CA2202, how to solve this case

.net, c#, code-analysis, fxcop

Solution

This compiles without warning:

    public static byte[] Encrypt(string data, byte[] key, byte[] iv)
    {
        MemoryStream memoryStream = null;
        DESCryptoServiceProvider cryptograph = null;
        CryptoStream cryptoStream = null;
        StreamWriter streamWriter = null;
        try
        {
            memoryStream = new MemoryStream();
            cryptograph = new DESCryptoServiceProvider();
            cryptoStream = new CryptoStream(memoryStream, cryptograph.CreateEncryptor(key, iv), CryptoStreamMode.Write);
            var result = memoryStream;              
            memoryStream = null;
            streamWriter = new StreamWriter(cryptoStream);
            cryptoStream = null;
            streamWriter.Write(data);
            return result.ToArray();
        }
        finally
        {
            if (memoryStream != null)
                memoryStream.Dispose();
            if (cryptograph != null)
                cryptograph.Dispose();
            if (cryptoStream != null)
                cryptoStream.Dispose();
            if (streamWriter != null)
                streamWriter.Dispose();
        }
    }

Edit in response to the comments: I just verified again that this code does not generate the warning, while the original one does. In the original code, `CryptoStream.Dispose()` and `MemoryStream().Dispose(`) are actually called twice (which may or may not be a problem).

The modified code works as follows: references are set to `null`, as soon as responsibilty for disposing is transferred to another object. E.g. `memoryStream` is set to `null` after the call to `CryptoStream` constructor succeeded. `cryptoStream` is set to `null`, after the call to `StreamWriter` constructor succeeded. If no exception occurs, `streamWriter` is disposed in the `finally` block and will in turn dispose `CryptoStream` and `MemoryStream`.

Problem

Can anybody tell me how to remove all CA2202 warnings from the following code? ``` public static byte[] Encrypt(string data, byte[] key, byte[] iv) { using(MemoryStream memoryStream = new MemoryStream()) { using (DESCryptoServiceProvider cryptograph = new DESCryptoServiceProvider()) { using (CryptoStream cryptoStream = new CryptoStream(memoryStream, cryptograph.CreateEncryptor(key, iv), CryptoStreamMode.Write)) { using(StreamWriter streamWriter = new StreamWriter(cryptoStream)) { streamWriter.Write(data); } } } return memoryStream.ToArray(); } } ``` Warning 7 CA2202 : Microsoft.Usage : Object 'cryptoStream' can be disposed more than once in method 'CryptoServices.Encrypt(string, byte[], byte[])'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 34 Warning 8 CA2202 : Microsoft.Usage : Object 'memoryStream' can be disposed more than once in method 'CryptoServices.Encrypt(string, byte[], byte[])'. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.: Lines: 34, 37 You need Visual Studio Code Analysis to see these warnings (these are not c# compiler warnings).

Original source