Select custom ComboBox item with UI Automation

Question

How do I select an item in a custom ComboBox with Microsoft UI Automation? I have ComboBox that looks like this:

<ComboBox AutomationProperties.AutomationId="Rm8Function"
          ItemsSource="{Binding Source={StaticResource Functions}}"
          SelectedItem="{Binding Function, UpdateSourceTrigger=PropertyChanged}">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock
                Text="{Binding Mode=OneTime, Converter={StaticResource FunctionEnumConverter}}" />
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

I.e. I have overriden the ItemTemplate with a custom DataTemplate.

However, now I am not able to select the item using the answer on selecting combobox item using ui automation:

public static void SelectComboBoxItem(this AutomationElement comboBox, string item)
{
    var expandCollapsePattern = comboBox.GetPattern<ExpandCollapsePattern>(ExpandCollapsePatternIdentifiers.Pattern);
    expandCollapsePattern.Expand();
    expandCollapsePattern.Collapse();
    var listItem = comboBox.FindFirst(TreeScope.Subtree,
        new PropertyCondition(AutomationElement.NameProperty, item));
    var selectionItemPattern = listItem.GetPattern<SelectionItemPattern>(SelectionItemPatternIdentifiers.Pattern);
    selectionItemPattern.Select();
}

public static T GetPattern<T>(this AutomationElement element, AutomationPattern pattern) where T: BasePattern
{
    try
    {
        return (T) element.GetCurrentPattern(pattern);
    }
    catch (InvalidOperationException)
    {
        element.PrintSupportedPatterns();
        throw;
    }
}

It throws an error telling me that SelectionItemPatternIdentifiers.Pattern is an unsupported pattern. It's only SynchronizedInputPatternIdentifiers.Pattern that is supported by the element it's trying to select in the ComboBox.

How should I write my DataTemplate so that it becomes selectable?

Answer 1

I re-defined my ComboBox in the following way:

<ComboBox AutomationProperties.AutomationId="Rm8Function"
          ItemsSource="{Binding Source={StaticResource Functions}}"
          SelectedItem="{Binding Function, UpdateSourceTrigger=PropertyChanged}">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock
                AutomationProperties.Name="{Binding Mode=OneTime, Converter={StaticResource FunctionEnumConverter}}"
                Text="{Binding Mode=OneTime, Converter={StaticResource FunctionEnumConverter}}" />
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

Giving the TextBlock the same AutomationProperties.Name value as its Text value.

I also updated my function that selects the ComboBox item to the following:

public static void SelectComboBoxItem(this AutomationElement comboBox, string item)
{
    var expandCollapsePattern = comboBox.GetPattern<ExpandCollapsePattern>(ExpandCollapsePatternIdentifiers.Pattern);
    expandCollapsePattern.Expand();
    expandCollapsePattern.Collapse();
    var listItem = comboBox.FindFirst(TreeScope.Subtree,
        new PropertyCondition(AutomationElement.NameProperty, item));
    var walker = TreeWalker.ControlViewWalker;
    var parent = walker.GetParent(listItem);
    while (parent != comboBox)
    {
        listItem = parent;
        parent = walker.GetParent(listItem);
    }
    var selectionItemPattern = listItem.GetPattern<SelectionItemPattern>(SelectionItemPatternIdentifiers.Pattern);
    selectionItemPattern.Select();
}

Apparently, when using a ComboBox as-is without overriding the ItemTemplate, the function above finds its immediate child which is a ListBoxItem. It's the ListBoxItem that is selectable through the SelectionItemPattern pattern. But when overriding the ItemTemplate, the function instead finds the TextBlock that is a child to the ListBoxItem. Therefore, I had to modify my function in such a way that it traverses upwards until it finds the immediate child to the ComboBox and selects it.