Support default value for value types in BindableProperty (xamarin#2827)

* Support default value for value types in BindableProperty when no explicit default is provided * Add unit test for enum/struct BindableProperty default values
sttassociates · May 29, 2018 · 6d74745 · 6d74745
1 parent 7cab837
commit 6d74745
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Showing 2 changed files with 65 additions and 1 deletion.
diff --git a/Xamarin.Forms.Core.UnitTests/BindablePropertyUnitTests.cs b/Xamarin.Forms.Core.UnitTests/BindablePropertyUnitTests.cs
@@ -131,5 +131,66 @@ public void NullableProperty ()
 			bindable.SetValue (prop, null);
 			Assert.AreEqual (null, bindable.GetValue (prop));
 		}
+
+		[Test]
+		public void ValueTypePropertyDefaultValue ()
+		{
+			// Create BindableProperty without explicit default value
+			var prop = BindableProperty.Create ("foo", typeof(int), typeof(MockBindable));
+			Assert.AreEqual (typeof(int), prop.ReturnType);
+
+			Assert.AreEqual(prop.DefaultValue, 0);
+
+			var bindable = new MockBindable ();
+			Assert.AreEqual (0, bindable.GetValue (prop));
+
+			bindable.SetValue (prop, 1);
+			Assert.AreEqual (1, bindable.GetValue (prop));
+		}
+
+		enum TestEnum
+		{
+			One,Two,Three
+		}
+
+		[Test]
+		public void EnumPropertyDefaultValue ()
+		{
+			// Create BindableProperty without explicit default value
+			var prop = BindableProperty.Create ("foo", typeof(TestEnum), typeof(MockBindable));
+			Assert.AreEqual (typeof(TestEnum), prop.ReturnType);
+
+			Assert.AreEqual(prop.DefaultValue, default(TestEnum));
+
+			var bindable = new MockBindable ();
+			Assert.AreEqual (default(TestEnum), bindable.GetValue (prop));
+
+			bindable.SetValue (prop, TestEnum.Two);
+			Assert.AreEqual (TestEnum.Two, bindable.GetValue (prop));
+		}
+
+		struct TestStruct
+		{
+			public int IntValue;
+		}
+
+		[Test]
+		public void StructPropertyDefaultValue ()
+		{
+			// Create BindableProperty without explicit default value
+			var prop = BindableProperty.Create ("foo", typeof(TestStruct), typeof(MockBindable));
+			Assert.AreEqual (typeof(TestStruct), prop.ReturnType);
+
+			Assert.AreEqual(((TestStruct)prop.DefaultValue).IntValue, default(int));
+
+			var bindable = new MockBindable ();
+			Assert.AreEqual (default(int), ((TestStruct)bindable.GetValue (prop)).IntValue);
+
+			var propStruct = new TestStruct {IntValue = 1};
+
+			bindable.SetValue (prop, propStruct);
+			Assert.AreEqual (1, ((TestStruct)bindable.GetValue (prop)).IntValue);
+		}
+
 	}
 }
diff --git a/Xamarin.Forms.Core/BindableProperty.cs b/Xamarin.Forms.Core/BindableProperty.cs
@@ -68,10 +68,13 @@ public sealed class BindableProperty
 			// don't use Enum.IsDefined as its redonkulously expensive for what it does
 			if (defaultBindingMode != BindingMode.Default && defaultBindingMode != BindingMode.OneWay && defaultBindingMode != BindingMode.OneWayToSource && defaultBindingMode != BindingMode.TwoWay && defaultBindingMode != BindingMode.OneTime)
 				throw new ArgumentException("Not a valid type of BindingMode", "defaultBindingMode");
+
 			if (defaultValue == null && Nullable.GetUnderlyingType(returnType) == null && returnType.GetTypeInfo().IsValueType)
-				throw new ArgumentException("Not a valid default value", "defaultValue");
+				defaultValue = Activator.CreateInstance(returnType);
+
 			if (defaultValue != null && !returnType.IsInstanceOfType(defaultValue))
 				throw new ArgumentException("Default value did not match return type", "defaultValue");
+
 			if (defaultBindingMode == BindingMode.Default)
 				defaultBindingMode = BindingMode.OneWay;