Question

What is happening when I close a form, which was opened using Show(), by using Dispose() instead of Close()? Can someone tell me in detail, what happening in the Dispose() method?

Answer 1

The basic difference between Close() and Dispose() is, when a Close() method is called, any managed resource can be temporarily closed and can be opened once again. It means that, with the same object the resource can be reopened or used. Where as Dispose() method permanently removes any resource ((un)managed) from memory for cleanup and the resource no longer exists for any further processing.

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Or just a general statement. With the connection object calling Close() will release the connection back into the pool. Calling Dispose() will call Close() and then set the connection string to null.

Some objects such as a Stream implement IDisposable but the Dispose method is only available if you cast the object to an IDisposable first. It does expose a Close() method though.

I would always argue that you should call Dispose() on any object that implements IDisposable when you are through with the object. Even if it does nothing. The jit compiler will optimize it out of the final code anyway. If the object contains a Close() but no Dispose() then call Close().

You can also use the using statement on IDispoable objects

using(SqlConnection con = new SqlConnection())
{
    //code...
}

This will call Dispose() on the SqlConnection when the block is exited.