Question

I used to dispose elements of type :

SqlConnection
SqlDataAdapter
DataSet etc.

But i am not sure whether it is needed to dispose for objects of type:

    string[] str = ;
    ArrayList etc.

Object of some class

If it is needed..Please tell me if it is ok just to dispose it this way

If(str != null)
{
  str = null;
}

Please suggest me if any better way is there to address this.

Answer 1

No, only objects implementing the IDisposable interface need to be deterministacally disposed of. Ideally you should wrap them in using statement and not call the .Dispose method manually:

using (var conn = new SqlConnection(ConnectionString))
using (var cmd = conn.CreateCommand())
{
    conn.Open();
    cmd.CommandText = "SELECT foo FROM bar";
    using (var reader = cmd.ExecuteCommand())
    {
        while (reader.Read())
        {
            // TODO: consume your resultset
        }
    }
}

or streams:

using (var stream = new MemoryStream())
{
    ...
}

or files:

using (var file = File.OpenRead())
{
    ...
}

or readers:

using (var reader = XmlReader.Create("foo.xml"))
{
    ...
}

The IDisposable pattern is used in .NET when an object is holding references to unmanaged objects that need to be disposed and the CLRT cannot track and dispose those unmanaged resources automatically. In this case it is up to the developer to dispose them deterministically as soon as he has finished using them (by wrapping them in using statements as shown previously). For all other objects that do not implement the IDisposable interface you should leave the memory menagement to the CLR and the Grbage Collector which will track them and automatically release the memory they are holding when no more references are pointing to them. You, as a developer should not worry about it.

So here’s the rule of thumb:

When you instantiate some variable, if this variable implements IDisposable then wrap it in a using statement, if not, then leave it to the Garbage Collector.