Explicitly implement SetParametersAsync

src/Components/Blazor/testassets/StandaloneApp/Pages/FetchData.razor

@@ -48,10 +48,9 @@ else
 
     WeatherForecast[] forecasts;
 
-    public override Task SetParametersAsync(ParameterCollection parameters)
+    protected override void OnParametersSetting()
     {
         StartDate = DateTime.Now;
-        return base.SetParametersAsync(parameters);
     }
 
     protected override async Task OnParametersSetAsync()

src/Components/Components/src/ComponentBase.cs

@@ -78,15 +78,30 @@ protected virtual Task OnInitializedAsync()
 
         /// <summary>
         /// Method invoked when the component has received parameters from its parent in
-        /// the render tree, and the incoming values have been assigned to properties.
+        /// the render tree, before the incoming values have been assigned to properties.
+        /// </summary>
+        protected virtual void OnParametersSetting()
+        {
+        }
+
+        /// <summary>
+        /// Method invoked when the component has received parameters from its parent in
+        /// the render tree, before the incoming values have been assigned to properties.
+        /// </summary>
+        /// <returns>A <see cref="Task"/> representing any asynchronous operation.</returns>
+        protected virtual Task OnParametersSettingAsync() => Task.CompletedTask;
+
+        /// <summary>
+        /// Method invoked when the component has received parameters from its parent in
+        /// the render tree, after the incoming values have been assigned to properties.
         /// </summary>
         protected virtual void OnParametersSet()
         {
         }
 
         /// <summary>
         /// Method invoked when the component has received parameters from its parent in
-        /// the render tree, and the incoming values have been assigned to properties.
+        /// the render tree, after the incoming values have been assigned to properties.
         /// </summary>
         /// <returns>A <see cref="Task"/> representing any asynchronous operation.</returns>
         protected virtual Task OnParametersSetAsync()
@@ -175,22 +190,22 @@ void IComponent.Configure(RenderHandle renderHandle)
         /// Method invoked to apply initial or updated parameters to the component.
         /// </summary>
         /// <param name="parameters">The parameters to apply.</param>
-        public virtual Task SetParametersAsync(ParameterCollection parameters)
+        Task IComponent.SetParametersAsync(ParameterCollection parameters)
         {
-            parameters.SetParameterProperties(this);
             if (!_initialized)
             {
                 _initialized = true;
 
-                return RunInitAndSetParametersAsync();
+                return RunInitAndSetParametersAsync(parameters);
             }
             else
             {
-                return CallOnParametersSetAsync();
+
+                return SetParametersCoreAsync(parameters);
             }
         }
 
-        private async Task RunInitAndSetParametersAsync()
+        private async Task RunInitAndSetParametersAsync(ParameterCollection parameters)
         {
            OnInitialized();
             var task = OnInitializedAsync();
@@ -223,9 +238,35 @@ private async Task RunInitAndSetParametersAsync()
                 // Don't call StateHasChanged here. CallOnParametersSetAsync should handle that for us.
             }
 
+            await SetParametersCoreAsync(parameters);
+        }
+
+        private async Task SetParametersCoreAsync(ParameterCollection parameters)
+        {
+            await CallOnParametersSettingAsync();
+            parameters.SetParameterProperties(this);
             await CallOnParametersSetAsync();
         }
 
+        private Task CallOnParametersSettingAsync()
+        {
+            OnParametersSetting();
+            var task = OnParametersSettingAsync();
+            // If no async work is to be performed, i.e. the task has already ran to completion
+            // or was canceled by the time we got to inspect it, avoid going async and re-invoking
+            // StateHasChanged at the culmination of the async work.
+            var shouldAwaitTask = task.Status != TaskStatus.RanToCompletion &&
+                task.Status != TaskStatus.Canceled;
+
+            // We always call StateHasChanged here as we want to trigger a rerender after OnParametersSet and
+            // the synchronous part of OnParametersSetAsync has run.
+            StateHasChanged();
+
+            return shouldAwaitTask ?
+                CallStateHasChangedOnAsyncCompletion(task) :
+                Task.CompletedTask;
+        }
+
         private Task CallOnParametersSetAsync()
         {
             OnParametersSet();

src/Components/Components/src/Forms/InputComponents/InputBase.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq.Expressions;
-using System.Threading.Tasks;
 
 namespace Microsoft.AspNetCore.Components.Forms
 {
@@ -166,12 +165,9 @@ protected string CssClass
             }
         }
 
-
         /// <inheritdoc />
-        public override Task SetParametersAsync(ParameterCollection parameters)
+        protected override void OnParametersSet()
         {
-            parameters.SetParameterProperties(this);
-
             if (EditContext == null)
             {
                 // This is the first run
@@ -204,9 +200,6 @@ public override Task SetParametersAsync(ParameterCollection parameters)
                 throw new InvalidOperationException($"{GetType()} does not support changing the " +
                     $"{nameof(Forms.EditContext)} dynamically.");
             }
-
-            // For derived components, retain the usual lifecycle with OnInit/OnParametersSet/etc.
-            return base.SetParametersAsync(ParameterCollection.Empty);
         }
     }
 }

src/Components/test/testassets/BasicTestApp/RouterTest/WithParameters.razor

@@ -1,5 +1,6 @@
 @page "/WithParameters/Name/{firstName}"
 @page "/WithParameters/Name/{firstName}/LastName/{lastName}"
+@implements IComponent
 <div id="test-info">Your full name is @FirstName @LastName.</div>
 <Links />
 
@@ -9,11 +10,10 @@
 
     [Parameter] string LastName { get ; set; }
 
-    public override Task SetParametersAsync(ParameterCollection parameters)
+    protected override void OnParametersSetting()
     {
         // Manually reset parameters to defaults so we don't retain any from an earlier URL
         FirstName = default;
         LastName = default;
-        return base.SetParametersAsync(parameters);
     }
 }