Develop Reference

C# lambda null runtime binding

I'm running into an odd scenario that doesn't happen on my PC, but does for a coworkers.
I have this piece of code:
LoaderHelpers.SetStringValue<blah>(this, "x", $"x response in Header",
() => jsonData.x.response[0].value, false);
The problem is that sometimes, "jsonData.x" is null and, for my coworker a 'cannot bind to null at runtime exception' is thrown, but not for me there isn't. I have code to handle the null scenario, but it's like his code never gets to that point and fails at the call level.
jsonData is of type dynamic.
The method code that handles the null scenario:
public static void SetStringValue<T>(IValidate data, string propertyName,
string valuePath, Func<string> value, bool required)
{
if (data.GetType().GetProperty(propertyName) != null)
{
try
{
if (string.IsNullOrEmpty(value()))
{
if (required)
data.DataValidationErrors.Add($"{valuePath} can't be empty");
data.GetType().GetProperty(propertyName).SetValue(data, null);
}
else
{
data.GetType().GetProperty(propertyName).SetValue(data, value());
}
}
catch
{
//property doesn't exist
if (required)
data.DataValidationErrors.Add($"{valuePath} doesn't exist");
data.GetType().GetProperty(propertyName).SetValue(data, null);
}
}
else
{
throw new NullReferenceException($"In {data.GetType()} => SetStringValue. " +
$"Passed property {propertyName}, but property doesn't exist.");
}
}
Again. Works perfect for me, but not for him. I'm completely lost. Maybe I don't understand how the lamba/function parameters work 100%, but I thought it only got evaluated when value() is invoked.
I should also mention that when I debug this code, I can step into the Nuget package and when he hits the same line, he can't. This maybe a useful hint.

If jsonData (or jsonData.x) is null (as it seems to be at this point) it will crash and give you that error every time you call the method value().
You need to check why jsonData.x is null. Maybe it´s a race condition caused by another thread setting this value to null, maybe it´s because a bad jsonData initialization... Can´t say since that code is not here.

There are so many things wrong with your code, i can't resist.
First of all, instead of copy/pasting the same stuff over and over, you might want to use a variable:
var property = data.GetType().GetProperty(propertyName);
Second, you pass a Func<string> and execute it multiple times, why is it even a function then? Yet again, better only evaluate it once and use a variable...
var unwrapped = value();
That would solve the issue, that Roberto Vázquez' answer adresses.
Then you are misusing NullReferenceException, instead rather use a ArgumentException
Next issue, that valuePath is only used in the exception message, that is a poor design to my beliefs.
The generic T parameter isnt even used, so get rid of it.
Last but not least, that catch-block doing the exact thing that could possibily throw the exception again, i cant see any reason why you would do this.
Finnaly this whole thing becomes a little more clear but its still a mess.
public static void SetStringValue(IValidate data, string propertyName,
string valuePath, Func<string> value, bool required)
{
if(data == null)
throw new ArgumentNullException(nameof(data));
var property = data.GetType().GetProperty(propertyName);
if(property == null)
throw new ArgumentException($"In {data.GetType()} => SetStringValue. " +
$"Passed property {propertyName}, but property doesn't exist.");
var unwrapped = value();
try
{
if (string.IsNullOrEmpty(unwrapped))
{
if (required)
data.DataValidationErrors.Add($"{valuePath} can't be empty");
unwrapped = null; // this might be unecessary.
}
property.SetValue(data, unwrapped);
}
catch(Exception e)
{
// This is probably a bad idea.
property.SetValue(data, null);
if (required)
data.DataValidationErrors.Add(Atleast put a better message here. e.Message ...);
}
}

Google Firebase Auth in Unity: How to read error codes

When using the Google Firebase Authentication plugin in Unity, how do you read error codes of faulted requests?
For example, within this code:
auth.SignInWithEmailAndPasswordAsync(email, password).ContinueWith(task => {
if(task.IsFaulted){
Debug.Log("ERROR ENCOUNTERED: " + task.Exception);
return;
}
if(task.IsCompleted){
// Success!
}
});
You can see that if an error occurs I can log the exception out, which prints the following:
ERROR ENCOUNTERED: System.AggregateException: Exception of type 'System.AggregateException' was thrown.
Firebase.FirebaseException: There is no user record corresponding to this identifier. The user may have been deleted.
That's very human-readable, but not very elegant to put into a switch statement. Is there any way for me to cast the task.Exception to be a FirebaseException so I can grab the error code? And is there a list of these error codes somewhere? I can find the documentation for the FirebaseException, but the error codes aren't there. Thanks for the help!
Edit:
So while I am still hoping for an answer, I've come to think that Google expects developers to use blanket error statements based on the context of the request. For example, when failing to sign in with an email and password (as in the above code), we should use the common statement of "Email or password is incorrect." The problem with that is that I can't let the user know the difference between them providing the incorrect details versus them entering an email which doesn't have an account associated with it at all.

Hopefully you've solved this by now but I've just come across the exact same problem and I'll share my solution:
According to MSDN, System.AggregateException is a representation of one or more errors that may occur during the task execution.
Therefore, you'll need to loop through the InnerException(s) presented by the AggregateException, and look for the suspected FirebaseException:
Retrieving the FirebaseException:
AggregateException ex = task.Exception as AggregateException;
if (ex != null) {
Firebase.FirebaseException fbEx = null;
foreach (Exception e in ex.InnerExceptions) {
fbEx = e as Firebase.FirebaseException;
if (fbEx != null)
break;
}
if (fbEx != null) {
Debug.LogError("Encountered a FirebaseException:" + fbEx.Message);
}
}
Getting the Error Code:
Wish I could help here but I haven't found anything - these aren't documented within the official API, AFIK. The only reference states: "If the error code is 0, the error is with the Task itself, and not the API. See the exception message for more detail."

I encountered the same dilemma trying to find out which error code I get from Firebase and display appropriate message for the user.
The correct way to read the Firebase Exception is with this function I created:
bool CheckError(AggregateException exception, int firebaseExceptionCode)
{
Firebase.FirebaseException fbEx = null;
foreach (Exception e in exception.Flatten().InnerExceptions)
{
fbEx = e as Firebase.FirebaseException;
if (fbEx != null)
break;
}
if (fbEx != null)
{
if (fbEx.ErrorCode == firebaseExceptionCode)
{
return true;
}
else
{
return false;
}
}
return false;
}
And you can use it like this:
auth.SignInWithEmailAndPasswordAsync("test#gmail.com", "password").ContinueWith(task => {
if (task.IsCanceled)
{
Debug.LogError("SignInWithEmailAndPasswordAsync was canceled.");
return;
}
if (task.IsFaulted)
{
if(CheckError(task.Exception, (int)Firebase.Auth.AuthError.EmailAlreadyInUse))
{
// do whatever you want in this case
Debug.LogError("Email already in use");
}
Debug.LogError("UpdateEmailAsync encountered an error: " + task.Exception);
}
}
Here is some more code samples from firebase:
https://github.com/firebase/quickstart-unity/blob/master/auth/testapp/Assets/Firebase/Sample/Auth/UIHandler.cs
I got the answer from this thread:
https://github.com/firebase/quickstart-unity/issues/96
I hope this will help someone. All the best!

Resharper states if/else condition will never be hit, why?

I have this code from a PushSharp example which details how to handle exceptions. For some reason all the else conditions are greyed out by Resharper, stating that The expression is always false. I don't see how this is possible.
// ex is an Exception passed in to the method
if (ex is NotificationException)
{
// Deal with the failed notification
var notification = ((NotificationException)ex).Notification;
var logItem = new PushLog($"{typePrefix} Notification failed", $"Notification Failed: {notification}");
_pushLogRepo.Insert(logItem);
}
else if (ex is DeviceSubscriptionExpiredException) // Resharper says this is always false
{
// exception handling code...
}
else if (ex is RetryAfterException) // Resharper says this is always false
{
// exception handling code...
}
else
{
Console.WriteLine("Notification Failed for some (Unknown Reason)");
}
Can someone explain how this is possible? I don't see how it can be. Here's a screenshot from VS2015 which is a bit clearer with syntax highlighting - ignore the error, I'm in the middle of refactoring.

This would happen if those classes inherit NotificationException, since then the first branch would always hit.

Throwing exceptions at multiple points (refactoring)

I'm writing a function that takes user input, runs a procedure in our database, and compares the values. Along the way, I need to check that we've received proper input and then that the query has returned an acceptable value.
private void DoTheThing(int? userInput1, int? userInput2, int valuePassedIn)
{
if (userInput1 == null || userInput2 == null)
{
Exception ex = new Exception();
ex.Data.Add("Message", "You screwed up.");
throw ex;
}
var queryResult = 0; //execute a query using the non-null inputs
if (queryResult == null) //or otherwise doesn't return an acceptable value
{
Exception ex = new Exception();
ex.Data.Add("Message", "some other thing happened");
throw ex;
}
else
{
//We're good, so do the thing
}
}
A quick note about this: I'm aware of the argument against exceptions as flow control and that I'd be better off checking the user's input before I even get this far. I won't get into all the details, but please accept that I'm kind of stuck writing the function this way.
That having been said, here's my question:
Given that the only differences between the 2 exceptions here is the message and the time at which they are thrown, how can I clean this code up to be both DRY and avoid running unnecessary code after determining that there will be a problem?
I thought about using a goto and placing the error code there, but that really only moves the problem around. If I move the exception code to the bottom and check for a message variable (or something similar), then I'm just running code that doesn't need to be run in the first place.

I suggest not throwing Exception (which means something went wrong, no comments are available), but ArgumentNullException and InvalidOperationException classes. Another amendment is avoding arrow-head
antipattern:
private void DoTheThing(int? userInput1, int? userInput2, int valuePassedIn)
{
// What actually went wrong? An argument "userInput1" is null
if (null == userInput1)
throw new ArgumentNullException("userInput1");
else if (null == userInput2)
throw new ArgumentNullException("userInput2"); // ...or userInput2 is null
var queryResult = executeSomeQuery(userInput1, userInput2, valuePassedIn);
// What went wrong? We don't expect that null can be returned;
// so the operation "executeSomeQuery" failed:
// we've provided validated (not null) values and got unexpected return.
// Let it have been known.
if (null == queryResult)
throw new InvalidOperationException(
String.Format("Query ({0}, {1}, {2}) returned null when bla-bla-bla expected",
userInput1, userInput2, valuePassedIn));
// We're good, so do the thing
// Note that's there's no "arrow-head antipattern":
// we're not within any "if" or "else" scope
}
Edit: Since every *Exception is inherited from Exception you can put some info into Data:
Exception ex = new ArgumentNullException("userInput1");
ex.Data.Add("Some key", "Some value");
throw ex;
but often Message is a far better place to explain what had heppened.

You might be better off creating a BadInputException class and a NullQueryResultException class. These do two different things and throwing a specific exception is better than throwing a generic Exception(...). In fact I think FXCop or Visual Studio's Code Analysis will give you a warning about throwing generic Exceptions.
It's not really all that much new code to write.
public class BadInputException : Exception
{
public BadInputException()
{
this.Data.Add("Message", "You screwed up.")
}
}
Then instead of this:
Exception ex = new Exception();
ex.Data.Add("Message", "You screwed up.");
throw ex;
Do this:
throw new BadInputException();
Edit: moved the "You screwed up" message from the Message property to the Data collection to match what the OP wants.

I would create a method:
private void CheckResult(bool cond, string msg, string info) {
if (!cond)
return;
Exception ex = new Exception();
ex.Data.Add(msg, info);
throw ex;
}
and call
CheckResult(userInput1 == null || userInput2 == null, "Message", "You screwed up.");
and
CheckResult(queryResult == null, "Message", "You screwed up.");

I think the QuestionRefactoring Guard Clauses is helpful for you .
There are something about this in Replace Nested Conditional with Guard Clauses.
Hope it's useful.

How to treat and test flow control if not with exceptions with c#?

What's the right way to treat and test flow control on methods that are void if not with exceptions? I've seen that Microsoft do not recomend such practice so what's the right way?
This is how how I'm treating parameters that shouldn't be accepted in my method:
public void RentOutCar(ReservationInfo reservationInfo)
{
try
{
if (string.IsNullOrEmpty(reservationInfo.ReservationNumber) || string.IsNullOrWhiteSpace(reservationInfo.ReservationNumber))
{
throw new ArgumentException("Reservation Number is null or empty.");
}
if (reservationInfo == null)
{
throw new ArgumentNullException("Null Reservation info.");
}
if (reservationInfo.Car == null)
{
throw new ArgumentNullException("No car registered to rent.");
}
if (reservationInfo.RentalDatetime == DateTime.MinValue || reservationInfo.RentalDatetime == DateTime.MaxValue)
{
throw new ArgumentException("Rental Date has an unreal value.");
}
if (reservationInfo.Car.Mileage <0)
{
throw new ArgumentOutOfRangeException("Mileage can't be less than 0.");
}
reserverationsRegister.ReservationsDone.Add(reservationInfo);
}
catch (Exception)
{
throw;
}
}

This is not what Microsoft mean when they say you should not control flow with exceptions.
While the use of exception handlers to catch errors and other events
that disrupt program execution is a good practice, the use of
exception handler as part of the regular program execution logic can
be expensive and should be avoided.
In other words, you should not throw (and subsequently catch) exceptions in situations where the code in the try block is likely to throw and represents legitimate program logic.
A contrived example of controlling flow with exceptions may look like:
int x = GetUserInput();
try
{
MustAcceptPositiveInput(x);
}
catch (InputIsNonPositiveException)
{
MustAcceptNonPositiveInput(x);
}
The equivalent 'correct' code may look like:
int x = GetUserInput();
if (x > 0)
{
MustAcceptPositiveInput(x);
}
else
{
MustAcceptNonPositiveInput(x);
}
Exceptions should be reserved for exceptional situations, those which are not part of expected program execution. It results in more readable, less surprising and more performant code.
What you are doing in your code is fine (except for the redundant try-catch and faulty order of tests as #Clay mentions), you are validating inputs for exceptional values, those which your code was not meant to handle.

Throwing an exception if the inputs are not valid is fine. Test reservationInfo for null first - or your other tests will break in unexpected ways. Also - no point in wrapping your tests in a try/catch if all you're going to do is rethrow it.
This is not a "control flow" issue as described in the article you put in the comments - and throwing exceptions is appropriate here.
You might consider wrapping just the "working code" in a try/catch, but only if you can recover from (or maybe log) any exceptions:
try
{
reserverationsRegister.ReservationsDone.Add(reservationInfo);
}
catch( Exception ex )
{
LogError( ex );
throw;
}