I am fully aware that what I am about to ask is not good practice... but:
Let's say I have a class containing a function that I want to always return a value, but store any exceptions that might occur for later processing. Something Like:
public Exception _error { get; set; }
public bool IsValid()
{
try
{
//do something here to cause exception
return true;
}
catch (Exception ex)
{
_error = ex;
return false;
}
}
Now that I have stored the exception, is it at all possible to throw the exception from an outside method while maintaining both the original stack trace and exception type?
throw _error; //lose stack trace
throw new Exception("", _error) //lose type
Thanks for looking or answering.
EDIT:
Thanks to some additional points, I realize that the below idea only takes away information and doesn't really add or simplify the situation. Thanks again to everyone.
After pondering Pieter's answer and comments, I'm now wondering if making a wrapper Exception class like the below could be a partial solution. This overrides as much of the exception as possible to make the New exception look like its innerexception, including the stacktrace.. dirty I know, but interesting:
public class ExceptionWrapper : Exception
{
private Exception _innerException;
public ExceptionWrapper(Exception ex) : base("", ex)
{
_innerException = ex;
this.Source = ex.Source;
this.HelpLink = ex.HelpLink;
}
public override string StackTrace
{
get
{
return _innerException.StackTrace;
}
}
public override System.Collections.IDictionary Data
{
get
{
return _innerException.Data;
}
}
public override string Message
{
get
{
return _innerException.Message;
}
}
public new Exception InnerException
{
get
{
return _innerException.InnerException;
}
}
}
No, this is not possible.
However, you normally solve this is by wrapping the exception in a new exception:
throw new MyException("Wrapper", _error);
This does maintain the stack trace of _error, but you do get a new exception. Your solution in your second example is the correct way of handling these cases.
Consider using reflection to create a wrapper exception of the correct type (Activator.CreateInstance) and calling the constructor that will accept the inner exception you have stored.
For example:
[Test]
public void test()
{
Exception ex = new ArgumentNullException();
Exception wrapped = (Exception)Activator.
CreateInstance(ex.GetType(), "wrapped", ex);
Type expectedType = typeof(ArgumentNullException);
Assert.IsInstanceOf(expectedType, wrapped, "Is ArgumentNullException.");
Assert.AreEqual(ex, wrapped.InnerException, "Exception is wrapped.");
}
Update
In order to mitigate the constructor issue, you could consider using the default constructor (should be there for an exception that follows design guidelines, but not mandatory) and then patching up the new instance by setting its fields via reflection.
I agree the approach is highly "meh" it's more an exploration of an idea. I wouldn't recommend it.
The exception design guidelines require a default constructor, so this sort of behaviour may go on in the framework somewhere anyway. Perhaps for some sort of icky serialization\deserialization of exceptions across some sort of communications boundary?
It seems that .net-4.5 added a new API for capturing stack/info about exceptions and rethrowing them in different contexts. This is called ExceptionDispatchInfo. It is useful if you find yourself needing more control over running tasks indirectly, like if you do manual thread management for jobs or Task does not exactly fit your needs. In your example, it should look like this:
public ExceptionDispatchInfo _error { get; private set; }
public bool IsValid()
{
try
{
//do something here to cause exception
return true;
}
catch (Exception ex)
{
_error = ExceptionDispatchInfo.Capture(ex);
return false;
}
}
/// <summary>Throw underlying exception if invalid.</summary>
public void AssertWasValid() => _error?.Throw();
Now, it doesn’t preserve the original caller. The displayed stack trace shows the calls from the original try block into the code in there, a statement breaking the original and new parts of the stack, and then the calls into ExceptionDispatchInfo.Throw() itself as the new part of the shown stack. This seems similar to how traces with async code look. If you care about the original caller, seems this won’t work. But if you care about getting the line/method that threw the exception, this should be sufficient.
Related
Here What I want to do, but do not know if it will work or if there is a better way:
if (condition1){
try {
Block1;
}
} else if (condition2){
try {
Block2;
}
}
catch(ExceptionType1 ex) { process;}
catch(ExceptionType2 ex) { process;}
catch(Exception) {throw;}
So is that the best way this could be done?
This can do what you want.
try {
if (condition1) {
Block1;
} else if (condition2) {
Block2;
}
}
catch(ExceptionType1 ex) { process;}
catch(ExceptionType2 ex) { process;}
catch(Exception) {throw;}
If not, try to put a clear detailed example.
There is no syntax to support exactly, but you might be able to get a similar effect by defining exception classes, and purposely throwing those exceptions in block1 and block2, either through separate try/catches or if/conditonal statements (checking for null, "", etc.)
Here's an example of an exception class behind defined, taken from here
[Serializable()]
public class InvalidDepartmentException : System.Exception
{
public InvalidDepartmentException() : base() { }
public InvalidDepartmentException(string message) : base(message) { }
public InvalidDepartmentException(string message, System.Exception inner) : base(message, inner) { }
// A constructor is needed for serialization when an
// exception propagates from a remoting server to the client.
protected InvalidDepartmentException(System.Runtime.Serialization.SerializationInfo info,
System.Runtime.Serialization.StreamingContext context) : base(info, context) { }
}
In the logic that you want to throw the exceptions in, you just need to define and throw the Exception class you defined. This can be done in a separate catch block, as well
System.ArgumentException argEx = new System.ArgumentException("Index is out of range", "index", ex);
throw argEx;
I'm not sure what you try to achieve with your structure in detail. But I see currently no issue in wrapping the whole statement block into a single try-block #AbdelAzizAbdelLatef mentioned and catch different exception types.
Maybe you can think about, to move your both code blocks (Block1 & Block2) into own functions/methods and perform a specific exception handling there and maybe returning some status code from each new block function. This would be a more clean code approach.
I am writing a HttpHandler and as part of my internal design, I throw different exceptions and catch them at the top level in order to determine what status code to set the request to.
I.e.
ArgumentException triggers Bad Request
AuthenticationException triggers Unauthorised
OracleException triggers InternalServerError
etc
The problem I've found is that I was using InvalidOperationException to trigger NotFound, but a bug in my code caused me to realise that, of course, some system exceptions inherit from these base system exceptions, which causes unexpected responses.
I.e. I found that ObjectDisposedException inherits from InvalidOperationException, which means that the response returns a 404 instead of 500.
Is there a way to catch just the base exception?
I found this thread which suggests I could do a filter and rethrow, but that seems hacky.
Would I be better off just creating my own exception types to save all this hassle?
If you only want to pass the HTTP result code (and maybe error message line) to the client, then I recommend you create a single custom exception:
public class MyCustomException : Exception { // Or maybe InvalidOperationException
public int StatusCode {get;set;}
public string Status {get;set;}
}
etc.
As far as I am aware there's no way to catch an exception but not catch inherited exceptions. The problem is that you're considering the base exception to be more specific than the inherited exception, which is the opposite of how they're intended to work (Inherited exceptions should be more specific subsets of their parent, so conceptually if you can handle the parent you should be able to handle the inherited exception).
Your options basically are:
Create your own exception type & only catch this. If your exception falls under the definition of an InvalidOperationException then you can inherit from this. Then you can catch yours specifically.
Catch, inspect, and re-throw if it's not what you're after. This technique I typically try to avoid but is sometimes required if exception types are too generic. e.g.
catch (InvalidOperationException ex) {
if (ex.GetType() != typeof(InvalidOperationException)) throw;
/* Do stuff */
}
It is not possible to only catch base exceptions.
In this case it is best to create a custom exception, rather than use the system's exception types.
public class HttpErrorException : Exception
{
public HttpStatusCode StatusCode { get; private set; }
public HttpErrorException(HttpStatusCode code, string message)
: base(message)
{
this.StatusCode = code;
}
}
throw new HttpErrorException(400, "You sent a bad request!");
If the original intention was to obfuscate the HTTP status codes, and instead use their text names, factory methods can be created.
public class HttpErrorException : Exception
{
public HttpStatusCode StatusCode { get; private set; }
private HttpErrorException(HttpStatusCode code, string message)
: base(message)
{
this.StatusCode = code;
}
public static HttpErrorException BadRequest(string message)
{
return new HttpErrorException(400, message);
}
public static HttpErrorException InternalServerError(string message)
{
return new HttpErrorException(500, message);
}
// etc
}
throw HttpErrorException.BadRequest("You made a bad request!");
I'm using Compact Framework 3.5 / VS2008. I'm getting really odd behavior with TypeLoadException. The following code throws this error. The reason is a problem with the database connection. However for some unknown reason this inner exception is lost and is not contained in the TypeLoadException.
try
{
settingsFromDb = SettingsFromDbManager.Instance;
}
catch (Exception ex)
{
throw ex; // BREAKPOINT HERE
}
If we look at the SettingsFromDbManager class below it can be seen that it is a simple singleton class. The database error is occurring in the Load() method. I haven't included this code in the sample. If I put a breakpoint at the position indicated in the sample below I can see a database error. Unfortunately if I put a breakpoint in the position indicated in the code above then all I get is the TypeLoadException with no inner exception. There is nothing to indicate that a database problem occurred. This is bad :( Does anyone know why this strange behavior could be happening??
Cheers
Mark
public sealed class SettingsFromDbManager
{
static readonly SettingsFromDbManager _instance = new SettingsFromDbManager();
SettingsFromDbManager()
{
try
{
Load();
}
catch (Exception ex)
{
throw ex; // BREAKPOINT HERE
}
}
public static SettingsFromDbManager Instance
{
get
{
return _instance;
}
}
.... more code ...
}
** Update **
Thanks very much for all the great suggestions and help!
Pierre I used the test class you so kindly wrote. Here's the code I called it with. It must be a quirk of the Compact Framework I guess because when I examined the exception it was TypeLoadException with no inner exception :(
try
{
Fail.Test();
}
catch (Exception ex)
{
var x = ex.ToString(); // BREAKPOINT HERE
}
I think VinayC is probably correct about the reason. This is all a bit beyond my knowledge. Not sure what to do now. I don't want to give up my Singleton classes - they are useful. I'm using the "fourth version" Singleton pattern from http://csharpindepth.com/Articles/General/Singleton.aspx. I haven't used them before but seemed like a good idea to share the same instance of some utility classes around the application rather than creating and disposing them numerous times. Performance is a big issue with the Compact Framework.
* Update *
WOO HOO! All I had to do was change the Singleton class as follows. It instantiates the class in the property getter. Now my exceptions bubble to the surface as expected :)
public sealed class SettingsFromDbManager
{
static SettingsFromDbManager _instance = null;
SettingsFromDbManager()
{
try
{
Load();
}
catch (Exception ex)
{
throw new Exception("Error loading settings", ex);
}
}
public static SettingsFromDbManager Instance
{
get
{
if (_instance == null)
_instance = new SettingsFromDbManager();
return _instance;
}
}
.... more code ...
}
From what I know, static constructors may run on a different thread (or more specifically on different call chain) - its a guarantee from runtime that they will be invoked before type is accessed. Exception in the static constructor will mark type as not usable for the app domain. When type is accessed, you will get an TypeInitializationException (as per documentation) but exception occurred within type constructor will not come as inner exception because its not on same call chain - for that matter static constructor might had been executed quite before. Only puzzle out here is TypeLoadException instead of TypeIntializationException as Hans has pointed out.
Edit: Here's the article that explains lazy/eager semantics of type initializers. Your code can be eager implementation (i.e. static constructor may get invoked even before first access to type field)
There is no good reason why the exception raised in the static constructor would not show up in your original call location. However, I don't understand why you do not get the System.TypeInitializationException instead, which should be the exception thrown in case your static constructor fails.
Here is a piece of sample code which throws System.TypeInitializationException with an inner exception set to the "failed" exception:
class Fail
{
static Fail()
{
}
Fail()
{
throw new System.Exception ("failed");
}
static readonly Fail instance = new Fail ();
public static void Test()
{
}
}
I would investigate further to understand why you are getting a TypeLoadException instead, which should occur when an assembly cannot be properly loaded or initialized (TypeLoadException Class in MSDN).
I currently have this class that another programmer in my team coded:
public static class SoapExecuter
{
private static readonly ILog logger;
public static Exception ExecuterException { get; private set; }
public static bool IsSoapException
{
get
{
if (ExecuterException == null)
return false;
return ExecuterException.GetType() == typeof(SoapException);
}
}
public static bool Execute(Action action)
{
ExecuterException = null;
bool passed = false;
try
{
action();
passed = true;
}
catch (SoapException se)
{
ExecuterException = se;
logger.log(se);
}
catch (Exception ex)
{
ExecuterException = ex;
logger.log(ex);
}
return passed;
}
}
This is not very idiomatic and I would like to change it to something that happens within the try...catch clause.
Is there a way to not violate DRY and still stay within the idioms the language offers?
Of course I can inherit from the SoapException and log it but I'll have to catch a SoapException and create a new exception object that wraps it and then throw it only to be silenced one level above.
Any idea guys?
Sounds like what you really want is not to handle that exception inside Execute at all. The responsibility for handling the exception seems to lie with the code that calls Execute.
Of course you can still catch it, store it in ExecuterException, log it, and then rethrow it using throw; — but the purpose of ExecuterException eludes me. It seems that you only need it for IsSoapException, which in turn is much better written as ExecuterException is SoapException anyway, which even takes care of nullness and subclasses.
I don’t think anyone can be of any further help than this without seeing the code that uses the code you posted. If that code queries ExecuterException only immediately after calling Execute, then you can (and should) probably just change it to a try/catch in that code. If it actually queries ExecuterException elsewhere, then you could consider having that code store the reference instead, but either way, it would mean that the code is pretty entangled spaghetti code and probably requires a major rewrite anyway.
(By the way, just to nitpick, the first of the two catch clauses in your code is completely redundant. If you remove it you get exactly the same behaviour — unless logger.log has a special overload for SoapException, but then you should probably restructure that too.)
I've created class that takes Exception type in constructor
private readonly Exception _exception;
public StringToObject(Exception exception)
{
_exception = exception;
}
i wanted to throw exception
throw new _exception("");
but i got error:
'._exception' is a 'field' but is used like a 'type'
is any possible ways to throw it?
This is not a good practice at all. Doing so will cause you to lose your stack trace related information. Please consider reading this section of Eric Lippert's blog:
Too Much Reuse
When you write
throw new Exception();
you instantiate this new exception. But then, since your private member _exception is already instantiated, you don't need to re-instantiate it, that is instantiating an instance, which doesn't make sense. Instead, use the following:
throw _exception;
This will do it.
To rethrow an existing exception like that use
throw _exception;
However, that will modify the call stack in the exception instance, so you will lose the original source of the exception. If you want to avoid that, you can throw a new exception with the instance as an inner exception.
I'm actually very confused about why you want to do this? Are you trying to create a custom exception to provide more information? If so, then you want to use this pattern.
First define a custom exception class that derives from Exception:
public class MyCustomException : Exception // Or you could derive from ApplicationException
{
public MyCustomException(string msg, Exception innerException)
: base(msg, innerException)
{
}
}
You could also define additional parameters in your custom exception constructor to contain even more information if you wish. Then, in your application code...
public void SomeMethod()
{
try
{
// Some code that might throw an exception
}
catch (Exception ex)
{
throw new MyCustomException("Additional error information", ex);
}
}
You'll want to be sure to keep track of the inner exception, because that will have the most useful call stack information about what caused the exception in the first place.
throw _exception;
This example should work. I´ve included all the classes involved in the example.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
public class MyException : Exception
{
public MyException(string message) : base(message)
{}
//...
}
public class MyClass
{
private Exception exception;
public MyClass(Exception e)
{
this.exception = e;
}
public void ThrowMyException()
{
throw exception;
}
}
class Program
{
static void Main(string[] args)
{
MyException myExceptionInstance = new MyException("A custom message");
MyClass myClassInstance = new MyClass(myExceptionInstance);
myClassInstance.ThrowMyException();
}
}
}
I suspect that what you're really looking for is to throw a new exception of your suggested type, in which case passing in a "Type" parameter (or even using a generic) would be the way forward.
However, I can't imagine a situation where this is a sensible design choice, so I'd have to urge you to reconsider (and perhaps post more of your requirements so that someone can suggest a better alternative!).