How to wait until await / async methods finish

Question

I have the following Async method:

private async void ProcessSearch()
{
    // get catalogs on first search
    if (_invoiceTypes == null && _invoice         


        

Answer 1

Minor changes to what you've got there will do what you want. You can start new tasks and then do other stuff and then await just before you go on. As @Noseratio has helpfully pointed out, this snippet below isn't production-ready because I'm not checking for error conditions (like null references, etc). The point is that you can succinctly and elegantly do these things in parallel without having to resort to using very much of the Tasks API. One adjustment I made worth pointing out is that you want to move the calls to Dispose into the continuation (i.e., after all your awaits) because if you try to Dispose right after calling the *Async methods you stand a good chance of killing off your WCF clients halfway through getting a response and the awaits will probably wind up throwing exceptions (which I'm not catching).

private async void ProcessSearchAsync()
{

    Data.ConfigurationWCF confWcf = new Data.ConfigurationWCF();
    Task</*typeof _invoiceTypes*/> t1;
    Task</*typeof _invoiceAccounts*/> t2;

    // get catalogs on first search
    if (_invoiceTypes == null && _invoiceAccounts == null)
    {
        t1 = confWcf.GetInvoiceTypesAsync(MainForm.State.Entity);
        t2 = confWcf.GetInvoiceAccountsAsync(MainForm.State.Entity);
    }

    DataSeekWCF seekWcf = new DataSeekWCF();
    Task</*typeof _ds*/> t3 = seekWcf.SearchInvoiceAdminAsync(new Guid(cboEmployer.Value.ToString()), new Guid(cboGroup.Value.ToString()), txtSearchInvoiceNumber.Text, chkSearchLike.Checked, txtSearchFolio.Text, Convert.ToInt32(txtYear.Value));

    _invoiceTypes = await t1;
    _invoiceAccounts = await t2;
    _ds = await t3;

    if (_ds != null)
    {
        SetupInvoiceGrid();
    }

    confWcf.Dispose();
    seekWcf.Dispose();
}

Answer 2

I answered the original(?) question on how to handle the finish of ProcessSearchAsync itself here.

To run tasks in parallel (as asked in the comments), here's your code modified, it gets a little complicated because of invoiceTypes == null and _invoiceAccounts == null checks. Note the way the checks are implemented below slightly changes the logic (previously it did WCF calls only if both _invoiceTypes and _invoiceAccounts were null - what if only one of them is null?):

private async Task ProcessSearchAsync()
{

    Data.ConfigurationWCF confWcf = new Data.ConfigurationWCF();
    Task</*typeof _invoiceTypes*/> t1;
    Task</*typeof _invoiceAccounts*/> t2;

    if (_invoiceTypes == null)
        t1 = confWcf.GetInvoiceTypesAsync(MainForm.State.Entity);
    else
    {
        var tsc1 = new TaskCompletionSource</*typeof _invoiceTypes*/>();
        t1 = tsc1.Task;
        tsc1.SetResult(_invoiceTypes);
    }

    if ( _invoiceAccounts == null )
        t2 = confWcf.GetInvoiceAccountsAsync(MainForm.State.Entity);
    else
    {
        var tsc2 = new TaskCompletionSource</*typeof _invoiceAccounts*/>();
        t2 = tsc2.Task;
        tsc2.SetResult(_invoiceAccounts);
    }


    DataSeekWCF seekWcf = new DataSeekWCF();
    Task</*typeof _ds*/> t3 = seekWcf.SearchInvoiceAdminAsync(new Guid(cboEmployer.Value.ToString()), new Guid(cboGroup.Value.ToString()), txtSearchInvoiceNumber.Text, chkSearchLike.Checked, txtSearchFolio.Text, Convert.ToInt32(txtYear.Value));

    await Task.WhenAll(new Task[] {t1, t2, t3});
    _invoiceTypes = t1.Result;
    _invoiceAccounts = t2.Result;
    ds = t3.Result;

    if (_ds != null)
    {
        SetupInvoiceGrid();
    }

    confWcf.Dispose();
    seekWcf.Dispose();
}