Version: 2017.2

SceneManager.UnloadSceneAsync

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public static AsyncOperation UnloadSceneAsync (int sceneBuildIndex);
public static AsyncOperation UnloadSceneAsync (string sceneName);
public static AsyncOperation UnloadSceneAsync (SceneManagement.Scene scene);

Parameters

sceneBuildIndex Index of the Scene in BuildSettings.
sceneName Name or path of the Scene to unload.
scene Scene to unload.

Returns

AsyncOperation Use the AsyncOperation to determine if the operation has completed.

Description

Destroys all GameObjects associated with the given Scene and removes the Scene from the SceneManager.

The given Scene name can either be the full Scene path, the path shown in the Build Settings window or just the Scene name. If only the Scene name is given this will unload the first Scene in the list that matches. If you have multiple Scenes with same name but different paths, you should use the full Scene path. Examples of supported formats:
"Assets/Scenes/Scene1.unity"
"Scenes/Scene1"
"Scene1"

Note: This is case-insensitive and due to it being async there are no guarantees about completion time.
Note: That assets are currently not unloaded. In order to free up asset memory call Resources.UnloadAllUnusedAssets.