访问委托中的修改后的闭包

Question

I'm working with TaskCompletionSource. I register event on object, but when I try to unregister in my event method, resharper underlines it with note: Access to modified closure.

here is my code

var taskCompletionSource = new TaskCompletionSource<bool>();
OnConnectionStateChangedInd handlerConnectionStateChangedInd = null;
OnBootCompletedCnfCallback handlerBootCompletedCnfCallback = null;

handlerConnectionStateChangedInd = (id, method, addr, port, nick) =>
{
    _corePttObject.onConnectionStateChangedInd -= handlerConnectionStateChangedInd;
    _connectionState = id;

    taskCompletionSource.SetResult(true);
};
_corePttObject.onConnectionStateChangedInd += handlerConnectionStateChangedInd;

This line is underlined:

_corePttObject.onConnectionStateChangedInd -= handlerConnectionStateChangedInd;

Here is my complete definition of method:

public Task<LoginResult> LoginAsync(string address)
    {
        var taskCompletionSource = new TaskCompletionSource<LoginResult>();
        OnUserAcceptCertWithNamePasswInd handlerAcceptCertWithNamePasswInd = null;
        OnAppExLoginProtocolServiceCnf handlerAppExLoginProtocolServiceCnf = null;
        handlerAcceptCertWithNamePasswInd = (cert, caCert, rootCert, hash, pos, data) =>
        {
            var loginCompletedArgs = new LoginResult
            {
                SvrCertificate = ParseCertificate(cert),
                CaCertificate = ParseCertificate(caCert),
                RootCertificate = ParseCertificate(rootCert),
                CertificateHash = hash,
                GridPosition = pos,
                GridData = data
            };
            _corePttObject.onUserAcceptCertWithNamePasswInd -= handlerAcceptCertWithNamePasswInd;
            taskCompletionSource.SetResult(loginCompletedArgs);
        };

        handlerAppExLoginProtocolServiceCnf = (nick, result, cause, link) =>
        {
            _corePttObject.onAppExLoginProtocolServiceCnf -= handlerAppExLoginProtocolServiceCnf;
        };

        _corePttObject.onAppExLoginProtocolServiceCnf += handlerAppExLoginProtocolServiceCnf;
        _corePttObject.onUserAcceptCertWithNamePasswInd += handlerAcceptCertWithNamePasswInd;
        //TODO: read id.
        _corePttObject.Login(address, true, "ID");

        return taskCompletionSource.Task;
    }

Answer 1

If you click click on the lightbulb suggestion, there will be an option "Why is ReSharper suggesting this". If you click on it, it will take you to this useful explanation .

I'd need more context to tell if this potential trap can actually hurt you in your particular case.

You can also check out this answer here .

Answer 2

The reason for this warning is: for handlerConnectionStateChangedInd you declare an anonymous method that - when eventually executed - will access/change _corePttObject.onConnectionStateChangedInd .

Then, after this declaration, you change _corePttObject.onConnectionStateChangedInd already in this line:

_corePttObject.onConnectionStateChangedInd += handlerConnectionStateChangedInd;

So ReSharper is warning you that the value _corePttObject.onConnectionStateChangedInd is different between the time you declare handlerConnectionStateChangedInd and the time it is executed.