Identifying Exception Type in a handler Catch Block

Question

I have created custom exception class  public class Web2PDFException   Exception       public Web2PDFException string message  Exception innerException            base message  innerException              In my application how can I find out if it is my custom exception or not    try            catch  Exception err      Find exception type here

User · Answer

Alternatively   var exception   err as Web2PDFException    if   excecption    null            Web2PDFException wex   exception

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When dealing with situations where I don t exactly know what type of exception might come out of a method  a little  trick  I like to do is to recover the Exception s class name and add it to the error log so there is more information   try       lt code gt     catch   Exception caughtEx        throw new Exception  Unknown Exception Thrown                               n  Type         caughtEx GetType   Name                            n  Message      caughtEx Message       I do vouch for always handling Exceptions types individually  but the extra bit of info can be helpful  specially when dealing with code from people who love to capture catch-all generic types

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Alternative Solution    Instead halting a debug session to add some throw-away statements to then recompile and restart  why not just use the debugger to answer that question immediately when a breakpoint is hit   That can be done by opening up the Immediate Window of the debugger and typing a GetType off of the exception and hitting Enter  The immediate window also allows one to interrogate variables as needed   See VS Docs  Immediate Window     For example I needed to know what the exception was and just extracted the Name property of GetType as such without having to recompile

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You should always catch exceptions as concrete as possible  so you should use   try         code   catch  Web2PDFException ex          Handle the exception here     You chould of course use something like this if you insist   try     catch  Exception err        if  err is Web2PDFException                  Code

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you can add some extra information to your exception in your class and then when you catch the exception you can control your custom information to identify your exception  this Data  mykey    keyvalue     you can add any type of data if you want    and then you can get your value  string mystr    string  err Data  mykey      like that for more information  http   msdn microsoft com en-us library system exception data aspx

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try          Some code   catch  Web2PDFException ex           It s your special exception   catch  Exception ex           Any other exception here

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UPDATED  assuming C  6  the chances are that your case can be expressed as an exception filter  This is the ideal approach from a performance perspective assuming your requirement can be expressed in terms of it  e g    try     catch   Web2PDFException ex   when   ex Code    52           Assuming C   lt  6  the most efficient is to catch a specific Exception type and do handling based on that  Any catch-all handling can be done separately  try     catch   Web2PDFException ex         or  try     catch   Web2PDFException ex       catch   Exception ex         or  if you need to write a general handler - which is generally a bad idea  but if you re sure it s best for you  you re sure     if  err is Web2PDFException          or  in certain cases if you need to do some more complex type hierarchy stuff that cant be expressed with is    if  err GetType   IsAssignableFrom typeof Web2PDFException            or switch to VB NET or F  and use is or Type IsAssignableFrom in Exception Filters

User · Answer

try     catch  Exception err        if  err is Web2PDFException          DoWhatever        but there is probably a better way of doing whatever it is you want

[c#] Identifying Exception Type in a handler Catch Block

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