CODEWITHSUNDEEP
c#vb.nettry-catchcompiler-warnings
Jens
Jens

Reputation: 6375

Avoiding debugger warning in IsNothing() statement

I am using Visual Studio 2012 and have the following code block. The code checks the file type of a specific file (that's why there are return True/False in it). If it encounters an error it also returns false. The warnings I get are that I use the fs/br variables before they are initialized, which is true. That's why I have the IsNothing statements, but I get the warning IN the IsNothing statements and I have no idea how to avoid that because I don't want to put the fs = New FileStream(fn, FileMode.Open) and br = ... statements outside the Try/Catch block.

The code itself works so the warning is not really a problem, but it still bothers me to have them. Does anyone see a solution how this block can be changed to offer the same safety without warnings?

Both VB.NET or C# answers are welcome.

            Dim fs As FileStream
            Dim br As BinaryReader
            Try
                fs = New FileStream(fn, FileMode.Open) 'Open the file
                br = New BinaryReader(fs) 'Initilize the reader
                'File reading code omitted here
                br.Close() 'Close the reader and underlying stream
            Catch
                If Not IsNothing(fs) Then fs.Close() 'Warning here
                If Not IsNothing(br) Then br.Close() 'and here
                Return False
            End Try

Upvotes: 1

Views: 153

Answers (2)

Matt Wilko
Matt Wilko

Reputation: 27322

You can re-write this without having to use a nested Using block -you can do it all in one line - I don't believe you can do this in C#:

    Try
        Using fs As New FileStream(fn, FileMode.Open), br As New BinaryReader(fs)
            Try

            Catch ex As Exception
                'an exception here indicates an issue reading the file
            End Try
        End Using
    Catch ex As Exception
        'an exception here indicates an issue opening the filestream or reader
    End Try

The using block ensures that the objects are disposed of without the need to explicitly call .Dispose it also calls .Close so you don't even need that line

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1499860

That's why I have the IsNothing statements

That suggests you expect the values to be IsNothing before they're given a specific value. In C#, this wouldn't just be a warning - it would be an error.

I have two suggestions:

  • If you really want to follow this pattern, just set the values to Nothing to start with:

    Dim fs As FileStream = Nothing
Dim br As BinaryReader = Nothing
  • If at all possible, reorganize your code so you can just use Using statements instead, which will close the streams at the end of the block either way. We can't tell enough about the rest of the code to help you do that at the moment though.

Upvotes: 2

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