[Core] Fixes conversion binding a DateTime to a string if the locale is not the US

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue2049.cs

@@ -0,0 +1,122 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System;
+using System.Threading;
+using System.Globalization;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 2049, "Bound DateTimes Display in en-US Format Not Local Format", PlatformAffected.All)]
+	public class Issue2049 : TestContentPage
+	{
+		[Preserve(AllMembers = true)]
+		public class Model
+		{
+			public DateTime TheDate { get; set; }
+			public float FloatValue { get; set; }
+
+			decimal _decimal;
+			public decimal Decimal
+			{
+				get
+				{
+					return _decimal;
+				}
+				set
+				{
+					_decimal = value;
+					DecimalChange?.Invoke(value);
+				}
+			}
+
+			public static Action<decimal> DecimalChange;
+		}
+
+		DateTime testDate = DateTime.ParseExact("2077-12-31T13:55:56", "yyyy-MM-ddTHH:mm:ss", CultureInfo.InvariantCulture);
+		int _localeIndex = 0;
+		string[] _localeIds = new[] { "en-US", "ru-RU", "en-AU", "zh-Hans" };
+		string _instuctions = $"When you change the locale, the date format must change.{Environment.NewLine}Current locale: ";
+		Label descLabel = new Label();
+		Label decimalResult = new Label();
+
+		protected override void Init()
+		{
+			UpdateContext();
+
+			var label = new Label();
+			label.SetBinding(Label.TextProperty, nameof(Model.TheDate));
+			var labelFloat = new Label();
+			labelFloat.SetBinding(Label.TextProperty, nameof(Model.Decimal));
+			var entry = new Entry
+			{
+				Keyboard = Keyboard.Numeric
+			};
+			entry.SetBinding(Entry.TextProperty, nameof(Model.Decimal));
+			Model.DecimalChange = (v) => {
+				decimalResult.Text = v.ToString(CultureInfo.CurrentCulture);
+			};
+
+			UpdateDescLabel();
+
+			var layout = new StackLayout
+			{
+				Children = {
+					descLabel,
+					new Button()
+					{
+						Text = "Change Locale",
+						Command = new Command(() => ChangeLocale())
+					},
+					label,
+					labelFloat,
+					entry,
+					decimalResult
+				}
+			};
+
+			Content = layout;
+		}
+
+		void UpdateContext()
+		{
+			BindingContext = new Model
+			{
+				TheDate = DateTime.ParseExact("2077-12-31T13:55:56", "yyyy-MM-ddTHH:mm:ss", CultureInfo.InvariantCulture),
+				FloatValue = 123.456f, // in some locales, the decimal symbol may not be a dot.
+				Decimal = 456.789m
+			};
+		}
+
+		void ChangeLocale()
+		{
+			if (++_localeIndex > _localeIds.Length - 1)
+				_localeIndex = 0;
+			var locale = _localeIds[_localeIndex];
+
+			Thread.CurrentThread.CurrentCulture = new CultureInfo(locale);
+			UpdateDescLabel();
+			UpdateContext();
+		}
+
+		void UpdateDescLabel() => descLabel.Text = $"{_instuctions}{Thread.CurrentThread.CurrentCulture.DisplayName}";
+
+#if UITEST
+		[Test]
+		public void Issue2049Test ()
+		{
+			foreach (var locale in _localeIds)
+			{
+				if (RunningApp.Query(query => query.Text(testDate.ToString(new CultureInfo(locale)))).Length != 1)
+					Assert.Fail();
+				RunningApp.Tap("Change Locale");
+			}
+		} 
+#endif
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -90,6 +90,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla36014.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla36649.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla36559.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue2049.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla36171.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla36780.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla36651.cs" />
@@ -967,4 +968,4 @@
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
   </ItemGroup>
-</Project>
+</Project>

Xamarin.Forms.Core/BindableProperty.cs

@@ -51,7 +51,8 @@ public sealed class BindableProperty
 			{ typeof(long), new[] { typeof(string), typeof(float), typeof(double), typeof(decimal) } },
 			{ typeof(char), new[] { typeof(string), typeof(ushort), typeof(int), typeof(uint), typeof(long), typeof(ulong), typeof(float), typeof(double), typeof(decimal) } },
 			{ typeof(float), new[] { typeof(string), typeof(double) } },
-			{ typeof(ulong), new[] { typeof(string), typeof(float), typeof(double), typeof(decimal) } }
+			{ typeof(ulong), new[] { typeof(string), typeof(float), typeof(double), typeof(decimal) } },
+			{ typeof(DateTime), new[] { typeof(string) } }
 		};
 
 		BindableProperty(string propertyName, Type returnType, Type declaringType, object defaultValue, BindingMode defaultBindingMode = BindingMode.OneWay,
@@ -317,7 +318,7 @@ internal bool TryConvert(ref object value)
 			TypeConverter typeConverterTo;
 			if (SimpleConvertTypes.TryGetValue(valueType, out convertableTo) && Array.IndexOf(convertableTo, type) != -1)
 			{
-				value = Convert.ChangeType(value, type);
+				value = Convert.ChangeType(value, type, System.Globalization.CultureInfo.CurrentCulture);
 			}
 			else if (WellKnownConvertTypes.TryGetValue(type, out typeConverterTo) && typeConverterTo.CanConvertFrom(valueType))
 			{

Xamarin.Forms.Core/BindingExpression.cs

@@ -423,19 +423,26 @@ bool TryConvert(BindingExpressionPart part, ref object value, Type convertTo, bo
 				return true;
 
 			object original = value;
+			var locale = CultureInfo.InvariantCulture;
 			try
 			{
 				var stringValue = value as string ?? string.Empty;
-				// see: https://bugzilla.xamarin.com/show_bug.cgi?id=32871
-				// do not canonicalize "*.[.]"; "1." should not update bound BindableProperty
-				if (stringValue.EndsWith(".") && DecimalTypes.Contains(convertTo))
-					throw new FormatException();
 
-				// do not canonicalize "-0"; user will likely enter a period after "-0"
-				if (stringValue == "-0" && DecimalTypes.Contains(convertTo))
-					throw new FormatException();
+				if (DecimalTypes.Contains(convertTo))
+				{
+					// see: https://bugzilla.xamarin.com/show_bug.cgi?id=32871
+					// do not canonicalize "*.[.]"; "1." should not update bound BindableProperty
+					if (stringValue.EndsWith("."))
+						throw new FormatException();
+
+					// do not canonicalize "-0"; user will likely enter a period after "-0"
+					if (stringValue == "-0")
+						throw new FormatException();
+
+					locale = CultureInfo.CurrentCulture;
+				}
 
-				value = Convert.ChangeType(value, convertTo, CultureInfo.InvariantCulture);
+				value = Convert.ChangeType(value, convertTo, locale);
 				return true;
 			}
 			catch (InvalidCastException)