Default Choice inputs to first option when no placeholder is set and custom choice is disabled

playground/Stress/Stress.AppHost/InteractionCommands.cs

@@ -135,6 +135,58 @@ public static IResourceBuilder<T> AddInteractionCommands<T>(this IResourceBuilde
 
                return CommandResults.Success();
            })
+           .WithCommand("choice-no-placeholder", "Choice with no placeholder", executeCommand: async commandContext =>
+           {
+               var interactionService = commandContext.ServiceProvider.GetRequiredService<IInteractionService>();
+               var dinnerInput = new InteractionInput
+               {
+                   Name = "Dinner",
+                   InputType = InputType.Choice,
+                   Label = "Dinner",
+                   Required = true,
+                   Options =
+                   [
+                       KeyValuePair.Create("pizza", "Pizza"),
+                       KeyValuePair.Create("fried-chicken", "Fried chicken"),
+                       KeyValuePair.Create("burger", "Burger")
+                   ]
+               };
+               var requirementsInput = new InteractionInput
+               {
+                   Name = "Requirements",
+                   InputType = InputType.Choice,
+                   Label = "Requirements",
+                   AllowCustomChoice = true,
+                   Options =
+                   [
+                       KeyValuePair.Create("vegetarian", "Vegetarian"),
+                       KeyValuePair.Create("vegan", "Vegan")
+                   ]
+               };
+               var result = await interactionService.PromptInputsAsync(
+                   title: "Text request",
+                   message: "Provide your name",
+                   inputs: [
+                       dinnerInput,
+                       requirementsInput
+                   ],
+                   cancellationToken: commandContext.CancellationToken);
+
+               if (result.Canceled)
+               {
+                   return CommandResults.Failure("Canceled");
+               }
+
+               var resourceLoggerService = commandContext.ServiceProvider.GetRequiredService<ResourceLoggerService>();
+               var logger = resourceLoggerService.GetLogger(commandContext.ResourceName);
+
+               foreach (var updatedInput in result.Data)
+               {
+                   logger.LogInformation("Input: {Label} = {Value}", updatedInput.Label, updatedInput.Value);
+               }
+
+               return CommandResults.Success();
+           })
            .WithCommand("input-interaction", "Input interactions", executeCommand: async commandContext =>
            {
                var interactionService = commandContext.ServiceProvider.GetRequiredService<IInteractionService>();

src/Aspire.Dashboard/Model/Interaction/InputViewModel.cs

@@ -46,6 +46,13 @@ public void SetInput(InteractionInput input)
                 .ToList();
 
             SelectOptions = optionsVM;
+
+            // Default to the first option if no placeholder is set, the value is empty, and custom choice is disabled.
+            // This is done so the input model value matches frontend behavior (FluentSelect defaults to the first option)
+            if (string.IsNullOrEmpty(input.Placeholder) && string.IsNullOrEmpty(input.Value) && optionsVM.Count > 0 && !input.AllowCustomChoice)
+            {
+                input.Value = optionsVM[0].Id;
+            }
         }
     }
 

tests/Aspire.Dashboard.Components.Tests/Model/InputViewModelTests.cs

@@ -0,0 +1,181 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Dashboard.Model.Interaction;
+using Aspire.DashboardService.Proto.V1;
+using Xunit;
+
+namespace Aspire.Dashboard.Components.Tests.Model;
+
+public class InputViewModelTests
+{
+    [Fact]
+    public void InputViewModel_ChoiceWithoutPlaceholder_DefaultsToFirstOption()
+    {
+        // Arrange
+        var input = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice,
+        };
+        input.Options.Add("red", "Red");
+        input.Options.Add("blue", "Blue");
+        input.Options.Add("green", "Green");
+
+        // Act
+        var viewModel = new InputViewModel(input);
+
+        // Assert
+        Assert.Equal("red", viewModel.Value);
+    }
+
+    [Fact]
+    public void InputViewModel_ChoiceWithPlaceholder_DoesNotDefaultToFirstOption()
+    {
+        // Arrange
+        var input = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice,
+            Placeholder = "Select a color"
+        };
+        input.Options.Add("red", "Red");
+        input.Options.Add("blue", "Blue");
+        input.Options.Add("green", "Green");
+
+        // Act
+        var viewModel = new InputViewModel(input);
+
+        // Assert - proto strings default to empty string, not null
+        Assert.True(string.IsNullOrEmpty(viewModel.Value));
+    }
+
+    [Fact]
+    public void InputViewModel_ChoiceWithExistingValue_KeepsExistingValue()
+    {
+        // Arrange
+        var input = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice,
+            Value = "blue"
+        };
+        input.Options.Add("red", "Red");
+        input.Options.Add("blue", "Blue");
+        input.Options.Add("green", "Green");
+
+        // Act
+        var viewModel = new InputViewModel(input);
+
+        // Assert
+        Assert.Equal("blue", viewModel.Value);
+    }
+
+    [Fact]
+    public void InputViewModel_ChoiceWithEmptyOptions_DoesNotSetValue()
+    {
+        // Arrange
+        var input = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice
+        };
+
+        // Act
+        var viewModel = new InputViewModel(input);
+
+        // Assert - proto strings default to empty string, not null
+        Assert.True(string.IsNullOrEmpty(viewModel.Value));
+    }
+
+    [Fact]
+    public void InputViewModel_NonChoiceInput_DoesNotSetValue()
+    {
+        // Arrange
+        var input = new InteractionInput
+        {
+            Label = "Enter Text",
+            InputType = InputType.Text
+        };
+
+        // Act
+        var viewModel = new InputViewModel(input);
+
+        // Assert - proto strings default to empty string, not null
+        Assert.True(string.IsNullOrEmpty(viewModel.Value));
+    }
+
+    [Fact]
+    public void SetInput_ChoiceWithoutPlaceholder_DefaultsToFirstOption()
+    {
+        // Arrange
+        var initialInput = new InteractionInput
+        {
+            Label = "Enter Text",
+            InputType = InputType.Text
+        };
+        var viewModel = new InputViewModel(initialInput);
+
+        var choiceInput = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice
+        };
+        choiceInput.Options.Add("red", "Red");
+        choiceInput.Options.Add("blue", "Blue");
+
+        // Act
+        viewModel.SetInput(choiceInput);
+
+        // Assert
+        Assert.Equal("red", viewModel.Value);
+    }
+
+    [Fact]
+    public void SetInput_ChoiceWithPlaceholder_DoesNotDefaultToFirstOption()
+    {
+        // Arrange
+        var initialInput = new InteractionInput
+        {
+            Label = "Enter Text",
+            InputType = InputType.Text
+        };
+        var viewModel = new InputViewModel(initialInput);
+
+        var choiceInput = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice,
+            Placeholder = "Select a color"
+        };
+        choiceInput.Options.Add("red", "Red");
+        choiceInput.Options.Add("blue", "Blue");
+
+        // Act
+        viewModel.SetInput(choiceInput);
+
+        // Assert - proto strings default to empty string, not null
+        Assert.True(string.IsNullOrEmpty(viewModel.Value));
+    }
+
+    [Fact]
+    public void InputViewModel_ChoiceWithAllowCustomChoice_DoesNotDefaultToFirstOption()
+    {
+        // Arrange
+        var input = new InteractionInput
+        {
+            Label = "Choose Color",
+            InputType = InputType.Choice,
+            AllowCustomChoice = true
+        };
+        input.Options.Add("red", "Red");
+        input.Options.Add("blue", "Blue");
+        input.Options.Add("green", "Green");
+
+        // Act
+        var viewModel = new InputViewModel(input);
+
+        // Assert - When AllowCustomChoice is true, value should not default
+        Assert.True(string.IsNullOrEmpty(viewModel.Value));
+    }
+}