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

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

xamarin combobox xamarin.forms uwp

Xamarin Forms UWP-如何隐藏或更改选择器/组合框下拉箭头的颜色,xamarin,combobox,xamarin.forms,uwp,xamarin.uwp,Xamarin,Combobox,Xamarin.forms,Uwp,Xamarin.uwp,我现在正在为UWP开发一个Xamarin.Forms项目，我正在为选择器使用一个自定义渲染器。实际上，我将选择器覆盖在标签和图标的顶部，这样当用户单击标签/图标时，它就会打开选择器。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不可见，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），还是干脆将其全部去掉去除文本和背景色非常简单，如下所示： var transparent = Windows.UI.Co

我现在正在为UWP开发一个Xamarin.Forms项目，我正在为选择器使用一个自定义渲染器。实际上，我将选择器覆盖在标签和图标的顶部，这样当用户单击标签/图标时，它就会打开选择器。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不可见，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），还是干脆将其全部去掉

去除文本和背景色非常简单，如下所示：

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

我知道该控件是一个

FormsComboBox VisualElementRender.Control

，并且我尝试在Visual Studio中扫描控件的所有属性。

对于自定义渲染，的相应本机控件位于UWP中。看见因此，对于要更改的下拉箭头，它实际上是

组合框

控件模板内的

下拉图示符

元素。通过将

可见性

属性设置为

折叠

，可以复制默认值并将

下拉图示符更新为不可见。例如：
渲染：
public class MyPickerRenderer : PickerRenderer
{      
   protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
   {
       base.OnElementChanged(e);     
       Control.Style=(Windows.UI.Xaml.Style)App.Current.Resources["pickerstyle"]; 
   }
}

这很好-正是我想要的…*然而*，我们在为项目使用代码，而不是XAML，当我将上述代码（从
）添加到App.XAML时（事实上，我正在为UWP项目而不是PCL将其添加到App.XAML中-不确定您的PCL中是否可以同时包含App.cs和App.XAML），我得到了一个关于“pickerstyle”样式的异常，说“找不到具有给定密钥的资源。”
。我找到了答案！请将x:Name=“pickerstyle”
更新为x:Key=“pickerstyle”——这就是问题所在。一旦更新，我可以接受这个答案。
<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>