Monitoring content loading — MRTK2

Scene operation progress

When content is being loaded or unloaded, the SceneOperationInProgress property will return true. You can monitor the progress of this operation via the SceneOperationProgress property.

The SceneOperationProgress value is the average of all current async scene operations. At the start of a content load, SceneOperationProgress will be zero. Once fully completed, SceneOperationProgress will be set to 1 and will remain at 1 until the next operation takes place. Note that only content scene operations affect these properties.

These properties reflect the state of an entire operation from start to finish, even if that operation includes multiple steps:

IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();

// First do an additive scene load
// SceneOperationInProgress will be true for the duration of this operation
// SceneOperationProgress will show 0-1 as it completes
await sceneSystem.LoadContent("ContentScene1");

// Now do a single scene load
// This will result in two actions back-to-back
// First "ContentScene1" will be unloaded
// Then "ContentScene2" will be loaded
// SceneOperationInProgress will be true for the duration of this operation
// SceneOperationProgress will show 0-1 as it completes
sceneSystem.LoadContent("ContentScene2", LoadSceneMode.Single)

Progress examples

SceneOperationInProgress can be useful if activity should be suspended while content is being loaded:

public class FooManager : MonoBehaviour
{
    private void Update()
    {
        IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();

        // Don't update foos while a scene operation is in progress
        if (sceneSystem.SceneOperationInProgress)
        {
            return;
        }

        // Update foos
        ...
    }
    ...
}

SceneOperationProgress can be used to display progress dialogs:

public class ProgressDialog : MonoBehaviour
{
    private void Update()
    {
        IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();

        if (sceneSystem.SceneOperationInProgress)
        {
            DisplayProgressIndicator(sceneSystem.SceneOperationProgress);
        }
        else
        {
            HideProgressIndicator();
        }
    }
    ...
}

---

Monitoring with actions

The Scene System provides several actions to let you know when scenes are being loaded or unloaded. Each action relays the name of the affected scene.

If a load or unload operation involves multiple scenes, the relevant actions will be invoked once per affected scene. They are also invoked all at once when the load or unload operation is fully completed. For this reason it's recommended that you use OnWillUnload actions to detect content that will be destroyed, as opposed to using OnUnloaded actions to detect destroyed content after the fact.

On the flip side, because OnLoaded actions are only invoked when all scenes are activated and fully loaded, using OnLoaded actions to detect and use new content is guaranteed to be safe.

Action	When it's invoked	Content Scenes	Lighting Scenes	Manager Scenes
OnWillLoadContent	Just prior to a content scene load	•
OnContentLoaded	After all content scenes in a load operation have been fully loaded and activated	•
OnWillUnloadContent	Just prior to a content scene unload operation	•
OnContentUnloaded	After all content scenes in an unload operation have been fully unloaded	•
OnWillLoadLighting	Just prior to a lighting scene load		•
OnLightingLoaded	After a lighting scene has been fully loaded and activated		•
OnWillUnloadLighting	Just prior to a lighting scene unload		•
OnLightingUnloaded	After a lighting scene has been fully unloaded		•
OnWillLoadScene	Just prior to a scene load	•	•	•
OnSceneLoaded	After all scenes in an operation are fully loaded and activated	•	•	•
OnWillUnloadScene	Just prior to a scene unload	•	•	•
OnSceneUnloaded	After a scene is fully unloaded	•	•	•

Action examples

Another progress dialog example using actions and a coroutine instead of Update:

public class ProgressDialog : MonoBehaviour
{
    private bool displayingProgress = false;

    private void Start()
    {
        IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();
        sceneSystem.OnWillLoadContent += HandleSceneOperation;
        sceneSystem.OnWillUnloadContent += HandleSceneOperation;
    }

    private void HandleSceneOperation (string sceneName)
    {
        // This may be invoked multiple times per frame - once per scene being loaded or unloaded.
        // So filter the events appropriately.
        if (displayingProgress)
        {
            return;
        }

        displayingProgress = true;
        StartCoroutine(DisplayProgress());
    }

    private IEnumerator DisplayProgress()
    {
        IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();

        while (sceneSystem.SceneOperationInProgress)
        {
            DisplayProgressIndicator(sceneSystem.SceneOperationProgress);
            yield return null;
        }

        HideProgressIndicator();
        displayingProgress = false;
    }

    ...
}

---

Controlling scene activation

By default content scenes are set to activate when loaded. If you want to control scene activation manually, you can pass a SceneActivationToken to any content load method. If multiple content scenes are being loaded by a single operation, this activation token will apply to all scenes.

IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();

SceneActivationToken activationToken = new SceneActivationToken();

// Load the content and pass the activation token
sceneSystem.LoadContent(new string[] { "ContentScene1", "ContentScene2", "ContentScene3" }, LoadSceneMode.Additive, activationToken);

// Wait until all users have joined the experience
while (!AllUsersHaveJoinedExperience())
{
    await Task.Yield();
}

// Let scene system know we're ready to activate all scenes
activationToken.AllowSceneActivation = true;

// Wait for all scenes to be fully loaded and activated
while (sceneSystem.SceneOperationInProgress)
{
    await Task.Yield();
}

// Proceed with experience

---

Checking which content is loaded

The ContentSceneNames property provides an array of available content scenes in order of build index. You can check whether these scenes are loaded via IsContentLoaded(string contentName).

IMixedRealitySceneSystem sceneSystem = MixedRealityToolkit.Instance.GetService<IMixedRealitySceneSystem>();

string[] contentSceneNames = sceneSystem.ContentSceneNames;
bool[] loadStatus = new bool[contentSceneNames.Length];

for (int i = 0; i < contentSceneNames.Length; i++>)
{
    loadStatus[i] = sceneSystem.IsContentLoaded(contentSceneNames[i]);
}