Load navigation state saved by JsonFilePersistenceProvider

Navigation.Test/JsonFilePersistenceProviderTests.cs

@@ -0,0 +1,60 @@
+// Copyright (c) 2023-2026 ktsu-dev contributors
+
+namespace ktsu.Navigation.Test;
+
+using ktsu.Navigation.Models;
+using ktsu.Navigation.Services;
+
+[TestClass]
+public class JsonFilePersistenceProviderTests
+{
+	private string? _filePath;
+
+	[TestInitialize]
+	public void Setup() => _filePath = Path.Combine(Path.GetTempPath(), $"navigation-{Guid.NewGuid():N}.json");
+
+	[TestCleanup]
+	public void Cleanup()
+	{
+		if (File.Exists(_filePath))
+		{
+			File.Delete(_filePath);
+		}
+	}
+
+	[TestMethod]
+	public async Task SaveThenLoad_IntoNewNavigation_RestoresCurrentAndStacks()
+	{
+		// Arrange
+		JsonFilePersistenceProvider<NavigationItem> provider = new(_filePath!);
+		Navigation<NavigationItem> navigation = new(null, provider);
+		navigation.NavigateTo(new NavigationItem("a", "A"));
+		navigation.NavigateTo(new NavigationItem("b", "B"));
+		navigation.NavigateTo(new NavigationItem("c", "C"));
+		navigation.GoBack();
+		await navigation.SaveStateAsync().ConfigureAwait(false);
+
+		// Act
+		Navigation<NavigationItem> restored = new(null, provider);
+		bool loaded = await restored.LoadStateAsync().ConfigureAwait(false);
+
+		// Assert
+		Assert.IsTrue(loaded);
+		Assert.AreEqual(3, restored.Count);
+		Assert.AreEqual("b", restored.Current?.Id);
+		Assert.AreEqual("B", restored.Current?.DisplayName);
+		Assert.AreEqual("a", string.Join(",", restored.GetBackStack().Select(item => item.Id)));
+		Assert.AreEqual("c", string.Join(",", restored.GetForwardStack().Select(item => item.Id)));
+	}
+
+	[TestMethod]
+	public async Task LoadStateAsync_UnreadableData_ReturnsNull()
+	{
+		// Arrange
+		await File.WriteAllTextAsync(_filePath!, """{"items":[{"id":"a","displayName":"A"}],"currentIndex":5}""").ConfigureAwait(false);
+		JsonFilePersistenceProvider<NavigationItem> provider = new(_filePath!);
+
+		// Act & Assert
+		Assert.IsNull(await provider.LoadStateAsync().ConfigureAwait(false));
+	}
+}

Navigation/Models/NavigationState.cs

@@ -5,6 +5,7 @@ namespace ktsu.Navigation.Models;
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.Json.Serialization;
 using ktsu.Navigation.Contracts;
 
 /// <summary>
@@ -35,6 +36,18 @@ public NavigationState(IEnumerable<T> items, int currentIndex)
 		CreatedAt = DateTime.UtcNow;
 	}
 
+	/// <summary>
+	/// Initializes a new instance of the <see cref="NavigationState{T}"/> class when deserializing.
+	/// System.Text.Json requires each constructor parameter to have the same type as the property it binds to.
+	/// </summary>
+	/// <param name="items">The items in the navigation stack</param>
+	/// <param name="currentIndex">The index of the current item</param>
+	[JsonConstructor]
+	public NavigationState(IReadOnlyList<T> items, int currentIndex)
+		: this((IEnumerable<T>)items, currentIndex)
+	{
+	}
+
 	/// <inheritdoc />
 	public IReadOnlyList<T> Items { get; }
 

Navigation/Services/JsonFilePersistenceProvider.cs

@@ -77,6 +77,11 @@ public async Task SaveStateAsync(INavigationState<T> state, CancellationToken ca
 			// If file read fails, return null
 			return null;
 		}
+		catch (ArgumentException)
+		{
+			// If the saved state is invalid (for example, a current index outside the items), return null
+			return null;
+		}
 	}
 
 	/// <inheritdoc />