MVVM Light binding framework for Xamarin also supports FallbackValue and TargetNullValue

gistfile1.txt

[Test]
public void BindingDeepPath_DeepSourceExistingPathGraduallySettingPath_NoError()
{
    VmSource = new TestViewModel();
    VmTarget = new TestViewModel();

    const string fallback = "This is the fallback";
    const string targetNull = "Target is null";

    var binding = new Helpers.Binding<string, string>(
        VmSource,
        () => VmSource.Nested.Nested.Model.MyProperty,
        VmTarget,
        () => VmTarget.TargetProperty,
        fallbackValue: fallback,
        targetNullValue: targetNull);

    Assert.AreEqual(fallback, VmTarget.TargetProperty);
    VmSource.Nested = new TestViewModel();
    Assert.AreEqual(fallback, VmTarget.TargetProperty);
    VmSource.Nested.Nested = new TestViewModel();
    Assert.AreEqual(fallback, VmTarget.TargetProperty);
    VmSource.Nested.Nested.Model = new TestModel();
    Assert.AreEqual(targetNull, VmTarget.TargetProperty);
    var initialValue = "Initial value";
    VmSource.Nested.Nested.Model.MyProperty = initialValue;
    Assert.AreEqual(initialValue, VmTarget.TargetProperty);
    var newValue = DateTime.Now.Ticks.ToString();
    VmSource.Nested.Nested.Model.MyProperty = newValue;
    Assert.AreEqual(newValue, VmTarget.TargetProperty);
}