now, and I need some help.

  • How the heck am I supposed to mock a simple MouseDownEvent at a position in IMGUI?
  • What’s causing my mouse down events set to Event.current to become ignored?
  • What magical being is causing the mouse down events passed to MyField to become ignored when they’re of type MouseDown after creation, and I don’t touch them in my editor script?

Sincerely, a Unity Dev with hopes of 100% Code Coverage.

2

To anyone wondering how I did it, I ended up doing the following:

Created my own GUIEvent valuetype:

public struct GUIEvent
{
    public EventType Type { get; }
 
    public GUIEvent(EventType type)
    {
        Type = type;
    }
}

Added an overload MyField method:

public static Rect MyField(Rect position)
{
    var evt = Event.current;
    return MyField(position, new GUIEvent(evt.type));
}

public static Rect MyField(Rect position, GUIEvent guiEvent)
{
    if (guiEvent.Type == EventType.MouseDown)
        Debug.Log("MyField clicked!");
    return position;
}

This gives me full control over the events I pass in. I still used the TestClass, but instead of calling MyField(Rect position), I called the overload MyField(Rect position, GUIEvent guiEvent). I have a separate test that tests the functionality of mapping Event.current to a GUIEvent. 100% Code Coverage is achievable!

I mean… code coverage has its faults, but it’s good to be able to know how to test all the things ;).