Merge pull request #5007 from workgroupengineering/fixes/Issue_5006

Fixes Issue 5006

src/Markup/Avalonia.Markup/Data/MultiBinding.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Data
         /// Gets or sets the binding priority.
         /// </summary>
         public BindingPriority Priority { get; set; }
-        
+
         /// <summary>
         /// Gets or sets the relative source for the binding.
         /// </summary>
@@ -77,12 +77,12 @@ namespace Avalonia.Data
             // We only respect `StringFormat` if the type of the property we're assigning to will
             // accept a string. Note that this is slightly different to WPF in that WPF only applies
             // `StringFormat` for target type `string` (not `object`).
-            if (!string.IsNullOrWhiteSpace(StringFormat) && 
+            if (!string.IsNullOrWhiteSpace(StringFormat) &&
                 (targetType == typeof(string) || targetType == typeof(object)))
             {
                 converter = new StringFormatMultiValueConverter(StringFormat, converter);
             }
-            
+
             var children = Bindings.Select(x => x.Initiate(target, null));
 
             var input = children.Select(x => x.Observable)
@@ -116,7 +116,16 @@ namespace Avalonia.Data
             }
 
             var culture = CultureInfo.CurrentCulture;
-            var converted = converter.Convert(values, targetType, ConverterParameter, culture);
+            values = new System.Collections.ObjectModel.ReadOnlyCollection<object>(values);
+            object converted;
+            if (converter != null)
+            {
+                converted = converter.Convert(values, targetType, ConverterParameter, culture);
+            }
+            else
+            {
+                converted = values;
+            }
 
             if (converted == null)
             {

tests/Avalonia.Markup.UnitTests/Data/MultiBindingTests.cs

@@ -157,6 +157,29 @@ namespace Avalonia.Markup.UnitTests.Data
             Assert.Equal("1,2,Fallback", target.Text);
         }
 
+        [Fact]
+        public void MultiBinding_Without_StringFormat_And_Converter()
+        {
+            var source = new { A = 1, B = 2, C = 3 };
+            var target = new ItemsControl {  };
+
+            var binding = new MultiBinding
+            {                
+                Bindings = new[]
+                {
+                    new Binding { Path = "A", Source = source },
+                    new Binding { Path = "B", Source = source },
+                    new Binding { Path = "C", Source = source },
+                },
+            };
+
+            target.Bind(ItemsControl.ItemsProperty, binding);
+            Assert.Equal(target.ItemCount, 3);
+            Assert.Equal(target.Items.ElementAt(0), source.A);
+            Assert.Equal(target.Items.ElementAt(1), source.B);
+            Assert.Equal(target.Items.ElementAt(2), source.C);
+        }
+
         private class ConcatConverter : IMultiValueConverter
         {
             public object Convert(IList<object> values, Type targetType, object parameter, CultureInfo culture)

tests/Avalonia.Markup.UnitTests/Extensions/IEnummerableExtension.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections;
+
+namespace Avalonia.Markup.UnitTests
+{
+   internal static class IEnumerableExtensions
+    {
+        public static object ElementAt(this IEnumerable source, int index)
+        {
+            var i = -1;
+            var enumerator = source.GetEnumerator();
+
+            while (enumerator.MoveNext() && ++i < index);
+            if (i == index)
+            {
+                return enumerator.Current;
+            }
+            throw new ArgumentOutOfRangeException(nameof(index));
+        }
+    }
+}