Windows Phone ContactPicker won't await properly

Question

Although this has been posted before on StackOverflow but i think none of those reflect my issue and none of those solutions work for me either. So i'm developing a Windows Phone app and my workflow is a bit like this:

App starts
ContactPicker opens up
User selects one or multiple contacts
Based on how many contacts he selected, that many PivotItems are added into the Pivot.

My code is as follows:

    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        // TODO: Prepare page for display here.

        // TODO: If your application contains multiple pages, ensure that you are
        // handling the hardware Back button by registering for the
        // Windows.Phone.UI.Input.HardwareButtons.BackPressed event.
        // If you are using the NavigationHelper provided by some templates,
        // this event is handled for you.

        SelectContacts();
    }

    private async Task SelectContacts()
    {
        var picker = new ContactPicker();
        picker.DesiredFieldsWithContactFieldType.Add(ContactFieldType.PhoneNumber);

        ContactsList = (List<Contact>)await picker.PickContactsAsync();
        DisplayContacts();
    }

    private void DisplayContacts()
    {
        if (ContactsList != null)
        {
            foreach (var item in ContactsList)
            {
                PivotItem pivotItem = new PivotItem();
                pivotItem.Header = item.FirstName.ToString();

                ContentRoot.Items.Add(pivotItem);
            }
        }
    }

According to me, in SelectContacts() method, the app should wait at the await call and once it gets back the list of contacts, than it should execute the DisplayContacts() method but its not working. I've tried multiple other variations of this code and they aren't working either.

@i3arnon it's not running in the correct order. Anything after await should be run once that line has completely executed but in my case it doesn't wait for the await line to completely execute. — Haseeb Ahmed, Feb 07 '15 at 08:40
What do you mean by "anything after the await". I assure you that `DisplayContacts` will only run after the awaited operation completed. Is there something else? — i3arnon, Feb 07 '15 at 08:43
@i3arnon that is the exact problem. DisplayContacts runs before the await is completed. I know it shouldn't do that but it is. — Haseeb Ahmed, Feb 08 '15 at 06:32
I find that hard to believe. What happens if you call PickContactAsync().Result does it act the same? — i3arnon, Feb 08 '15 at 06:40
Then `PickContactsAsync` has definitively completed. Why do you think it shouldn't? — i3arnon, Feb 09 '15 at 14:20
@i3arnon its not completed because i can see the contact picker on the screen and I've selected no contact. — Haseeb Ahmed, Feb 09 '15 at 15:22
maybe you found a bug in `PickContactsAsync` but there's no doubt await completed. What's stored in `ContactsList ` when it continues? — i3arnon, Feb 09 '15 at 15:35
@i3arnon It shouldn't be a bug. Works in a older app of mine. ContactsList is null when it continues. — Haseeb Ahmed, Feb 10 '15 at 13:25

score 1 · Answer 1 · answered Feb 07 '15 at 05:02

1

await the SelectContacts() method and add the DisplayContacts() method beneath it. Remove the DisplayContacts() method from SelectContacts()

await SelectContacts();
DisplayContacts();

answered Feb 07 '15 at 05:02

Tim Southard

604
4
16

Tried that as well. Doesn't work. I can still see the ContactPicker running on my emulator while DisplayContacts() doesn't wait for SelectContacts() and starts executing. – Haseeb Ahmed Feb 07 '15 at 05:06
Try not casting the await as List. Instead, do something like 'var contacts = await picker.getContactsAsync(); if (contacts != null) ContactsList = (List)contacts;' – Tim Southard Feb 07 '15 at 05:15

score 0 · Accepted Answer · answered Feb 11 '15 at 17:04

I don't know the complete reason why but i figured it out that since i was making the PickContactsAsync() call in the OnNavigatedTo() event, that is why it wasn't working as expected. Once i moved the PickContactsAsync() call into the PageLoaded() event handler, it started working as usual.

Windows Phone ContactPicker won't await properly

2 Answers2