Fixes bug for being unable to have multiple datalabels in same series (#1489)

Author: OssianEPPlus

src/EPPlus/Drawing/Chart/ExcelChartDataLabelCollection.cs

@@ -52,13 +52,12 @@ public ExcelChartDataLabelItem Add(int index)
                 {
                     throw (new ArgumentException($"Data label with index {index} already exists"));
                 }
-                return CreateDataLabel(ix);
+                return CreateDataLabel(index);
             }
         }
 
         private ExcelChartDataLabelItem CreateDataLabel(int idx)
         {
-            var pos = GetItemAfter(idx);
             XmlElement element = CreateElement(idx);
             var dl = new ExcelChartDataLabelItem(_chart, NameSpaceManager, element, "dLbl", SchemaNodeOrder) { Index=idx };
 
@@ -80,11 +79,11 @@ private XmlElement CreateElement(int idx)
             if (idx < _list.Count)
             {
                 pointNode = TopNode.OwnerDocument.CreateElement("c", "dLbl", ExcelPackage.schemaMain);
-                _list[idx].TopNode.InsertBefore(pointNode, _list[idx].TopNode);
+                TopNode.InsertBefore(pointNode, _list[idx].TopNode);
             }
             else
             {
-                pointNode = (XmlElement)CreateNode("c:dLbl");
+                pointNode = (XmlElement)CreateNode("c:dLbl", false, true);
             }
             return pointNode;
         }

src/EPPlusTest/Drawing/Chart/DatalabelTest.cs

@@ -2,6 +2,7 @@
 using OfficeOpenXml;
 using OfficeOpenXml.Drawing.Chart;
 using System;
+using System.Drawing;
 
 namespace EPPlusTest.Drawing.Chart
 {
@@ -293,5 +294,34 @@ void AdjustDataLabelItem(ref ExcelChartDataLabelItem label)
 
             label.Layout.ManualLayout.Left = -30;
         }
+
+        [TestMethod]
+        public void TwoLabelsOnSameSeries()
+        {
+            using (var pck = OpenPackage("ColumnChartStuffEasy.xlsx", true))
+            {
+                var cSheet = pck.Workbook.Worksheets.Add("ColumnChartSheet");
+
+                var range = cSheet.Cells["A1:C3"];
+                var table = cSheet.Tables.Add(range, "DataTable");
+                table.ShowHeader = false;
+
+                range.Formula = "ROW() + COLUMN()";
+
+                cSheet.Calculate();
+
+                var sChart = cSheet.Drawings.AddBarChart("simpleChart", eBarChartType.ColumnStacked);
+
+                sChart.Series.Add(cSheet.Cells["A1:A3"]);
+                sChart.Series.Add(cSheet.Cells["B1:B3"]);
+                sChart.Series.Add(cSheet.Cells["C1:C3"]);
+
+                sChart.Series[2].DataLabel.DataLabels.Add(0);
+                sChart.Series[2].DataLabel.DataLabels.Add(2);
+                sChart.Series[2].DataLabel.DataLabels.Add(1);
+
+                SaveAndCleanup(pck);
+            }
+        }
     }
 }