Checking whether an enum value exists by a parse test in C#

Say you have the following ShipmentOption enumeration:

public enum ShipmentOption
{
	Land,
	Sea,
	Air
}

By default each enumeration value will have an integer representation starting with 0. So 0 corresponds to Land, 1 to Sea and 2 to Air. In addition, each enumeration entry can be stringified such as “Land”, “Sea” and “Air”.

The Enum class has a TryParse method that helps you convert the string representation of the enumeration into the actual enumeration value.

Here’s an example of converting a string into an enum:

public void SendShipment(string shipmentType)
{
	ShipmentOption shipmentOption;
	if (Enum.TryParse<ShipmentOption>(Convert.ToString(shipmentType), true, out shipmentOption))
	{
		Console.WriteLine("This type is defined: {0}", shipmentOption);
	}
	else
	{
		throw new InvalidEnumArgumentException(string.Format("Enum value {0} doesn't exist.", shipmentType));
	}
}

The InvalidEnumArgumentException class is defined in the System.ComponentModel namespace.

The “true” in the TryParse function means that the check is case-insensitive, so even “air” or “land” are valid inputs.

Calling the function like…

SendShipment("air");

…will output the following:

This type is defined: Air

“mickeymouse” on the other hand will throw an exception:

Enum value mickeymouse doesn’t exist.

Note that the TryParse function can also be called with a stringified integer, as follows:

public void SendShipment(int numericShipmentType)
{
	ShipmentOption shipmentOption;
	if (Enum.TryParse<ShipmentOption>(Convert.ToString(numericShipmentType), out shipmentOption))
	{
		Console.WriteLine("This type is defined: {0}", (ShipmentOption)numericShipmentType);
	}
	else
	{
		throw new InvalidEnumArgumentException("ShipmentOption", numericShipmentType, typeof(ShipmentOption));
	}
}

However, TryParse will always return true in that case. If the integer can not be converted into a matching enumeration value then the enumeration will take on the integer value instead.

Example with a valid integer:

SendShipment(0);

This type is defined: Land

Example with an invalid integer:

SendShipment(8);

This type is defined: 8

View all various C# language feature related posts here.