UxmlAttributeConverter<T0>

Description

Converts a UxmlAttribute type to and from a string.

Fields marked with UxmlAttributeAttribute are represented in UXML by a single string attribute, however, to properly serialize these attributes, you must declare a UxmlAttributeConverter. This converter converts the string attribute value into the appropriate data type for the marked field.

Note: The following types have native support and you can use them without declaring a UxmlAttributeConverter:

• bool
• char
• string
• short
• int
• long
• uint
• ulong
• Enum
• float
• double
• Type(Additional resources: UxmlTypeReferenceAttribute)
• Color
• Hash128
• Length
• Bounds
• BoundsInt
• Rect
• RectInt
• Vector2
• Vector2Int
• Vector3
• Vector3Int
• Vector4
• Gradient
• AnimationCurve
• ToggleButtonGroupState

The following example creates a custom control that uses a class instance and a list of class instances as its attributes.

using System;
using System.Collections.Generic;
using UnityEngine.UIElements;

[Serializable]
public class MyClassWithData
{
    public int myInt;
    public float myFloat;
}

[UxmlElement]
public partial class MyElementWithData : VisualElement
{
    [UxmlAttribute]
    public MyClassWithData someData;

    [UxmlAttribute]
    public List<MyClassWithData> lotsOfData;
}

To support the class, declare a converter:

using UnityEditor.UIElements;

public class MyClassWithDataConverter : UxmlAttributeConverter<MyClassWithData>
{
    public override MyClassWithData FromString(string value)
    {
        // Split using a | so that comma (,) can be used by the list.
        var split = value.Split('|');

        return new MyClassWithData
        {
            myInt = int.Parse(split[0]),
            myFloat = float.Parse(split[1])
        };
    }

    public override string ToString(MyClassWithData value) => $"{value.myInt}|{value.myFloat}";
}

Example UXML:

<ui:UXML xmlns:ui="UnityEngine.UIElements">
    <MyElementWithData some-data="1|2.3" lots-of-data="1|2,3|4,5|6" />
</ui:UXML>

You can also use generic attribute converters. However, you must declare the attribute with the generic type. To use a type derived from a generic type, declare a new converter specifically for it. The following example uses a generic attribute converter and a custom property drawer to create a generic serialized dictionary:

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UIElements;

[Serializable]
public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, ISerializationCallbackReceiver
{
    [SerializeField] public List<TKey> keys = new List<TKey>();
    [SerializeField] public List<TValue> values = new List<TValue>();

    void ISerializationCallbackReceiver.OnAfterDeserialize() => TransferSerializedKeys();
    void ISerializationCallbackReceiver.OnBeforeSerialize() { }

    public void TransferSerializedKeys()
    {
        Clear();

        for (var i = 0; i < Math.Min(keys.Count, values.Count); i++)
        {
            this[keys[i]] = values[i];
        }
    }
}

[UxmlElement]
public partial class MyDictElement : VisualElement
{
    [UxmlAttribute]
    public SerializableDictionary<int, string> dictionaryIntString;

    [UxmlAttribute]
    public SerializableDictionary<int, int> dictionaryIntInt;

    [UxmlAttribute]
    public SerializableDictionary<string, string> dictionaryStringString;
}

Generic attribute converter:

using System;
using System.Globalization;
using System.Text;
using UnityEditor.UIElements;

public class SerializableDictionaryConverter<TKey, TValue> : UxmlAttributeConverter<SerializableDictionary<TKey, TValue>>
{
    static string ValueToString(object v) => Convert.ToString(v, CultureInfo.InvariantCulture);

    public override string ToString(SerializableDictionary<TKey, TValue> source)
    {
        var sb = new StringBuilder();
        foreach (var pair in source)
        {
            sb.Append($"{ValueToString(pair.Key)}|{ValueToString(pair.Value)},");
        }
        return sb.ToString();
    }

    public override SerializableDictionary<TKey, TValue> FromString(string source)
    {
        var result = new SerializableDictionary<TKey, TValue>();
        var items = source.Split(',');
        foreach (var item in items)
        {
            var fields = item.Split('|');
            var key = (TKey)Convert.ChangeType(fields[0], typeof(TKey));
            var value = (TValue)Convert.ChangeType(fields[1], typeof(TValue));

            result.keys.Add(key);
            result.values.Add(value);
        }
        result.TransferSerializedKeys();
        return result;
    }
}

Custom property drawer:

using UnityEditor;
using UnityEditor.UIElements;
using UnityEngine.UIElements;

[CustomPropertyDrawer(typeof(SerializableDictionary<,>))]
class SerializableDictionaryPropertyDrawer : PropertyDrawer
{
    SerializedProperty m_Property;
    SerializedProperty m_Keys;
    SerializedProperty m_Values;

    public override VisualElement CreatePropertyGUI(SerializedProperty property)
    {
        m_Property = property;
        m_Keys = property.FindPropertyRelative("keys");
        m_Values = property.FindPropertyRelative("values");

        var list = new ListView()
        {
            showAddRemoveFooter = true,
            showBorder = true,
            showAlternatingRowBackgrounds = AlternatingRowBackground.All,
            showFoldoutHeader = true,
            showBoundCollectionSize = false,
            reorderable = true,
            reorderMode = ListViewReorderMode.Animated,
            virtualizationMethod = CollectionVirtualizationMethod.DynamicHeight,
            headerTitle = property.displayName,
            bindingPath = m_Keys.propertyPath,
            overridingAddButtonBehavior = OnAddButton,
            bindItem = BindListItem,
        };
        return list;
    }

    void BindListItem(VisualElement item, int index)
    {
        item.Clear();

        item.Add(new PropertyField(m_Keys.GetArrayElementAtIndex(index)) { label = "Key" });
        item.Add(new PropertyField(m_Values.GetArrayElementAtIndex(index)) { label = "Value" });
        item.Bind(m_Property.serializedObject);
    }

    void OnAddButton(BaseListView baseListView, Button button)
    {
        m_Keys.InsertArrayElementAtIndex(m_Keys.arraySize);
        m_Values.InsertArrayElementAtIndex(m_Values.arraySize);
        m_Property.serializedObject.ApplyModifiedProperties();
    }
}

Public Methods