New binding mechanism: Expression tracking

src/Library/TerminalUI.Tests/BindingTests.cs

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+using TerminalUI.Controls;
+using TerminalUI.Extensions;
+using TerminalUI.Tests.Models;
+
+namespace TerminalUI.Tests;
+
+public class BindingTests
+{
+    private static string TestMapperMethodStatic(string s) => s.ToUpper();
+    private string TestMapperMethod(string s) => s.ToUpper();
+    
+    [Fact]
+    public void StaticCaptureMethodBinding_ByDefault_ShouldSetValue()
+    {
+        var testViewModel = new TestViewModel
+        {
+            Text = "test"
+        };
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+        
+        txtb1.Bind(
+            txtb1,
+            vm => TestMapperMethodStatic(vm.Text),
+            t => t.Text,
+            v => v);
+        
+        Assert.Equal("TEST", txtb1.Text);
+    }
+    
+    [Fact]
+    public void StaticCaptureMethodBinding_AfterUpdate_ShouldSetValue()
+    {
+        var testViewModel = new TestViewModel
+        {
+            Text = "test"
+        };
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+        
+        txtb1.Bind(
+            txtb1,
+            vm => TestMapperMethodStatic(vm.Text),
+            t => t.Text,
+            v => v);
+        
+        testViewModel.Text = "Updated";
+        
+        Assert.Equal("UPDATED", txtb1.Text);
+    }
+    
+    [Fact]
+    public void CaptureMethodBinding_ByDefault_ShouldSetValue()
+    {
+        var testViewModel = new TestViewModel
+        {
+            Text = "test"
+        };
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+        
+        txtb1.Bind(
+            txtb1,
+            vm => TestMapperMethod(vm.Text),
+            t => t.Text,
+            v => v);
+        
+        Assert.Equal("TEST", txtb1.Text);
+    }
+    
+    [Fact]
+    public void CaptureMethodBinding_AfterUpdate_ShouldSetValue()
+    {
+        var testViewModel = new TestViewModel
+        {
+            Text = "test"
+        };
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+        
+        txtb1.Bind(
+            txtb1,
+            vm => TestMapperMethod(vm.Text),
+            t => t.Text,
+            v => v);
+        
+        testViewModel.Text = "Updated";
+        
+        Assert.Equal("UPDATED", txtb1.Text);
+    }
+
+    [Fact]
+    public void FallbackValue_BindingFails_ShouldBeApplied()
+    {
+        var grid = new Grid<TestViewModel>();
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm.Items,
+            t => t.Text,
+            v => v.ToString(),
+            fallbackValue: "Fallback");
+
+        Assert.Equal("Fallback", txtb1.Text);
+    }
+
+    [Fact]
+    public void ConditionalExpression_WhenTrue_ShouldResultInTrueValue()
+    {
+        var grid = new Grid<TestViewModel>();
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm == null ? "null" : "not null",
+            t => t.Text,
+            v => v);
+
+        Assert.Equal("null", txtb1.Text);
+    }
+
+    [Fact]
+    public void ConditionalExpression_WhenFalse_ShouldResultInFalseValue()
+    {
+        var testViewModel = new TestViewModel();
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm == null ? "null" : "not null",
+            t => t.Text,
+            v => v);
+
+        Assert.Equal("not null", txtb1.Text);
+    }
+
+    [Fact]
+    public void ConditionalExpressionWithNestedValues_WhenTrue_ShouldResultInTrueNestedValue()
+    {
+        var testViewModel = new TestViewModel();
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm != null ? vm.Items.Count : -1,
+            t => t.Text,
+            v => v.ToString());
+
+        Assert.Equal("1", txtb1.Text);
+    }
+
+    [Fact]
+    public void ConditionalExpressionWithNestedValues_WhenFalse_ShouldResultInFalseNestedValue()
+    {
+        var testViewModel = new TestViewModel();
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm == null ? -1 : vm.Items.Count,
+            t => t.Text,
+            v => v.ToString());
+
+        Assert.Equal("1", txtb1.Text);
+    }
+
+    [Fact]
+    public void MixedBindingWithMethodCall_WhenRootChanged_ShouldUpdate()
+    {
+        var testViewModel = new TestViewModel();
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm.Items[0].GetNestedItem(0).OtherItems.Count,
+            t => t.Text,
+            v => v.ToString());
+
+        testViewModel.Items = new()
+        {
+            TestNestedCollectionItem.Create(4,
+                TestNestedCollectionItem.Create(
+                    6,
+                    TestNestedCollectionItem.Create(4)
+                ),
+                TestNestedCollectionItem.Create(1),
+                TestNestedCollectionItem.Create(2),
+                TestNestedCollectionItem.Create(3)
+            ),
+            TestNestedCollectionItem.Create(1),
+            TestNestedCollectionItem.Create(2),
+        };
+
+        Assert.Equal("6", txtb1.Text);
+    }
+
+    [Fact]
+    public void NestedPropertyBinding_WhenRootChanged_ShouldUpdateText()
+    {
+        var testViewModel = new TestViewModel();
+        var grid = new Grid<TestViewModel>
+        {
+            DataContext = testViewModel
+        };
+        var txtb1 = grid.CreateChild<TextBlock<TestViewModel>>();
+
+        txtb1.Bind(
+            txtb1,
+            vm => vm.Items.Count,
+            t => t.Text,
+            v => v.ToString());
+
+        testViewModel.Items = new List<TestNestedCollectionItem>
+        {
+            TestNestedCollectionItem.Create(4,
+                TestNestedCollectionItem.Create(
+                    6,
+                    TestNestedCollectionItem.Create(4)
+                ),
+                TestNestedCollectionItem.Create(1),
+                TestNestedCollectionItem.Create(2),
+                TestNestedCollectionItem.Create(3)
+            ),
+            TestNestedCollectionItem.Create(1),
+            TestNestedCollectionItem.Create(2),
+        };
+
+        Assert.Equal("3", txtb1.Text);
+    }
+}

src/Library/TerminalUI.Tests/GlobalUsings.cs

@@ -0,0 +1 @@
+global using Xunit;

src/Library/TerminalUI.Tests/Models/TestCollectionItem.cs

@@ -0,0 +1,10 @@
+namespace TerminalUI.Tests.Models;
+
+public class TestCollectionItem
+{
+    public List<TestItem>? Items1 { get; set; } = new()
+    {
+        new TestItem() {Name = "Name1"},
+        new TestItem() {Name = "Name2"},
+    };
+}

src/Library/TerminalUI.Tests/Models/TestItem.cs

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+namespace TerminalUI.Tests.Models;
+
+public class TestItem
+{
+    public string? Name { get; set; }
+}

src/Library/TerminalUI.Tests/Models/TestNestedCollectionItem.cs

@@ -0,0 +1,22 @@
+namespace TerminalUI.Tests.Models;
+
+public class TestNestedCollectionItem
+{
+    public List<TestNestedCollectionItem> Items { get; set; } = new();
+    public List<TestCollectionItem> OtherItems { get; set; } = new();
+
+    public TestNestedCollectionItem GetNestedItem(int index) => Items[index];
+    public TestCollectionItem GetSimpleItem(int index) => OtherItems[index];
+
+    public static TestNestedCollectionItem Create(int otherItemCount, params TestNestedCollectionItem[] items)
+    {
+        var collection = new TestNestedCollectionItem()
+        {
+            Items = items.ToList()
+        };
+        for (var i = 0; i < otherItemCount; i++)
+            collection.OtherItems.Add(new TestCollectionItem());
+
+        return collection;
+    }
+}

src/Library/TerminalUI.Tests/Models/TestViewModel.cs

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+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using PropertyChanged.SourceGenerator;
+
+namespace TerminalUI.Tests.Models;
+
+public sealed partial class TestViewModel : INotifyPropertyChanged
+{
+    [Notify] private List<TestNestedCollectionItem> _items;
+    [Notify] private string _text;
+
+    public TestViewModel()
+    {
+        _text = "Initial text";
+        _items = new List<TestNestedCollectionItem>
+        {
+            TestNestedCollectionItem.Create(
+                3,
+                TestNestedCollectionItem.Create(
+                    1, 
+                    TestNestedCollectionItem.Create(2)
+                ),
+                new()
+            )
+        };
+    }
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    private void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+        => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+}

src/Library/TerminalUI.Tests/TerminalUI.Tests.csproj

@@ -0,0 +1,33 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.0" />
+    <PackageReference Include="PropertyChanged.SourceGenerator" Version="1.0.8">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="xunit" Version="2.4.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector" Version="3.2.0">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\TerminalUI\TerminalUI.csproj" />
+  </ItemGroup>
+
+</Project>