Feat/deferred view updates

CHANGELOG.md

@@ -6,6 +6,7 @@ All notable changes to this repository are documented here.
 
 ### Added
 
+- Added `DeferViewUpdates()` for nested, exception-safe view update batching across standard and data-bound list variants.
 - Added per-monitor DPI font rescaling with non-compounding transitions, virtual-list safety, and preservation of explicit column widths.
 - Added a dedicated MSTest regression suite for `ObjectListView2022`, targeting .NET Framework 4.8.1.
 - Added behavioral coverage for filtering, sorting, grouping, fast/virtual lists, tree lists, check-state handling, Munger access, hot-item behavior, context-menu handling, state persistence, and performance-sensitive paths.

src/ObjectListView2022.Tests/DeferredViewUpdateTests.cs

@@ -0,0 +1,237 @@
+using System.ComponentModel;
+using System.Windows.Forms;
+using BrightIdeasSoftware;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace ObjectListView2022.Tests
+{
+    [STATestClass]
+    public class DeferredViewUpdateTests
+    {
+        [TestMethod]
+        public void DeferViewUpdates_DefersRebuildUntilScopeIsDisposed()
+        {
+            using var listView = CreateListView();
+            listView.SetObjects(new[] { new Model("first") });
+            Assert.AreEqual(1, listView.GetItemCount());
+
+            using (listView.DeferViewUpdates())
+            {
+                listView.SetObjects(new[] {
+                    new Model("first"),
+                    new Model("second"),
+                    new Model("third")
+                });
+
+                Assert.IsTrue(listView.Frozen);
+                Assert.AreEqual(1, listView.GetItemCount());
+            }
+
+            Assert.IsFalse(listView.Frozen);
+            Assert.AreEqual(3, listView.GetItemCount());
+        }
+
+        [TestMethod]
+        public void DeferViewUpdates_NestedScopesRebuildOnlyAfterOutermostScope()
+        {
+            using var listView = CreateListView();
+            listView.SetObjects(new[] { new Model("first") });
+
+            using (listView.DeferViewUpdates())
+            {
+                using (listView.DeferViewUpdates())
+                {
+                    listView.SetObjects(new[] {
+                        new Model("first"),
+                        new Model("second")
+                    });
+                }
+
+                Assert.IsTrue(listView.Frozen);
+                Assert.AreEqual(1, listView.GetItemCount());
+            }
+
+            Assert.IsFalse(listView.Frozen);
+            Assert.AreEqual(2, listView.GetItemCount());
+        }
+
+        [TestMethod]
+        public void DeferViewUpdates_NestedScopesCanBeDisposedOutOfOrder()
+        {
+            using var listView = CreateListView();
+            listView.SetObjects(new[] { new Model("first") });
+            var firstScope = listView.DeferViewUpdates();
+            var secondScope = listView.DeferViewUpdates();
+            listView.SetObjects(new[] {
+                new Model("first"),
+                new Model("second")
+            });
+
+            firstScope.Dispose();
+
+            Assert.IsTrue(listView.Frozen);
+            Assert.AreEqual(1, listView.GetItemCount());
+
+            secondScope.Dispose();
+
+            Assert.IsFalse(listView.Frozen);
+            Assert.AreEqual(2, listView.GetItemCount());
+        }
+
+        [TestMethod]
+        public void DeferViewUpdates_PreservesExistingFreezeUntilCallerUnfreezes()
+        {
+            using var listView = CreateListView();
+            listView.SetObjects(new[] { new Model("first") });
+            listView.Freeze();
+
+            using (listView.DeferViewUpdates())
+            {
+                listView.SetObjects(new[] {
+                    new Model("first"),
+                    new Model("second")
+                });
+            }
+
+            Assert.IsTrue(listView.Frozen);
+            Assert.AreEqual(1, listView.GetItemCount());
+
+            listView.Unfreeze();
+
+            Assert.IsFalse(listView.Frozen);
+            Assert.AreEqual(2, listView.GetItemCount());
+        }
+
+        [TestMethod]
+        public void DeferViewUpdates_UnfreezesWhenScopeExitsThroughException()
+        {
+            using var listView = CreateListView();
+
+            try
+            {
+                using (listView.DeferViewUpdates())
+                {
+                    Assert.IsTrue(listView.Frozen);
+                    throw new TestException();
+                }
+            }
+            catch (TestException)
+            {
+            }
+
+            Assert.IsFalse(listView.Frozen);
+        }
+
+        [TestMethod]
+        public void DeferViewUpdates_ScopeDisposeIsIdempotent()
+        {
+            using var listView = CreateListView();
+            var scope = listView.DeferViewUpdates();
+
+            scope.Dispose();
+            Assert.IsFalse(listView.Frozen);
+
+            scope.Dispose();
+            Assert.IsFalse(listView.Frozen);
+        }
+
+        [TestMethod]
+        public void DeferViewUpdates_DisposingOwnerBeforeScopeDoesNotUnfreezeDisposedControl()
+        {
+            var listView = CreateListView();
+            var scope = listView.DeferViewUpdates();
+            Assert.IsTrue(listView.Frozen);
+
+            listView.Dispose();
+            scope.Dispose();
+
+            Assert.IsTrue(listView.IsDisposed);
+        }
+
+        [TestMethod]
+        public void DataListView_DeferViewUpdatesDefersDataSourceRefreshUntilScopeIsDisposed()
+        {
+            using var listView = CreateDataListView();
+            var rows = new BindingList<Model> { new Model("first") };
+            listView.DataSource = rows;
+            Assert.AreEqual(1, listView.GetItemCount());
+
+            using (listView.DeferViewUpdates())
+            {
+                rows.Add(new Model("second"));
+
+                Assert.IsTrue(listView.Frozen);
+                Assert.AreEqual(1, listView.GetItemCount());
+            }
+
+            Assert.IsFalse(listView.Frozen);
+            Assert.AreEqual(2, listView.GetItemCount());
+        }
+
+        [TestMethod]
+        public void FastDataListView_DeferViewUpdatesDefersDataSourceRefreshUntilScopeIsDisposed()
+        {
+            using var listView = CreateFastDataListView();
+            var rows = new BindingList<Model> { new Model("first") };
+            listView.DataSource = rows;
+            Assert.AreEqual(1, listView.GetItemCount());
+
+            using (listView.DeferViewUpdates())
+            {
+                rows.Add(new Model("second"));
+
+                Assert.IsTrue(listView.Frozen);
+                Assert.AreEqual(1, listView.GetItemCount());
+            }
+
+            Assert.IsFalse(listView.Frozen);
+            Assert.AreEqual(2, listView.GetItemCount());
+        }
+
+        private static ObjectListView CreateListView()
+        {
+            var listView = new ObjectListView();
+            listView.Columns.Add(new OLVColumn("Name", nameof(Model.Name)));
+            listView.CreateControl();
+            return listView;
+        }
+
+        private static DataListView CreateDataListView()
+        {
+            var listView = new DataListView
+            {
+                BindingContext = new BindingContext(),
+                AutoGenerateColumns = false
+            };
+            listView.Columns.Add(new OLVColumn("Name", nameof(Model.Name)));
+            listView.CreateControl();
+            return listView;
+        }
+
+        private static FastDataListView CreateFastDataListView()
+        {
+            var listView = new FastDataListView
+            {
+                BindingContext = new BindingContext(),
+                AutoGenerateColumns = false
+            };
+            listView.Columns.Add(new OLVColumn("Name", nameof(Model.Name)));
+            listView.CreateControl();
+            return listView;
+        }
+
+        private sealed class Model
+        {
+            public Model(string name)
+            {
+                Name = name;
+            }
+
+            public string Name { get; }
+        }
+
+        private sealed class TestException : System.Exception
+        {
+        }
+    }
+}

src/ObjectListView2022/ObjectListView.DeferredUpdates.cs

@@ -0,0 +1,45 @@
+using System;
+
+namespace BrightIdeasSoftware
+{
+    public partial class ObjectListView
+    {
+        /// <summary>
+        /// Freeze view updates until the returned scope is disposed.
+        /// </summary>
+        /// <remarks>
+        /// Scopes may be nested. The view is rebuilt when the outermost scope is disposed.
+        /// </remarks>
+        /// <returns>A scope that unfreezes the view when disposed.</returns>
+        public IDisposable DeferViewUpdates()
+        {
+            Freeze();
+            return new DeferredViewUpdateScope(this);
+        }
+
+        private sealed class DeferredViewUpdateScope : IDisposable
+        {
+            private ObjectListView owner;
+
+            public DeferredViewUpdateScope(ObjectListView owner)
+            {
+                this.owner = owner;
+            }
+
+            public void Dispose()
+            {
+                var listView = owner;
+                if (listView == null)
+                {
+                    return;
+                }
+
+                owner = null;
+                if (!listView.IsDisposed && !listView.Disposing)
+                {
+                    listView.Unfreeze();
+                }
+            }
+        }
+    }
+}