Fixes line series gaps

src/LiveChartsCore/Measure/VectorManager.cs

@@ -20,8 +20,6 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-using System;
-using System.Collections.Generic;
 using LiveChartsCore.Drawing.Segments;
 
 namespace LiveChartsCore.Measure;
@@ -35,6 +33,13 @@ public void AddConsecutiveSegment(Segment segment, bool followsPrevious)
         LinkedListNode<Segment>? replaceCandidate = null;
         List<LinkedListNode<Segment>>? deleteCandidates = null;
 
+        if (_currentNode is not null && segment.Id < _currentNode.Value.Id)
+        {
+            // this is a special case, normally caused because the gaps changed (null points).
+            // restart from the beginning to keep the linked list in sync.
+            _currentNode = list.First;
+        }
+
         // look for the segment in the list
         while (_currentNode is not null && _currentNode.Value != segment)
         {
@@ -64,14 +69,15 @@ public void AddConsecutiveSegment(Segment segment, bool followsPrevious)
                 // at this point we know that the path contains this segment
                 // but the instance changed, so we replace the node
 
-                if (replaceCandidate is null)
-                    throw new InvalidOperationException("This should not happen :(");
+                if (replaceCandidate is not null)
+                {
+                    if (followsPrevious)
+                        segment.Copy(replaceCandidate.Value);
 
-                if (followsPrevious)
-                    segment.Copy(replaceCandidate.Value);
+                    replaceCandidate.Value = segment;
+                }
 
-                replaceCandidate.Value = segment;
-                _currentNode = replaceCandidate.Next;
+                _currentNode = replaceCandidate?.Next;
             }
             else
             {

tests/SnapshotTests/LineSeriesTests.cs

@@ -1,4 +1,4 @@
-using LiveChartsCore.Defaults;
+using System.Collections.ObjectModel;
 using LiveChartsCore.SkiaSharpView;
 using LiveChartsCore.SkiaSharpView.Painting;
 using LiveChartsCore.SkiaSharpView.SKCharts;
@@ -85,4 +85,262 @@ public void Curved()
 
         chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(Curved)}");
     }
+
+    [TestMethod]
+    public void VectorOperationsRemoveEnd()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+
+        // draw the chart
+        _ = chart.GetImage();
+
+        // do the change, redraw and assert
+        values.RemoveAt(values.Count - 1);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsRemoveEnd)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsRemoveStart()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+        // draw the chart
+        _ = chart.GetImage();
+        // do the change, redraw and assert
+        values.RemoveAt(0);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsRemoveStart)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsRemoveMiddle()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+        // draw the chart
+        _ = chart.GetImage();
+
+        // do the change, redraw and assert
+        values.RemoveAt(2);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsRemoveMiddle)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsAdd()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+        // draw the chart
+        _ = chart.GetImage();
+
+        // do the change, redraw and assert
+        values.Add(6);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsAdd)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsInsertMiddle()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+
+        // draw the chart
+        _ = chart.GetImage();
+
+        // do the change, redraw and assert
+        values.Insert(2, 6);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsInsertMiddle)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsInsertStart()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+        // draw the chart
+        _ = chart.GetImage();
+        // do the change, redraw and assert
+        values.Insert(0, 6);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsInsertStart)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsInsertEnd()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+        // draw the chart
+        _ = chart.GetImage();
+        // do the change, redraw and assert
+        values.Insert(values.Count, 6);
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsInsertEnd)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsReplace()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+
+        // draw the chart
+        _ = chart.GetImage();
+
+        // do the change, redraw and assert
+        values[2] = 6;
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsReplace)}");
+    }
+
+    [TestMethod]
+    public void VectorOperationsClear()
+    {
+        var values = new ObservableCollection<int>([1, 2, 3, 4, 5]);
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int>
+                {
+                    Values = values,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+        // draw the chart
+        _ = chart.GetImage();
+        // do the change, redraw and assert
+        values.Clear();
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(VectorOperationsClear)}");
+    }
+
+
+    [TestMethod]
+    public void Gaps()
+    {
+        var points = new ObservableCollection<int?>([1, 1]);
+
+        var chart = new SKCartesianChart
+        {
+            Series = [
+                new LineSeries<int?>
+                {
+                    Values = points,
+                    Fill = null
+                }
+            ],
+            Width = 600,
+            Height = 600
+        };
+
+        _ = chart.GetImage();
+
+        var count = 0;
+        int?[] toAdd = [null, 1];
+
+        void Push()
+        {
+            points.Add(toAdd[count++ % toAdd.Length]);
+            points.RemoveAt(0);
+
+            _ = chart.GetImage();
+        }
+
+        Push();
+        Push();
+        Push();
+        Push();
+
+        chart.AssertSnapshotMatches($"{nameof(LineSeriesTests)}_{nameof(Gaps)}");
+    }
 }