ViewData persistence

Use the ViewData API to persist UI-specific state data after a domain reloads or when the Editor restarts. Persistent data is stored on each EditorWindow. Each VisualElement has a persistenceKey that must be set in order to enable ViewData persistence.

This topic provides examples on how to enable ViewData persistence for implemented controls and new objects.

Usage for implemented controls

If an element already supports persistence, set the persistenceKey to tell the system that it needs to save data. The persistenceKey must be unique compared against the keys for other visual elements.

Usage with VisualElement object inheritance

If you create a new VisualElement, you can have it support persistent data. The first step is to encapsulate your persistent data within one or more Serializable classes inside your element class:

[Serializable]
public class ExtraData
{
    public int m_Value = 0;
}
public ExtraData m_ExtraData;

The second step is to call the SavePersistentData() method whenever the persistent data changes. This ensures that the data is saved properly:

public int value
{
    get { return m_Value; }
    set
    {
        // do stuff
        SavePersistentData();
    }
}

The last step is to override OnPersistentDataReady():

// We do our real initial work here, once we know we can access our
// persistent data store.
protected override void OnPersistentDataReady()
{
    base.OnPersistentDataReady();

    // Optionally get a more unique key based on current parents.
    // This includes our own `persistenceKey`.
    var key = GetFullHierarchicalPersistenceKey();

    // Get or create a new ExtraData objects.
    m_ExtraData = GetOrCreatePersistentData<ExtraData>(m_ExtraData, key);
}

The example above also demonstrates how to generate and assign a unique key. Once the key is assigned, GetOrCreatePersistentData() returns the object with the persistence state, or as-is.

• 2018–11–02 Page amended with limited editorial review