If I return a value inside a using block in a method, does the using dispose of the object before the return?

问题

I'm going through some old C#.NET code in an ASP.NET application making sure that all SqlConnections are wrapped in using blocks.

I know that using is the same as try / finally where it disposes of the object in the finally no matter what happens in the try. If I have a method that returns a value inside the using, even though execution leaves the method when it returns, does it still call .Dispose() on my object before/during/after it's returning?

public static SqlCommand getSqlCommand(string strSql, string strConnect){
    using (SqlConnection con = new SqlConnection(strConnect))
    {
        con.Open();
        SqlCommand cmd = GetSqlCommand();
        cmd.Connection = con;
        cmd.CommandText = strSql;
        return cmd;
    }
}

Update: The accepted answer is the one I think best answers my question but note that this answer caught the stupidity of this code, that I'm returning a command that uses a disposed connection! :P

回答1:

Yes it will still call dispose.

Run this very simple console application top verify:

   class Program
    {
        static void Main(string[] args)
        {
            TestMethod();
            Console.ReadLine();
        }

        static string TestMethod()
        {
            using (new Me())
            {
                return "Yes";
            }
        }
    }

    class Me : IDisposable
    {
        #region IDisposable Members

        public void Dispose()
        {
            Console.WriteLine("Disposed");
        }

        #endregion
    }

回答2:

Yes. It will dispose of your object. This will actually cause a problem in your code, since the SqlCommand being returned is dependent on the SqlConnection, which will be Disposed of prior to the control flow returning to your caller.

You can, however, use delegates to work around this. A good pattern to handle this is to rewrite your method like so:

public static SqlCommand ProcessSqlCommand(string strSql, string strConnect, Action<SqlCommand> processingMethod)
{ 
    using (SqlConnection con = new SqlConnection(strConnect)) 
    { 
        con.Open(); 
        SqlCommand cmd = GetSqlCommand(); 
        cmd.Connection = con; 
        cmd.CommandText = strSql; 
        processingMethod(cmd); 
    } 
}

You can then call this like:

ProcessSqlCommand(sqlStr, connectStr, (cmd) =>
    {
        // Process the cmd results here...
    });

来源：https://stackoverflow.com/questions/2313196/if-i-return-a-value-inside-a-using-block-in-a-method-does-the-using-dispose-of

标签

.net

idisposable