Xamarin.Forms UWP - 如何隐藏或更改选择器/组合框下拉箭头的颜色

Question

我现在正在为 UWP 开发一个 Xamarin.Forms 项目，我正在使用 Pickers 的自定义渲染器。我实际上是将选择器覆盖在标签和图标之上，这样当用户单击 label/icon 时，它会打开选择器。为了实现这一点，我基本上将选择器上的所有内容都设置为透明——边框、文本和背景。选择器仍然可以正常工作，并且所有选择器元素都是不可见的，除了选择器箭头仍然可见。我如何影响选择器箭头的颜色（以使其透明），或者完全摆脱它？

去除文本和背景颜色非常简单：

var transparent = Windows.UI.Color.FromArgb(0, 0, 0, 0);
Control.Foreground = new SolidColorBrush(transparent);
Control.Background = new SolidColorBrush(transparent);

但我不知道如何影响下拉箭头。

我知道控件是 FormsComboBox VisualElementRender<Picker, FormsComboBox>.Control，我已经尝试扫描 Visual Studio 中控件的所有属性。

Answer 1

对于自定义渲染，Picker is ComboBox in UWP . See Renderer Base Classes and Native Controls. So that for the drop down arrow you want to change , which is actually the DropDownGlyph element inside the control template of Combobox. You could copy the default ComboBox styles and templates 的相应原生控件并通过将 Visibility 属性设置为 Collapsed 将 DropDownGlyph 更新为不可见。例如：

渲染图：

public class MyPickerRenderer : PickerRenderer
{      
   protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
   {
       base.OnElementChanged(e);     
       Control.Style=(Windows.UI.Xaml.Style)App.Current.Resources["pickerstyle"]; 
   }
}

App.xaml中的样式

<Application
    x:Class="PickerDemo.UWP.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:PickerDemo.UWP"
    RequestedTheme="Light">
    <Application.Resources>
        <Style x:Key="pickerstyle" TargetType="ComboBox">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ComboBox">
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto" />
                                <RowDefinition Height="*" />
                            </Grid.RowDefinitions>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="*" />
                                <ColumnDefinition Width="32" />
                            </Grid.ColumnDefinitions>
                            <ContentPresenter
                                x:Name="HeaderContentPresenter"
                                Margin="{ThemeResource ComboBoxHeaderThemeMargin}"
                                x:DeferLoadStrategy="Lazy"
                                Content="{TemplateBinding Header}"
                                ContentTemplate="{TemplateBinding HeaderTemplate}"
                                FlowDirection="{TemplateBinding FlowDirection}"
                                FontWeight="{ThemeResource ComboBoxHeaderThemeFontWeight}"
                                Visibility="Collapsed" />
                            <Border
                                x:Name="Background"
                                Grid.Row="1"
                                Grid.ColumnSpan="2"
                                Background="{TemplateBinding Background}"
                                BorderBrush="{TemplateBinding BorderBrush}"
                                BorderThickness="{TemplateBinding BorderThickness}" />
                            <Border
                                x:Name="HighlightBackground"
                                Grid.Row="1"
                                Grid.ColumnSpan="2"
                                Background="{ThemeResource SystemControlHighlightListAccentLowBrush}"
                                BorderBrush="{ThemeResource SystemControlHighlightBaseMediumLowBrush}"
                                BorderThickness="{TemplateBinding BorderThickness}"
                                Opacity="0" />
                            <ContentPresenter
                                x:Name="ContentPresenter"
                                Grid.Row="1"
                                Margin="{TemplateBinding Padding}"
                                HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
                                <TextBlock
                                    x:Name="PlaceholderTextBlock"
                                    Foreground="{ThemeResource SystemControlPageTextBaseHighBrush}"
                                    Text="{TemplateBinding PlaceholderText}" />
                            </ContentPresenter>
                            <FontIcon
                                x:Name="DropDownGlyph"
                                Grid.Row="1"
                                Grid.Column="1"
                                Margin="0,10,10,10"
                                HorizontalAlignment="Right"
                                VerticalAlignment="Center"
                                AutomationProperties.AccessibilityView="Raw"
                                FontFamily="{ThemeResource SymbolThemeFontFamily}"
                                FontSize="12"
                                Foreground="{ThemeResource SystemControlForegroundBaseMediumHighBrush}"
                                Glyph="&#xE0E5;"
                                IsHitTestVisible="False"
                                Visibility="Collapsed" />
                            <Popup x:Name="Popup">
                                <Border
                                    x:Name="PopupBorder"
                                    Margin="0,-1,0,-1"
                                    HorizontalAlignment="Stretch"
                                    Background="{ThemeResource SystemControlBackgroundChromeMediumLowBrush}"
                                    BorderBrush="{ThemeResource SystemControlForegroundChromeHighBrush}"
                                    BorderThickness="{ThemeResource ComboBoxDropdownBorderThickness}">
                                    <ScrollViewer
                                        x:Name="ScrollViewer"
                                        MinWidth="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.DropDownContentMinWidth}"
                                        AutomationProperties.AccessibilityView="Raw"
                                        BringIntoViewOnFocusChange="{TemplateBinding ScrollViewer.BringIntoViewOnFocusChange}"
                                        Foreground="{ThemeResource SystemControlForegroundBaseHighBrush}"
                                        HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}"
                                        HorizontalScrollMode="{TemplateBinding ScrollViewer.HorizontalScrollMode}"
                                        IsDeferredScrollingEnabled="{TemplateBinding ScrollViewer.IsDeferredScrollingEnabled}"
                                        IsHorizontalRailEnabled="{TemplateBinding ScrollViewer.IsHorizontalRailEnabled}"
                                        IsVerticalRailEnabled="{TemplateBinding ScrollViewer.IsVerticalRailEnabled}"
                                        VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}"
                                        VerticalScrollMode="{TemplateBinding ScrollViewer.VerticalScrollMode}"
                                        VerticalSnapPointsAlignment="Near"
                                        VerticalSnapPointsType="OptionalSingle"
                                        ZoomMode="Disabled">
                                        <ItemsPresenter Margin="{ThemeResource ComboBoxDropdownContentMargin}" />
                                    </ScrollViewer>
                                </Border>
                            </Popup>
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="CommonStates">
                                    <VisualState x:Name="Normal" />
                                    <VisualState x:Name="PointerOver">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Background" Storyboard.TargetProperty="Background">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlPageBackgroundAltMediumBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Background" Storyboard.TargetProperty="BorderBrush">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightBaseMediumBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Pressed">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Background" Storyboard.TargetProperty="Background">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundListMediumBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Background" Storyboard.TargetProperty="BorderBrush">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightBaseMediumLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Disabled">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Background" Storyboard.TargetProperty="Background">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlBackgroundBaseLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="Background" Storyboard.TargetProperty="BorderBrush">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="HeaderContentPresenter" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseMediumLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseMediumLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PlaceholderTextBlock" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseMediumLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="DropDownGlyph" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlDisabledBaseMediumLowBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                                <VisualStateGroup x:Name="FocusStates">
                                    <VisualState x:Name="Focused">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="HighlightBackground" Storyboard.TargetProperty="BorderBrush">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightTransparentBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <DoubleAnimation
                                                Storyboard.TargetName="HighlightBackground"
                                                Storyboard.TargetProperty="Opacity"
                                                To="1"
                                                Duration="0" />
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltBaseHighBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PlaceholderTextBlock" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltBaseHighBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="DropDownGlyph" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltBaseMediumHighBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="FocusedPressed">
                                        <Storyboard>
                                            <DoubleAnimation
                                                Storyboard.TargetName="HighlightBackground"
                                                Storyboard.TargetProperty="Opacity"
                                                To="1"
                                                Duration="0" />
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ContentPresenter" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltBaseHighBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="PlaceholderTextBlock" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltBaseHighBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames Storyboard.TargetName="DropDownGlyph" Storyboard.TargetProperty="Foreground">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource SystemControlHighlightAltBaseMediumHighBrush}" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Unfocused" />
                                    <VisualState x:Name="PointerFocused" />
                                    <VisualState x:Name="FocusedDropDown">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames
                                                Storyboard.TargetName="PopupBorder"
                                                Storyboard.TargetProperty="Visibility"
                                                Duration="0">
                                                <DiscreteObjectKeyFrame KeyTime="0">
                                                    <DiscreteObjectKeyFrame.Value>
                                                        <Visibility>Visible</Visibility>
                                                    </DiscreteObjectKeyFrame.Value>
                                                </DiscreteObjectKeyFrame>
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                                <VisualStateGroup x:Name="DropDownStates">
                                    <VisualState x:Name="Opened">
                                        <Storyboard>
                                            <SplitOpenThemeAnimation
                                                ClosedTargetName="ContentPresenter"
                                                OffsetFromCenter="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.DropDownOffset}"
                                                OpenedLength="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.DropDownOpenedHeight}"
                                                OpenedTargetName="PopupBorder" />
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Closed">
                                        <Storyboard>
                                            <SplitCloseThemeAnimation
                                                ClosedTargetName="ContentPresenter"
                                                OffsetFromCenter="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.DropDownOffset}"
                                                OpenedLength="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TemplateSettings.DropDownOpenedHeight}"
                                                OpenedTargetName="PopupBorder" />
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Application.Resources>
</Application>

Xamarin.Forms UWP - 如何隐藏或更改选择器/组合框下拉箭头的颜色

Xamarin.Forms UWP - How to hide or change color of Picker / ComboBox dropdown arrow

combobox

xamarin

xamarin.forms

uwp

xamarin.uwp