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c#validationenumstryparse
mweber
mweber

Reputation: 1302

Enum.TryParse returns true for any numeric values

I'm running into a behavior I wasn't expecting when using Enum.TryParse.

If I have an enum:

public enum MyEnum
{
  ValueA,
  ValueB,
  ValueC
}

And then I pass a numeric value (as a string) into Enum.TryParse, like:

MyEnum outputEnum;
bool result = Enum.TryParse("1234", out outputEnum);

Despite the string "1234" not being a possible value, result will come back as true, and my outputEnum will have a value of 1234.

Is there a way I can avoid this sort of behavior? I'm trying to write a function which will process arbitrary string input as an enum, and this has thrown a bit of a monkeywrench in my bad-input detection.

Upvotes: 73

Views: 19039

Answers (4)

user3656712
user3656712

Reputation: 1

as stated before, this is by design. If you want to avoid using Enum.IsDefined for performance purposes, then the hack is pretty simple:

Enum.TryParse("1234", out MyEnum outputEnum) && !int.TryParse(outputEnum.ToString(), out int shouldBeIgnored)

Upvotes: 0

Rob Streeting
Rob Streeting

Reputation: 1735

If you want to avoid numeric values being accepted entirely and want to avoid Enum.IsDefined(), you can add a check to the condition to verify that the string is not numeric. There's a bunch of different ways to do that with different trade-offs but, for example you could do this:

string valueToParse = "1234";
bool result = !valueToParse.All(char.IsDigit) && Enum.TryParse(valueToParse, out MyEnum outputEnum);

Upvotes: 1

Abbas Ghomi
Abbas Ghomi

Reputation: 159

Use it like this

bool result = Enum.TryParse("1234", out MyEnum outputEnum) && Enum.IsDefined(typeof(MyEnum), outputEnum);

The value of result will be false but the value of outputEnum is still 1234

Upvotes: 11

SLaks
SLaks

Reputation: 887275

This behavior is by design.

The documentation says:

. If value is the string representation of an integer that does not represent an underlying value of the TEnum enumeration, the method returns an enumeration member whose underlying value is value converted to an integral type. If this behavior is undesirable, call the IsDefined method to ensure that a particular string representation of an integer is actually a member of TEnum.

Call Enum.IsDefined to veryify that the value you parsed actually exists in this particular enum.

If you're dealing with [Flags] enums (bitmasks), it'll get more complicated.

Upvotes: 93

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