Merge pull request #184 from Unity-Technologies/siyaoH/1.17/gc

fix gc

README-ZH.md

 #### 八、移动设备优化
 目前在默认情况下，为了保证流畅度，项目在各个平台上均会以最高的刷新频率运行。不过您可以通过在代码中设置```UIWidgetsGlobalConfiguration.EnableAutoAdjustFramerate = true```的方式来开启自动降帧的功能：该功能开启后，在UI内容不变的情况下我们将降低项目的刷新率来降低耗电。
 
-在移动设备上UI绘制的流畅度受到GC影响较大。项目默认会开启OnDemandGC来接管并优化整体GC效果。如果您不需要GC被UIWidgets控制，请在代码中设置```UIWidgetsGlobalConfiguration.EnableIncrementalGC = false```。
-
+在移动设备上UI绘制的流畅度受到GC影响较大。如有卡顿，例如滑动掉帧。可开启OnDemandGC, UIWidgets将接管并优化整体GC效果，请在代码中设置```UIWidgetsGlobalConfiguration.EnableIncrementalGC = true```,并开启```Project Setting -> Player -> Other Settings -> Use incremental GC```。
 
 ## 调试UIWidgets应用程序
 

README.md

 #### Performance Optimization on Mobile devices
 By setting ```UIWidgetsGlobalConfiguration.EnableAutoAdjustFramerate = true``` in your project, UIWidgets will drop the frame rate of your App to 0 if the UI contents of UIWidgetsPanel is not changed for some time. This will help to prevent battery drain on mobile devices significantly. Note that this feature is disabled by default.
 
-Long time garbage collection may cause App to stuck frequently. In UIWidgets we enable incremental garbage collection to avoid it. However, you can disable this feature by setting ```UIWidgetsGlobalConfiguration.EnableIncrementalGC = false```.
+Long time garbage collection may cause App to stuck frequently. You can enable incremental garbage collection to avoid it. You can enable this feature by setting ```UIWidgetsGlobalConfiguration.EnableIncrementalGC = true```, and enabling ```Project Setting -> Player -> Other Settings -> Use incremental GC```.
 
 ## Debug UIWidgets Application
 

com.unity.uiwidgets/Runtime/engine/UIWidgetsGlobalConfiguration.cs

         //disable auto adjust framerate by default
         public static bool EnableAutoAdjustFramerate = false;
 
-        //enable incremental gc by default
-        public static bool EnableIncrementalGC = true;
+        //disable incremental gc by default
+        public static bool EnableIncrementalGC = false;
         
         //disable debug at runtime by default
         public static bool EnableDebugAtRuntime = false;

com.unity.uiwidgets/Runtime/engine/UIWidgetsPanel.cs

             if (UIWidgetsGlobalConfiguration.EnableIncrementalGC)
             {
                 GarbageCollector.GCMode = GarbageCollector.Mode.Disabled;
-                Application.lowMemory += GC.Collect;
+            }
+        }
+
+        void TryDisableOnDemandGC() 
+        {
+            if (UIWidgetsGlobalConfiguration.EnableIncrementalGC)
+            {
+                GarbageCollector.GCMode = GarbageCollector.Mode.Enabled;
             }
         }
 
             else if (mem >= nextCollectAt)
             {
                 // Trigger incremental GC
+                GarbageCollector.GCMode = GarbageCollector.Mode.Enabled;
+                GarbageCollector.GCMode = GarbageCollector.Mode.Disabled;
             }
 
             lastFrameMemory = mem;
             
 #if !UNITY_EDITOR
             TryEnableOnDemandGC();
+            Application.lowMemory += () => {
+                TryDisableOnDemandGC();
+                GC.Collect();
+                TryEnableOnDemandGC();
+            };
 #endif
 
             base.OnEnable();
             _wrapper = null;
             texture = null;
             Input_OnDisable();
+#if !UNITY_EDITOR
+            TryDisableOnDemandGC();
+#endif
             base.OnDisable();
         }