C# 通过反射获取属性值没有默认值

Question

I have this code:

messageDto = new CorrelationDto()
{
timestamp = default,
};

var isDefault = messageDto.GetType().GetProperty("timestamp").GetValue(messageDto) == default; // FALSE
var isDefault2 = messageDto.timestamp == default; // TRUE

where timestamp is a DateTime.

As you can see, getting the value through reflection and comparing to default return false. Do you have any idea why it's happening and how should I do to check for default values? Thanks

== EDIT ==

It has been pointed to me that the return value of GetValue() is an object and so it must be casted to DateTime in order for the default to work. Unfortunately I cannot because I'm running this test on all the properties of an object to discover if this object is initialized or not (so I check for null or default value). And the messageDto in reality is a generic type so I don't know the types of its properties a priori.

Answer 1

GetValue returns an object of type object , because it can't know at compile time what the type of the property is. The default value of an object is null , but since DateTime is a value type, its default value cannot be null .

Cast the result of GetValue to DateTime .

Answer 2

If I correctly understood you, this is how I solved this problem:

    private static bool IsValueNumericDefault(object value)
    {
        var intVal = 1;
        var doubleVal = 1.0;

        return (int.TryParse($"{value}", out intVal) || double.TryParse($"{value}", out doubleVal)) && 
               (intVal == default || doubleVal == default);
    }

I check random object value through casting it to string and try parse to type that I check. Value parameter is returned by reflection method.GetValue(). You can try to parse it to DateTime or any other type that you check.