make sure texture/rendertexture/material has hideflags as HideAndDontSave.

Runtime/debugger/inspector_treeview.cs

 
         public static int GetIntProperty(Dictionary<string, object> properties, string name)
         {
-            object val;
-            properties.TryGetValue(name, out val);
+            object val = null;
+
+            if (properties != null) {
+                properties.TryGetValue(name, out val);
+            }
+
             if (val == null)
             {
                 return -1;

Runtime/editor/surface.cs

             }
 
             _guiTextureMat = new Material(guiTextureShader);
+            _guiTextureMat.hideFlags = HideFlags.HideAndDontSave;
             return _guiTextureMat;
         }
 
         void _createOrUpdateRenderTexture(Size size, double devicePixelRatio) {
             if (this._surface != null
                 && this._surface.size == size
-                && this._surface.devicePixelRatio == devicePixelRatio) {
+                && this._surface.devicePixelRatio == devicePixelRatio
+                && this._surface.getRenderTexture() != null) {
                 return;
             }
 
             }
 
             this._renderTexture = new RenderTexture(desc);
+            this._renderTexture.hideFlags = HideFlags.HideAndDontSave;
-            D.assert(this._renderTexture);
-            this._renderTexture = ObjectUtils.SafeDestroy(this._renderTexture);
-            
-            D.assert(this._canvas != null);
-            this._canvas = null;
+            if (this._renderTexture) {
+                this._renderTexture = ObjectUtils.SafeDestroy(this._renderTexture);
+            }
+
+            if (this._canvas != null) {
+                this._canvas.reset();
+                this._canvas = null;
+            }
         }
     }
 }

Runtime/flow/raster_cache.cs

             };
 
             var renderTexture = new RenderTexture(desc);
+            renderTexture.hideFlags = HideFlags.HideAndDontSave;
             
             var canvas = new CommandBufferCanvas(renderTexture, devicePixelRatio);
             canvas.translate((float) -bounds.left, (float) -bounds.top);

Runtime/ui/painting/canvas_impl.cs

             }
 
             mat = new Material(canvasShader);
+            mat.hideFlags = HideFlags.HideAndDontSave;
             _materials[op] = mat;
 
             if (op == BlendMode.srcOver) {
         }
 
         public void reset() {
+            foreach (var layer in this._layers) {
+                this._clearLayer(layer);
+            }
+
-            var bounds = Rect.fromLTWH(0, 0,
-                this._renderTexture.width / this._devicePixelRatio,
-                this._renderTexture.height / this._devicePixelRatio);
-            this._layers.Clear();
-            this._layers.Add(
-                new RenderLayer {
+            RenderLayer firstLayer;
+            if (this._layers.Count == 0) {
+                var bounds = Rect.fromLTWH(0, 0,
+                    this._renderTexture.width / this._devicePixelRatio,
+                    this._renderTexture.height / this._devicePixelRatio);
+                firstLayer = new RenderLayer {
-                }
-            );
+                };
+            } else {
+                D.assert(this._layers.Count > 0);
+                firstLayer = this._layers[0];
+                firstLayer = new RenderLayer {
+                    width = firstLayer.width,
+                    height = firstLayer.height,
+                    layerBounds = firstLayer.layerBounds,
+                };
+            }
+
+            this._layers.Clear();
+            this._layers.Add(firstLayer);
         }
 
         void _drawLayer(RenderLayer layer, CommandBuffer cmdBuf) {

Runtime/ui/painting/codec.cs

             }
 
             var texture = new Texture2D(2, 2);
+            texture.hideFlags = HideFlags.HideAndDontSave;
             texture.LoadImage(bytes);
             return Promise<Codec>.Resolved(new ImageCodec(new Image(texture)));
         }

Runtime/ui/painting/codec_gif.cs

                 }
 
                 var tex = new Texture2D(this._width, this._height, TextureFormat.BGRA32, false);
+                tex.hideFlags = HideFlags.HideAndDontSave;
                 tex.LoadRawTextureData(frameData.gifFrame.bytes);
                 tex.Apply();
 

Tests/Editor/CanvasAndLayers.cs

             }
 
             _guiTextureMat = new Material(guiTextureShader);
+            _guiTextureMat.hideFlags = HideFlags.HideAndDontSave;
             return _guiTextureMat;
         }
 

Tests/Editor/Widgets.cs

                     var rootWidget = this.loadAsset();
                     this.windowAdapter.attachRootWidget(rootWidget);
                 }
+                
+                if (GUILayout.Button("UnloadUnusedAssets")) {
+                    Resources.UnloadUnusedAssets();
+                }
             }
             else if (selected != this._selected || !this.hasInvoked) {
                 this._selected = selected;