import from UniRx and some modified.

Assets/UniRx.Async/Triggers/AsyncFixedUpdateTrigger.cs

@@ -0,0 +1,41 @@
+
+#if CSHARP_7_OR_LATER || (UNITY_2018_3_OR_NEWER && (NET_STANDARD_2_0 || NET_4_6))
+#pragma warning disable CS1591 // Missing XML comment for publicly visible type or member
+
+using System.Collections.Generic;
+using System.Threading;
+using UnityEngine;
+using UnityEngine.EventSystems;
+
+namespace UniRx.Async.Triggers
+{
+    [DisallowMultipleComponent]
+    public class AsyncFixedUpdateTrigger : AsyncTriggerBase
+    {
+        AsyncTriggerPromise<AsyncUnit> fixedUpdate;
+        AsyncTriggerPromiseDictionary<AsyncUnit> fixedUpdates;
+
+
+        protected override IEnumerable<ICancelablePromise> GetPromises()
+        {
+            return Concat(fixedUpdate, fixedUpdates);
+        }
+
+
+        void FixedUpdate()
+        {
+            TrySetResult(fixedUpdate, fixedUpdates, AsyncUnit.Default);
+        }
+
+
+        public UniTask FixedUpdateAsync(CancellationToken cancellationToken = default(CancellationToken))
+        {
+            return GetOrAddPromise(ref fixedUpdate, ref fixedUpdates, cancellationToken);
+        }
+
+
+    }
+}
+
+#endif
+