OdinValueDrawer<T> class

public class MyCustomBaseType
{

}

public class MyCustomType : MyCustomBaseType
{

}

// Remember to wrap your custom attribute drawer within a #if UNITY_EDITOR condition, or locate the file inside an Editor folder.

public sealed class MyCustomBaseTypeDrawer<T> : OdinValueDrawer<T> where T : MyCustomBaseType
{
    protected override void DrawPropertyLayout(IPropertyValueEntry<T> entry, GUIContent label)
    {
        T value = entry.SmartValue;
        // Draw your custom drawer here using GUILayout and EditorGUILAyout.
    }
}

// Usage:
// Both values will be drawn using the MyCustomBaseTypeDrawer
public class MyComponent : SerializedMonoBehaviour
{
    public MyCustomBaseType A;

    public MyCustomType B;
}

Odin uses multiple drawers to draw any given property, and the order in which these drawers are called are defined using the DrawerPriorityAttribute. Your custom drawer injects itself into this chain of drawers based on its DrawerPriorityAttribute. If no DrawerPriorityAttribute is defined, a priority is generated automatically based on the type of the drawer. Each drawer can ether choose to draw the property or not, or pass on the responsibility to the next drawer by calling CallNextDrawer(). An example of this is provided in the documentation for OdinAttributeDrawer<TAttribute, TValue>.

This means that there is no guarantee that your drawer will be called, sins other drawers could have a higher priority than yours and choose not to call CallNextDrawer().

To avoid this, you can tell Odin, that your drawer is a PrependDecorator or an AppendDecorator drawer (see ) as shown in the example shows below. Prepend and append decorators are always drawn and are also ordered by the .

Note that Odin's have full support for generic class constraints, and if that is not enough, you can also add additional type constraints by overriding CanDrawTypeFilter(Type type).

Also note that all custom property drawers needs to handle cases where the label provided by the DrawPropertyLayout is null, otherwise exceptions will be thrown when in cases where the label is hidden. For instance when [HideLabel] is used, or the property is drawn within a list where labels are also not shown.

// [OdinDrawer(OdinDrawerBehaviour.DrawProperty)] // default
// [OdinDrawer(OdinDrawerBehaviour.AppendDecorator)]
[OdinDrawer(OdinDrawerBehaviour.PrependDecorator)]
[DrawerPriority(DrawerPriorityLevel.AttributePriority)]
public sealed class MyCustomTypeDrawer<T> : OdinValueDrawer<T> where T : MyCustomType
{
    public override bool CanDrawTypeFilter(Type type)
    {
        return type != typeof(SomeType);
    }

    protected override void DrawPropertyLayout(IPropertyValueEntry<T> entry, GUIContent label)
    {
        T value = entry.SmartValue;
        // Draw property here.
    }
}