Clash Royale CLAN TAG#URR8PPP

Get the type from a nullable variable

public class MyType

public int? MyId get; set;


MyType myType = new MyType();
myType.MyId.GetType()


the last line returns an exception since MyId is not set (ie. it's null). How I get the type (int? or even int) in this case? Note, int? is used as an example, the variable may have any type, this is just a simplified example.

MyId

int?

int

int?

Note, according to Microsoft, this is supposed to work:

int? a = 17;
Type typeOfA = a.GetType();
Console.WriteLine(typeOfA.FullName);
// Output:
// System.Int32


and it does work when the value is assigned...

EDIT.

Looking at some of the replies and comments, I would like to add that in code, I pass myType.MyId as an object to a method that needs to figure out its type. Basically it looks similar to:

public void RunQuery(string sql, List<(string parameterName, object parameterValue)> parameters)


so myType.MyId is passed into RunQuery as parameterValue

GetType()

typeof(MyType).GetProperty("MyId").PropertyType

Nullable<int>

Nullable.GetUnderlyingType(type)

2 Answers
2

You can use reflection to get declared type of a property (which is known at compile time):

Type t = typeof(MyType).GetProperty(nameof(MyType.MyId)).PropertyType;


And GetType() is used to figure out the actual type of an object in runtime, but that does not make sense for a null reference.

GetType()

null

Edit:

When you cast Nullable<T> to an Object, its value is boxed, so, if it was null, you will get just an Object variable with null reference, and you won't be able to find out the type any more.

Nullable<T>

Object

null

Object

null

So, you should somehow change your infrastructure to make the type be passed with your parameter. The fastest workaround is to pass it explicitly

List<(string parameterName, object parameterValue, Type parameterType)> parameters


Check out System.Data.SqlClient.SqlParameter, I am not sure, but this is probably exactly what you need to use.

object

Method<T>(T parameterValue)

Type type = typeof (T);

[Edited], I've re-written my solution to address your question: Making a function that is agnostic to MyType:

string GetPropertyName<T>(T prop)

var type = typeof(T);
if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))

return type.GenericTypeArguments[0].FullName;

else

return type.FullName;




You can now call it like this:

MyType myType = new MyType();
string name = GetPropertyName(myType.MyId);
Console.WriteLine(name); // Outputs System.Int32


I've test it, and it's working for me.

BTW, if you pass it a non-nullable member, it will return that property name. You can test that for yourself.

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