Fix .NET unloading issue

addons/terrain-editing/TerrainEditingControls+Editing.cs

@@ -6,7 +6,7 @@ public partial class TerrainEditingControls
 	(TilePos, TilePos)? _selection = null;
 
 	Material _editToolMaterial;
-	void OnEditingReady()
+	public override void _EnterTree()
 	{
 		_editToolMaterial = new StandardMaterial3D {
 			VertexColorUseAsAlbedo = true,

addons/terrain-editing/TerrainEditingControls.cs

@@ -5,12 +5,11 @@ public partial class TerrainEditingControls
 	public (ToolMode , Button)[] ToolModeButtons     { get; private set; }
 	public (ToolShape, Button)[] ToolShapeButtons    { get; private set; }
 	public Button[]              PaintTextureButtons { get; private set; }
-
 	public Slider                DrawSizeSlider      { get; private set; }
 
-	ToolMode  _toolMode;
-	ToolShape _toolShape;
-	int       _texture;
+	ToolMode  _toolMode  = ToolMode.Height;
+	ToolShape _toolShape = ToolShape.Circle;
+	int       _texture   = 1;
 
 	public ToolMode  ToolMode  { get => _toolMode ; set => SetToolMode (value); }
 	public ToolShape ToolShape { get => _toolShape; set => SetToolShape(value); }
@@ -52,16 +51,17 @@ public partial class TerrainEditingControls
 		DrawSizeSlider = GetNode<Slider>("SizeSlider");
 		DrawSizeSlider.ValueChanged += (_) => drawSizeLabel.Text = $"{DrawSize}";
 
-		SetToolMode(ToolMode.Height);
-		SetToolShape(ToolShape.Circle);
-		SetTexture(1);
-
-		OnEditingReady();
+		SetToolMode(_toolMode);
+		SetToolShape(_toolShape);
+		SetTexture(_texture);
 	}
 
 
 	void SetToolMode(ToolMode value)
 	{
+		// Ignore if _Ready hasn't been called yet.
+		if (ToolModeButtons == null) return;
+
 		foreach (var (mode, button) in ToolModeButtons)
 			button.Flat = button.ButtonPressed = value != mode;
 		foreach (var button in PaintTextureButtons)
@@ -71,6 +71,9 @@ public partial class TerrainEditingControls
 
 	void SetToolShape(ToolShape value)
 	{
+		// Ignore if _Ready hasn't been called yet.
+		if (ToolShapeButtons == null) return;
+
 		foreach (var (shape, button) in ToolShapeButtons)
 			button.Flat = button.ButtonPressed = value != shape;
 		DrawSizeSlider.Editable = value != ToolShape.Corner;
@@ -79,6 +82,9 @@ public partial class TerrainEditingControls
 
 	void SetTexture(int value)
 	{
+		// Ignore if _Ready hasn't been called yet.
+		if (PaintTextureButtons == null) return;
+
 		if ((value < 1) || (value > PaintTextureButtons.Length))
 			throw new ArgumentOutOfRangeException(nameof(value));
 		foreach (var (i, button) in PaintTextureButtons.Select((b, i) => (i, b)))

addons/terrain-editing/TerrainEditingPlugin.cs

@@ -1,9 +1,13 @@
 #if TOOLS
-
 [Tool]
 public partial class TerrainEditingPlugin
 	: EditorPlugin
 {
+	const string ScenePath = "res://addons/terrain-editing/TerrainEditingControls.tscn";
+	// The container to which the editing controls get added to when Terrain is selected.
+	const CustomControlContainer Container = CustomControlContainer.SpatialEditorSideRight;
+
+
 	TerrainEditingControls _controls;
 
 	public override bool _Handles(GodotObject obj)
@@ -11,24 +15,25 @@ public partial class TerrainEditingPlugin
 
 	public override void _EnterTree()
 	{
-		var scene = GD.Load<PackedScene>("res://addons/terrain-editing/TerrainEditingControls.tscn");
+		var scene = GD.Load<PackedScene>(ScenePath);
 		_controls = scene.Instantiate<TerrainEditingControls>();
 	}
 
 	public override void _ExitTree()
 	{
 		if (_controls == null) return;
-		_controls.QueueFree();
+		if (_controls.GetParent() != null)
+			RemoveControlFromContainer(Container, _controls);
+		_controls.Free();
 		_controls = null;
 	}
 
 	public override void _MakeVisible(bool visible)
 	{
-		var container = CustomControlContainer.SpatialEditorSideRight;
 		if (visible)
-			AddControlToContainer(container, _controls);
-		else if (_controls != null)
-			RemoveControlFromContainer(container, _controls);
+			AddControlToContainer(Container, _controls);
+		else if (_controls.GetParent() != null)
+			RemoveControlFromContainer(Container, _controls);
 	}
 }
 #endif