Unity3D: Detect when play mode changes to what

Unity_NewerThan2017_1.cs

// For Unity versions newer than 2017.1
using UnityEditor;

[InitializeOnLoad]
public class DetectPlayModeChanges {

    static DetectPlayModeChanges() {
        EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
    }

    private static void OnPlayModeStateChanged(PlayModeStateChange state) {
        switch (state) {
            case PlayModeStateChange.ExitingEditMode:
                // Do whatever before entering play mode
                break;
            case PlayModeStateChange.EnteredPlayMode:
                // Do whatever after entering play mode
                break;
            case PlayModeStateChange.ExitingPlayMode:
                // Do whatever before returning to edit mode
                break;
            case PlayModeStateChange.EnteredEditMode:
                // Do whatever after returning to edit mode
                break;
        }
    }
}

Unity_UpTo2017_1.cs

// For Unity versions up to 2017.1
using UnityEditor;

public static class EditorState {

    public static bool willEnterPlayMode {
        get { return !EditorApplication.isPlaying
                     && EditorApplication.isPlayingOrWillChangePlaymode; }
    }

    public static bool didEnterPlayMode {
        get { return EditorApplication.isPlaying
                     && EditorApplication.isPlayingOrWillChangePlaymode; }
    }

    public static bool willExitPlayMode {
        get { return EditorApplication.isPlaying
                     && !EditorApplication.isPlayingOrWillChangePlaymode; }
    }

    public static bool didExitPlayMode {
        get { return !EditorApplication.isPlaying
                     && !EditorApplication.isPlayingOrWillChangePlaymode; }
    }
}

[InitializeOnLoad]
public class DetectPlayModeChanges {

    static DetectPlayModeChanges() {
        EditorApplication.playmodeStateChanged += OnPlayModeStateChanged;
    }

    private static void OnPlayModeStateChanged() {
        if (EditorState.willEnterPlayMode) {
            // Do whatever before entering play mode
        }
        if (EditorState.didEnterPlayMode) {
            // Do whatever after entering play mode
        }
        if (EditorState.willExitPlayMode) {
            // Do whatever before returning to edit mode
        }
        if (EditorState.didExitPlayMode) {
            // Do whatever after returning to edit mode
        }
    }
}

Works very well on both Unity 5.6 and 2018.3. Thank you for sharing this!