Silverlight, dealing with Async calls

Question

I have some code as below:

        foreach (var position in mAllPositions)
        {
                 DoAsyncCall(position);
        }
//I want to execute code here after each Async call has finished

So how can I do the above?
I could do something like:

        while (count < mAllPositions.Count)
        { 
            //Run my code here
        }

and increment count after each Async call is made ... but this doesn't seem like a good way of doing it

Any advice? Is there some design pattern for the above problem as i'm sure it's a common scenario?

Answer 1

Given that you're using Silverlight, and you don't have access to Semaphores, you might be looking for something like this (written in notepad, so no promises as to perfect syntax):

int completedCallCount = 0;
int targetCount = mAllPositions.Count;

using (ManualResetEvent manualResetEvent = new ManualResetEvent(false))
{
    proxy.DoAsyncCallCompleted += (s, e) =>
    {
        if (Interlocked.Increment(ref completedCallCount) == targetCount)
        {
            manualResetEvent.Set();
        }
    };

    foreach (var position in mAllPositions)
    {
        proxy.DoAsyncCall(position);
    }

    // This will wait until all the events have completed.
    manualResetEvent.WaitOne();
}

However, one of the benefits of Silverlight forcing you to asynchronously load data is that you have to work hard to lock the UI up when making a service calls, which is exactly what you're going to do with code like this, unless you have it running on a background thread, which I strongly recommend you do. You can always display a "please wait" message until the background process completes.