Question

I’ve got the following combobox defined:

<ComboBox x:Name="cmbCurrency" 
          ItemsSource="{Binding IsoCurrenciesList}"
          DisplayMemberPath="Description"
          SelectedValuePath="LocaleID"
          SelectedValue="{Binding CurrencyId, Mode=TwoWay">
</ComboBox>

Where IsoCurrenciesList is an IEnumerable<IsoCurrency> – the type being defined by us and declared in the view model as:

private IEnumerable<IsoCurrency> isoCurrenciesList;
public IEnumerable<IsoCurrency> IsoCurrenciesList
{
    get { return isoCurrenciesList; }
    set
    {
        isoCurrenciesList = value;
        RaisePropertyChangedEvent("IsoCurrenciesList");
    }
}

My unit test creates an instance of the view and view model and sets up some dummy currency data in a local list:

[TestInitialize]
public void TestInit()
{
    _target = new View();

    _viewModel = new ViewModel();

    var ukp = new IsoCurrency { Code = "GBP", Description = "Pound Sterling", LocaleID = 826 };
    var usd = new IsoCurrency { Code = "USD", Description = "US Dollar", LocaleID = 840 };
    var eur = new IsoCurrency { Code = "EUR", Description = "Euro", LocaleID = 978 };
    _currencies = new List<IsoCurrency> { ukp, usd, eur };

    GetUIElement<Grid>("LayoutRoot").DataContext = _viewModel;
}

private T GetUIElement<T>(string name) where T : UIElement
{
    return (T)_target.FindName(name);
}

Then the test method is called. This should set the currency ComboBox.Items (via the ItemsSource property)

[Asynchronous]
[TestMethod]
public void TestCurrencySelection()
{
    _target.Loaded += (s, e) =>
        {
            // Set the currency list explicitly
            _viewModel.IsoCurrenciesList = _currencies;

            var currencyCombo = GetUIElement<ComboBox>("cmbCurrency");
            // This assert fails as Items.Count == 0
            CollectionAssert.AreEquivalent(currencyCombo.Items, _currencies, "Failed to data-bind currencies.");

            EnqueueTestComplete();
        };

    TestPanel.Children.Add(_target);
}

I’ve followed the guidelines on Jeremy Likeness’s blog but I can’t get the bindings test to pass.

I’ve tried testing the bindings of other properties – simple strings, booleans and integers but the changes made at either end aren’t reflected to the other.

The only thing I can think of is that there is another step I need to do after adding the view to the TestPanel to “activate” the bindings, but I’ve no idea what it could be.

UPDATE

I should point out that the code works fine in the actual application. Based on the comments (particularly those from Adam Sills) it looks like the problem lies in the code I haven’t posted – i.e. it’s something in the way we’ve structured the XAML or there’s a difference in the way we set the DataContext. At least I can concentrate my efforts in (hopefully) the right area.

It appears that the position of the control in the view does matter. The page XAML is something like this:

<Grid x:Name="LayoutRoot">
    <VisualStateManager.VisualStateGroups>
        ...
    </VisualStateManager.VisualStateGroups>

    <toolkit:BusyIndicator x:Name="activityControl" 
                           IsBusy="{Binding IsBusy}" 
                           BusyContent="{Binding BusyContent}" >
        <Grid>
            ... The page definition including sub grids, stack panels
                and the combo box I'm testing along with other controls

            <ops:SaveConfirmation Grid.Row="1" Margin="5"
                                  x:Name="saveConfirmation"
                                  SavedState="{Binding VendorSaved, Mode=TwoWay}" />
        </Grid>
    </toolkit:BusyIndicator/>
</Grid>

The BusyIndicator is the one from the Silverlight Toolkit and SaveConfirmation is a control we’ve written.

If I test the IsBusy binding on the BusyIndicator that works as expected. However, if I test the SavedState binding on the SaveConfirmation that fails – I set the VendorSaved property to true in the test but when I get the control the bound value is false.

var busyIndicator = GetUIElement<BusyIndicator>("activityControl");
Assert.AreEqual(busyIndicator.IsBusy, _viewModel.IsBusy, "Failed to data-bind busy indicator.");

var saveConfirmation = GetUIElement<SaveConfirmation>("saveConfirmation");
Assert.AreEqual(saveConfirmation.SavedState, _viewModel.VendorSaved, "Failed to data-bind saved state");

So the first test passes, but the second fails.

What do I need to do to ensure that the bindings of elements all the way down the tree are set up?

Answer 1

You’ve included the XAML for your ComboBox, but not the rest of your page. In your test you have GetUIElement<Grid>("LayoutRoot").DataContext = _viewModel;. In the example you’re following, he defines:

<Grid x:Uid="LayoutRoot" x:Name="LayoutRoot" Background="White"
    DataContext="{Binding Source={StaticResource VMLocator},Path=Cascadia}">

and then the controls on which he’s testing the bindings are nested directly inside that grid. Is your page setup the same way?