覆蓋默認 ComboBoxItem colors

Question

This works to override ComboBoxItem background colors in a Xamarin Forms WPF app, but isn't very elegant because I'm having to apply templates manually to ComboBoxItems in a custom renderer:

Application.Resources 中的 App.xaml：

    <ControlTemplate TargetType="{x:Type ComboBoxItem}" x:Key="CustomComboBoxItem">
        <Border BorderThickness="{TemplateBinding Border.BorderThickness}" Padding="{TemplateBinding Control.Padding}" BorderBrush="{TemplateBinding Border.BorderBrush}" Background="{TemplateBinding Panel.Background}" Name="Bd" SnapsToDevicePixels="True">
            <ContentPresenter Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding Control.VerticalContentAlignment}" SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
        </Border>
        <ControlTemplate.Triggers>
              ... All the regular triggers here override with new colors ...
        </ControlTemplate.Triggers>
    </ControlTemplate>

    <Style TargetType="{x:Type ComboBoxItem}">
        <Setter Property='OverridesDefaultStyle' Value='True'/>
        <Setter Property="Template" Value="{StaticResource CustomComboBoxItem}">
        </Setter>
    </Style>

在自定義 PickerRenderer 中：

    protected override void UpdateNativeWidget()
    {
        base.UpdateNativeWidget();
        var c = Control;
        if (p == null)
        {
            template = System.Windows.Application.Current.Resources["CustomComboBoxItem"] as System.Windows.Controls.ControlTemplate;
            ItemsPresenter presenter = GetVisualChild<ItemsPresenter>(c);
            Popup p = VisualTreeHelper.GetChild(VisualTreeHelper.GetChild(c, 0), 0) as Popup;
            var a = (((((p.Child) as Decorator).Child as Border).Child as ScrollViewer).Content as System.Windows.Controls.Grid).Children;
            presenter = a[1] as ItemsPresenter;
            this.p = presenter;
            this.p.Loaded += Presenter_Loaded;
        }
    }

    ItemsPresenter p;
    ComboBoxItem[] items;
    System.Windows.Controls.ControlTemplate template;

    private void Presenter_Loaded(object sender, RoutedEventArgs e)
    {
        items = new ComboBoxItem[Control.ItemContainerGenerator.Items.Count];
        for(int i=0;i<items.Length;i++)
        {
            items[i] = Control.ItemContainerGenerator.ContainerFromIndex(i) as ComboBoxItem;
            if (template != null)
            {
                items[i].Template = template;
            }
        }
    }

我不能執行以下操作，否則我會得到以下異常：

ArgumentException：已添加項目。 字典中的鍵：'System.Windows.Controls.ComboBoxItem' 添加鍵：'System.Windows.Controls.ComboBoxItem'

    <ControlTemplate TargetType="{x:Type ComboBoxItem}" x:Key="{x:Type ComboBoxItem}">
    </ControlTemplate>

或者這個，默認值不會被覆蓋：

    <ControlTemplate TargetType="{x:Type ComboBoxItem}" x:Key="CustomComboBoxItem">
    </ControlTemplate>

    <Style TargetType="{x:Type ComboBoxItem}" x:Key="{x:Type ComboBoxItem}">
        <Setter Property='OverridesDefaultStyle' Value='True'/>
        <Setter Property="Template" Value="{StaticResource CustomComboBoxItem}">
        </Setter>
    </Style>

有沒有更簡單、更優雅的方式來做我想做的事情？

Answer 1

如果您想將整個應用程序中的默認comBoxItem 模板設置為customComboxItem。 您只需將樣式資源放在 app.xaml 中。

<Application.Resources>
<Style TargetType="{x:Type ComboBoxItem}" x:Key="{x:Type ComboBoxItem}">
    <Setter Property='OverridesDefaultStyle' Value='True'/>
    <Setter Property="Template" Value="{StaticResource CustomComboBoxItem}">
    </Setter>
</Style>
</Application.Resources>