Code analysis warns about a potential of disposing of an object twice

Question

Just ran a code analysis on one of the applications I inherited, and it raised warnings about code similar to the following:

using (StreamWriter tw = File.AppendText("Log.txt"))
{
    try
    {
        tw.WriteLine(DateTime.Now.ToString("------------------------");
        tw.WriteLine(data);
    }
    catch(Exception ex)
    {
        Console.WriteLine(String.Format(CultureInfo.InvariantCulture, "Error writing to the log file: {0}", ex.Message));
    }
    finally
    {
        tw.Close();
    }
}

If I comment out the finally block, the warning is not raised. I was under impression that closing a stream writer only closed the underlying file, but did not actually dispose of the writer object. Is code analysis broken, or am I misunderstanding how stream writer should be used?

Here's another example where code analysis complains about possible disposing of both writer and the underlying stream twice:

using (TextReader tr = new StreamReader(File.OpenRead(filename)))
{
    while (tr.ReadLine() != null)
    {
        counter++;
    }

    tr.Close();
}

It complains about both tr and File.OpenRead(filename)

Answer 1

Close just calls Dispose on the object, so yes, you're disposing of the object twice. (Not that disposing of an object twice is problematic, just redundant.)