To add your own support for file formats that aren’t natively supported by Unity, you can use a ScriptedImporter to write custom asset importers in C#.
A scripted importer is a class that inherits from the abstract class ScriptedImporter and has the [ScriptedImporter] attribute. This registers your custom importer to handle one or more file extensions. When Unity detects a file that matches the registered file extensions as being new or changed, it invokes the method OnImportAsset of your custom importer.
Important: Scripted importers can’t handle a file extension that Unity already natively handles. You can use the overrideExts parameter to override this behavior and add the file extension for the existing importer. For a list of files Unity natively supports, refer to Supported asset type reference.
Once you have added a ScriptedImporter script to a project, you can use it the same way as any other file type supported by Unity. For more information, refer to Introduction to importing assets.
The following code example imports asset files with the extension cube into a prefabAn asset type that allows you to store a GameObject complete with components and properties. The prefab acts as a template from which you can create new object instances in the scene. More info
See in Glossary with a cube primitive as the main asset and a default material and color. It then assigns its position from a value read from the asset file:
using UnityEngine;
using UnityEditor.AssetImporters;
using System.IO;
// The importer is registered with Unity's asset pipeline by placing the ScriptedImporter attribute on the
// CubeImporter class. The CubeImporter class implements the abstract ScriptedImporter base class.
[ScriptedImporter(1, "cube")]
public class CubeImporter : ScriptedImporter
{
public float m_Scale = 1;
// The ctx argument contains both input and output data for the import event
public override void OnImportAsset(AssetImportContext ctx)
{
var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
var position = JsonUtility.FromJson<Vector3>(File.ReadAllText(ctx.assetPath));
cube.transform.position = position;
cube.transform.localScale = new Vector3(m_Scale, m_Scale, m_Scale);
// 'cube' is a GameObject and is automatically converted into a prefab.
// Only the 'Main Asset' is eligible to become a prefab.
ctx.AddObjectToAsset("main obj", cube);
ctx.SetMainObject(cube);
var material = new Material(Shader.Find("Standard"));
material.color = Color.red;
// Assets must be assigned a unique identifier string consistent across imports.
ctx.AddObjectToAsset("my Material", material);
// Assets that are not passed into the context as import outputs must be destroyed.
var tempMesh = new Mesh();
DestroyImmediate(tempMesh);
}
}
For more information, refer to the AssetImporters.ScriptedImporter API documentation.
To create a custom import settings window for your scripted importer, create a class that inherits from ScriptedImporterEditor and decorate it with the [CustomEditor] attribute. For example:
using UnityEditor;
using UnityEditor.AssetImporters;
using UnityEditor.SceneManagement;
using UnityEngine;
[CustomEditor(typeof(CubeImporter))]
public class CubeImporterEditor: ScriptedImporterEditor
{
public override void OnInspectorGUI()
{
var colorShift = new GUIContent("Color Shift");
var prop = serializedObject.FindProperty("m_ColorShift");
EditorGUILayout.PropertyField(prop, colorShift);
base.ApplyRevertGUI();
}
}
Unity uses scripted importers for the following file formats:
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