SynchronizationContext.Post to UI Method

Question

I\'m working with web services so its necessary for me to extend session length/reconnect and get large datasets back etc. Sometimes this can be lengthy so I wanted it in a

Answer 1

Typically you are creating instances of your types (e.g. ViewModels) on the UI thread, so you can just save the SynchronizationContext or the TaskScheduler (preferable IMHO) to a private field and then compare it when needed...

private readonly SynchronizationContext _syncContext = SynchronizationContext.Current;
private readonly TaskScheduler _scheduler = TaskScheduler.Current;

void OnSomeEvent(object sender, EventArgs e)
{
    if (_syncContext != SynchronizationContext.Current)
    {
        // Use Send if you need to get something done as soon as possible.
        // We'll be polite by using Post to wait our turn in the queue.
        _syncContext.Post(o => DoSomething(), null);
        return;
    }
    // Call directly if we are already on the UI thread
    DoSomething();
}

void OnSomeOtherEvent(object sender, MyEventArgs e)
{
    var arg1 = e.Arg1; // "Hello "
    var arg2 = e.Arg2; // {"World", "!"};

    // Process args in the background, and then show the result to the user...
    // NOTE: We don't even need to check the context because we are passing
    // the appropriate scheduler to the continuation that shows a MessageBox.

    Task<string>.Factory.StartNew(() => ReturnSomething(arg1, arg2))
        .ContinueWith(t => MessageBox.Show(t.Result), _scheduler);
}

void DoSomething() { MessageBox.Show("Hello World!"); }

string ReturnSomething(string s, IEnumerable<string> list)
{
    return s + list.Aggregate((c, n) => c + n);
}

Answer 2

You need a delegate of type SendOrPostCallback. Which is pretty awkward, it only takes a single argument of type object. You definitely ought to look at the Task<> class available in .NET 4 to make this easier. Or use a lambda, like this:

        string conn_name = "foo";
        uiContext.Post(new SendOrPostCallback((o) => {
            updateConnStatus(conn_name, true);
        }), null);

The code between the { braces } executes on the UI thread.