Unnullable.md

Unnullable

While working on a Blazor website, I found I had a situation where I wanted to bind properties to parameters (as one does in Blazor) but wanted to make it so that the value of the property can never be set to null. If a null value were to be passed, I wanted to ignore it and allow the property to retain its old value. (this was due to a complex page that handled a number of different routes, so some of the bound properties would only be bound to a real value for certain routes. so when navigating to some of the other routes, those properties would be set to null. I wanted to retain those values so that when navigating back the route values wouldn't be lost) This turned out to be a perfect use case for Someta:

[AttributeUsage(AttributeTargets.Property)]
public class UnnullableAttribute : Attribute, IPropertySetInterceptor
{
    public void SetPropertyValue(PropertyInfo propertyInfo, object instance, object oldValue, object newValue, Action<object> setter)
    {
        if (newValue != null)
            setter(newValue);
    }
}

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Usage:

public void UnnullableExample()
{
    var testClass = new TestClass();

    testClass.Value.ShouldBeNull();
    testClass.Value = "foo";
    testClass.Value.ShouldBe("foo");
    testClass.Value = null;
    testClass.Value.ShouldBe("foo");
}

public class TestClass
{
    [Unnullable]
    public string? Value { get; set; }
}

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