Why exception is raised and correcting it

Question

1.67/5 (3 votes)

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.NET4.5

VS2015

I have an xml File named as History.xml and also corresponding History.vb which contains only two properties namely TItleName and FileName.
The Obj returned is correct. But Community 2015 while debugging, when executing the line following Try immediately proceeds to Throw with an exception in output as follows:
Exception thrown: 'System.IO.FileNotFoundException' in mscorlib.dll

The obj returned contains all objects that are found in history.xml file.

The following code in full is used for deserializing history.xml file.

VB

Public Shared Function InitializeCollectionSource(Of T)(path As String) As ObservableCollection(Of T)
        Dim obj As ObservableCollection(Of T) = New ObservableCollection(Of T)
        If Not File.Exists(path) Then Return obj
        Using reader = New FileStream(path, FileMode.Open)
            Dim serializer = New XmlSerializer(obj.GetType)
            Try
                obj = CType(serializer.Deserialize(reader), ObservableCollection(Of T))
            Catch ex As Exception
                Throw
            Finally
                serializer = Nothing
            End Try
        End Using

        Return obj
    End Function

The following is my questions:
1. Please inform me as to Why exception is thrown.
2. Also please suggest as to What is to be done to correct it.
Thanks.

After Comment:
With due respect, gentlemen, the class that is deserialized has parameterless constructor. Also, tostring, GetHashCode and Equals are implemented. I have stated already, that the initialization works well, ie. object deserialized is complete. Please review your comments.

Posted 27-Oct-15 1:19am

Sesharaman

Updated 27-Oct-15 17:43pm

v3

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Comments

Richard MacCutchan 27-Oct-15 9:43am

When you catach an exception you should display the details, so you can find out what is wrong with your code.

bojammis 27-Oct-15 11:52am

I agree with Richard, you need to review the exception message. Some common areas to consider: XML can serialize an object if the object has a parameter-less constructor(this gets me every time). Also properties of other object must have parameter-less constructors. The exception message will indicate what property failed to initialize if this is the case.

Sergey Alexandrovich Kryukov 28-Oct-15 2:13am

"Catch ex As Exception
Throw"
is totally pointless, misuse of exceptions. Another misuse is local exception handling. It would be justified if "finally" was needed, but assignment of the reader to null is another, third misuse.

—SA

Philippe Mori 30-Oct-15 9:51am

What is the missing file as indicated in the exception message. This is the most important information but yet it is not provided.

In fact, if the filename contains XmlSerializers in it name then it is a completly different issue than if the file name is the same as path.

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Philippe Mori · Accepted Answer · 2015-10-30T02:20:00

Assuming that the problem is with serialization assemblies as otherwise it should be trivial to know why it fails....

If we tell the debugger to stop on all exception, it will stop even if an exception in handled by the framework...

A Google search of XML serialization FileNotFoundException would give a lot of links.

https://www.google.ca/?client=safari&channel=ipad_bm#channel=ipad_bm&q=xml+serialization+filenotfoundexception[^]

First two results:

http://stackoverflow.com/questions/8764742/filenotfoundexception-when-deserializing-xml[^]
http://stackoverflow.com/questions/1127431/xmlserializer-giving-filenotfoundexception-at-constructor[^]

Thus this "problem" is well known so better to use Google that to ask same kind of question yet another time...

If you otherwise don't care for FileNotFoundException, then you can uncheck that specific option in you exception settings.

It would be nice if there would be a way to disable those exceptions in specific cases but it is either on or off switch...

NullReferenceException and TimeoutException are other exceptions that you would generally want to stop on them but not always.

Resources in ASP.NET is another case where you sometime have to handle exceptions if you want to find strings in multiple locations in a defined order as there a no function to test if a specific resource exists (well there might be some way to do it but not as easy as as TrySomething function...)

Other links will probably tell how to fix that but I never tried it. I simply ignore that in my own application as the application works as expected anyway.