How to resize the dropdown list of the ComboBox in UWP?

Question

Hello guys,

I have such a requirement. I need to set a fixed size for the combobox. It's easy to achieve it by setting the width and height. But now, I also need to set a fixed size for the dropdownList(Popup) of the combobox. With my tests, it's impossible. I tried to edit its style, it didnot work.

Is it possible to resize the dropdownlist of the combobox?

Best Regards,
Xavier

Answer 1

Hello,

Welcome to Microsoft Q&A.

The width of the combo box's drop-down list is determined by the max-width of a items, and the overall height is determined by ComboBox.MaxDropDownHeight.

Here is a example：

xaml

<Grid>
    <ComboBox x:Name="TestComboBox" MaxDropDownHeight="200"
              ItemsSource="{x:Bind TestCollection}">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding}" TextTrimming="CharacterEllipsis"
                           Width="150"/>
            </DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>
</Grid>

xaml.cs

public ObservableCollection<string> TestCollection = new ObservableCollection<string>();
public TestPage()
{
    this.InitializeComponent();
    for (int i = 0; i < 1000; i++)
    {
        TestCollection.Add(i.ToString());
    }
}

In this way, the size of the drop-down list can be limited to 150x200.

---

Update

The size of the ComboBox drop-down list will change based on the size of the internal elements, but it cannot be less than the value of the established ComboBox.Width.

In ComboBox, there is a property is TemplateSettings, this property is read-only, and this property represents some style properties when ComboBox is created, including DropDownContentMinWidth and DropDownOpenedHeight, etc., they are all read-only.

This means that these properties will be assigned and created internally after the ComboBox is instantiated, and currently cannot be modified from the outside.

So if you create a ComboBox with a width of 300, the minimum width of the drop-down list is 300. However, currently the maximum height can be modified by ComboBox.MaxDropDownHeight

Thanks.