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Question

I have made a method that lists all of the ftp folders in a path.
My problem is that I need to return this as an array.
But it is a background worker, and I can only return it to the "RunWorkerCompleted",
with e.Result.
1) How can I pass a parameter to the method?(of the background-worker)
2) How can I return the array of folders to a normal method?
Like so:

private void btnOpen_Click_1(object sender, EventArgs e)
        {
           string[]/List... a=  getDirectories(**path**)?
        }

Answer 1

You can have a List as a member of the form itself, and have the worker add into that as it does it's work (since the worker code will belong to the form, the member will be in scope).

Therefore if you want the worker to add its items into a specific instance of a list; just set that into the member first before triggering the worker.

However you must be careful with this approach not to access that list whilst the worker is running; as it's not thread safe. In .Net 4 you could use the ConcurrentBag - which is thread-safe.

If you don't want to do that, then the Result member of the event arguments passed in the RunWorkerCompleted event is, as you say, used to communicate results - and that is where you would return your list. You can also use the ProgressChanged event ( on MSDN ) to stream back individual snapshot of results as well.

I don't think this is unreasonable: async operations are a fundamentally different paradigm to synchronous calls, you simply can't use the same call-and-return semantics.

Answer 2

You can pass your arguments as they are objects. BackgroundWorker takes a parameter of object . A variable of object can carry anything: array, references and variables.

Example:

object[] args = new object[] { fileName, ....... };
this.backgroundWorker1.RunWorkerAsync(args);

in the method:

void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            object o = e.Argument;
            object[] args = (object[])o;
            string fileName = (string)args[0];
            ....
            object[] result = ....
            e.Result = result;
        }

When the work has completed:

void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {

            object o = e.Result;
            object[] result = (object[])o;
            ...
        }