WPF code analyze : CA2202 Do not dispose objects multiple timesObject

Question

in my WPF application code i got the following Warnings:

CA2202 Do not dispose objects multiple times Object 'fs' can be disposed more than once in method 'MainWindow.TestResults_Click(object, RoutedEventArgs)'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object. : Lines: 429 yesMonitor MainWindow.xaml.cs 429

for code:

FileStream fs = new FileStream(System.AppDomain.CurrentDomain.BaseDirectory + "TestResult.htm", FileMode.Create);
using (fs)
{
    using (StreamWriter w = new StreamWriter(fs, Encoding.UTF8))
    {
        w.WriteLine(GetTestResultsHtml());
    }
}

what should be the reason for these warning?

Answer 1

Nested using statements can cause violations of the CA2202 warning. If the IDisposable resource of the nested inner using statement contains the resource of the outer using statement, the Dispose method of the nested resource releases the contained resource. When this situation occurs, the Dispose method of the outer using statement attempts to dispose its resource for a second time. In the following example, a Stream object that is created in an outer using statement is released at the end of the inner using statement in the Dispose method of the StreamWriter object that contains the stream object. At the end of the outer using statement, the stream object is released a second time. The second release is a violation of CA2202.

using (Stream stream = new FileStream("file.txt", FileMode.OpenOrCreate))
{
    using (StreamWriter writer = new StreamWriter(stream))
    {
        // Use the writer object...
    }
}

To resolve this issue, use a try/finally block instead of the outer using statement. In the finally block, make sure that the stream resource is not null.

Stream stream = null;
try
{
    stream = new FileStream("file.txt", FileMode.OpenOrCreate);
    using (StreamWriter writer = new StreamWriter(stream))
    {
        stream = null;
        // Use the writer object...
    }
}
finally
{
    if(stream != null)
        stream.Dispose();
}

Answer 2

Personally in this case I would use:

public StreamWriter(
    string path,
    bool append
)

Initializes a new instance of the StreamWriter class for the specified file by using the default encoding and buffer size. If the file exists, it can be either overwritten or appended to. If the file does not exist, this constructor creates a new file.

But there is NO good solution, see CA2202, how to solve this case