不一致的Silverlight 4 ComboBox下拉显示
我有一个Silverlight 4应用程序，在表单底部附近有一个ComboBox。 Dropdown中可以有大约30到100个项目。
当我第一次打开ComboBox时，没有SelectedItem，Dropdown向上打开，它可以看到大约23个条目;只要我没有选择项目，每次重新打开Dropdown时它都会继续这种行为。一旦我选择了一个项目，每次我打开ComboBox后，它总是向下打开Dropdown，并且只显示3个条目。
我猜测Dropdown仅限于3项，因为这是在我的屏幕上最大化时窗口的下限。
如果以前选择了某个项目，我如何让它显示更多项目？
以下是一个示例Silverlight应用程序，用于演示浏览器内外的行为。
MainPage.xaml中：
<UserControl x:Class="ComboBox_Test.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="650" d:DesignWidth="1024">
<Grid x:Name="LayoutRoot" Background="LightSteelBlue" Loaded="MainPage_OnLoaded">
<Grid.RowDefinitions>
<RowDefinition Height="3*" MinHeight="25" MaxHeight="25" />
<RowDefinition Height="35*" MinHeight="200" />
<RowDefinition Height="10*" MinHeight="70" MaxHeight="70" />
<RowDefinition Height="30*" MinHeight="230" MaxHeight="230" />
<RowDefinition Height="*" MinHeight="10" MaxHeight="30" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="12" />
<ColumnDefinition Width="150" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="12" />
</Grid.ColumnDefinitions>
<TextBlock Name="lblData" Text="Data:" Grid.Row="1" Grid.Column="1" />
<TextBox x:Name="txtData" Grid.Row="1" Grid.Column="2" VerticalScrollBarVisibility="Auto"
HorizontalScrollBarVisibility="Auto" />
<StackPanel x:Name="AccessPanel" Orientation="Vertical" HorizontalAlignment="Left" Margin="5"
Grid.Row="3" Grid.Column="2" Visibility="Visible">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="75" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<StackPanel x:Name="CreationPanel" Orientation="Vertical" Grid.Row="1">
<Grid x:Name="CreationRoot">
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<StackPanel x:Name="TypesPanel" Orientation="Horizontal" Grid.Row="1" Grid.Column="1"
Margin="0 5 0 5">
<Grid x:Name="TypesRoot">
<Grid.RowDefinitions>
<RowDefinition Height="25" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="220" />
<ColumnDefinition Width="220" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Text="Types" FontFamily="Arial" FontSize="12" FontWeight="Bold"
Grid.Row="0" Grid.Column="0" />
<ComboBox x:Name="cboTypes" Width="220" Height="30" Grid.Row="1" Grid.Column="0"
IsEnabled="True"
SelectionChanged="cboTypes_SelectionChanged">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name, Mode=OneWay}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
</StackPanel>
</Grid>
</StackPanel>
</Grid>
</StackPanel>
</Grid>
</UserControl>
MainPage.xaml.cs中：
using System;
using System.Windows;
using System.Windows.Controls;
namespace ComboBox_Test
{
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
}
private void UpdateDataText(DataTypeDesc oData)
{
txtData.Text = String.Format("{0}\n\t{1}", oData.Name, oData.Desc);
}
private void MainPage_OnLoaded(object sender, RoutedEventArgs e)
{
object[] aDataTypeDescs = new object[]
{
new DataTypeDesc() {Name = "Boolean", Desc = "A Boolean value"}
, new DataTypeDesc() {Name = "Byte", Desc = "An 8-bit unsigned integer"}
, new DataTypeDesc() {Name = "Char", Desc = "A Unicode character"}
, new DataTypeDesc() {Name = "Double", Desc = "A double-precision floating-point number"}
, new DataTypeDesc() {Name = "float", Desc = "A single-precision floating-point number"}
, new DataTypeDesc() {Name = "Int16", Desc = "A 16-bit signed integer"}
, new DataTypeDesc() {Name = "Int32", Desc = "A 32-bit signed integer"}
, new DataTypeDesc() {Name = "Int64", Desc = "A 64-bit signed integer"}
, new DataTypeDesc() {Name = "SByte", Desc = "An 8-bit signed integer"}
, new DataTypeDesc() {Name = "UInt16", Desc = "A 16-bit unsigned integer"}
, new DataTypeDesc() {Name = "UInt32", Desc = "A 32-bit unsigned integer"}
, new DataTypeDesc() {Name = "UInt64", Desc = "A 64-bit unsigned integer"}
, new DataTypeDesc() {Name = "A", Desc = "The letter A in the alphabet"}
, new DataTypeDesc() {Name = "B", Desc = "The letter B in the alphabet"}
, new DataTypeDesc() {Name = "C", Desc = "The letter C in the alphabet"}
, new DataTypeDesc() {Name = "D", Desc = "The letter D in the alphabet"}
, new DataTypeDesc() {Name = "E", Desc = "The letter E in the alphabet"}
, new DataTypeDesc() {Name = "F", Desc = "The letter F in the alphabet"}
, new DataTypeDesc() {Name = "G", Desc = "The letter G in the alphabet"}
, new DataTypeDesc() {Name = "H", Desc = "The letter H in the alphabet"}
, new DataTypeDesc() {Name = "I", Desc = "The letter I in the alphabet"}
, new DataTypeDesc() {Name = "J", Desc = "The letter J in the alphabet"}
, new DataTypeDesc() {Name = "K", Desc = "The letter K in the alphabet"}
, new DataTypeDesc() {Name = "L", Desc = "The letter L in the alphabet"}
, new DataTypeDesc() {Name = "M", Desc = "The letter M in the alphabet"}
, new DataTypeDesc() {Name = "N", Desc = "The letter N in the alphabet"}
, new DataTypeDesc() {Name = "O", Desc = "The letter O in the alphabet"}
, new DataTypeDesc() {Name = "P", Desc = "The letter P in the alphabet"}
, new DataTypeDesc() {Name = "Q", Desc = "The letter Q in the alphabet"}
, new DataTypeDesc() {Name = "R", Desc = "The letter R in the alphabet"}
, new DataTypeDesc() {Name = "S", Desc = "The letter S in the alphabet"}
, new DataTypeDesc() {Name = "T", Desc = "The letter T in the alphabet"}
, new DataTypeDesc() {Name = "U", Desc = "The letter U in the alphabet"}
, new DataTypeDesc() {Name = "V", Desc = "The letter V in the alphabet"}
, new DataTypeDesc() {Name = "W", Desc = "The letter W in the alphabet"}
, new DataTypeDesc() {Name = "X", Desc = "The letter X in the alphabet"}
, new DataTypeDesc() {Name = "Y", Desc = "The letter Y in the alphabet"}
, new DataTypeDesc() {Name = "Z", Desc = "The letter Z in the alphabet"}
};
cboTypes.ItemsSource = aDataTypeDescs;
}
private void cboTypes_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
DataTypeDesc oDesc = (DataTypeDesc)(cboTypes.SelectedItem);
if (oDesc != null)
UpdateDataText(oDesc);
}
}
}
DataTypeDesc.cs：
using System;
namespace ComboBox_Test
{
public class DataTypeDesc
{
public String Name { get; set; }
public String Desc { get; set; }
}
}
3 个答案:
答案 0 :(得分：3)
您需要编辑基本的ComboBox模板并更改名为Popup的元素的大小。在此示例中，它已设置为100高，现在显示相同的固定高度弹出窗口，无论是初始列表还是选择后：
*注意：我使用Expression blend来编辑基本模板的副本（非常详细）。由于元素部分被命名为“Popup”，您理论上可以编写代码以在可视化树中查找该部分并以此方式修改height属性。
以下更改页面的来源：
<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:System="clr-namespace:System;assembly=mscorlib" x:Class="ComboBox_Test.MainPage"
d:DesignHeight="650" d:DesignWidth="1024" mc:Ignorable="d">
<UserControl.Resources>
<ControlTemplate x:Key="ValidationToolTipTemplate">
<Grid x:Name="Root" Margin="5,0" Opacity="0" RenderTransformOrigin="0,0">
<Grid.RenderTransform>
<TranslateTransform x:Name="xform" X="-25"/>
</Grid.RenderTransform>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="OpenStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
<VisualTransition GeneratedDuration="0:0:0.2" To="Open">
<Storyboard>
<DoubleAnimation Duration="0:0:0.2" To="0" Storyboard.TargetProperty="X" Storyboard.TargetName="xform">
<DoubleAnimation.EasingFunction>
<BackEase Amplitude=".3" EasingMode="EaseOut"/>
</DoubleAnimation.EasingFunction>
</DoubleAnimation>
<DoubleAnimation Duration="0:0:0.2" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Root"/>
</Storyboard>
</VisualTransition>
</VisualStateGroup.Transitions>
<VisualState x:Name="Closed">
<Storyboard>
<DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Root"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Open">
<Storyboard>
<DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="X" Storyboard.TargetName="xform"/>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Root"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Border Background="#052A2E31" CornerRadius="5" Margin="4,4,-4,-4"/>
<Border Background="#152A2E31" CornerRadius="4" Margin="3,3,-3,-3"/>
<Border Background="#252A2E31" CornerRadius="3" Margin="2,2,-2,-2"/>
<Border Background="#352A2E31" CornerRadius="2" Margin="1,1,-1,-1"/>
<Border Background="#FFDC000C" CornerRadius="2"/>
<Border CornerRadius="2">
<TextBlock Foreground="White" MaxWidth="250" Margin="8,4,8,4" TextWrapping="Wrap" Text="{Binding (Validation.Errors)[0].ErrorContent}" UseLayoutRounding="false"/>
</Border>
</Grid>
</ControlTemplate>
<Style x:Key="ComboBoxStyle1" TargetType="ComboBox">
<Setter Property="Padding" Value="6,2,25,2"/>
<Setter Property="Background" Value="#FF1F3B53"/>
<Setter Property="HorizontalContentAlignment" Value="Left"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="TabNavigation" Value="Once"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="BorderBrush">
<Setter.Value>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FFA3AEB9" Offset="0"/>
<GradientStop Color="#FF8399A9" Offset="0.375"/>
<GradientStop Color="#FF718597" Offset="0.375"/>
<GradientStop Color="#FF617584" Offset="1"/>
</LinearGradientBrush>
</Setter.Value>
</Setter>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid>
<Grid.Resources>
<Style x:Name="comboToggleStyle" TargetType="ToggleButton">
<Setter Property="Foreground" Value="#FF333333"/>
<Setter Property="Background" Value="#FF1F3B53"/>
<Setter Property="BorderBrush">
<Setter.Value>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FFA3AEB9" Offset="0"/>
<GradientStop Color="#FF8399A9" Offset="0.375"/>
<GradientStop Color="#FF718597" Offset="0.375"/>
<GradientStop Color="#FF617584" Offset="1"/>
</LinearGradientBrush>
</Setter.Value>
</Setter>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Padding" Value="3"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Grid>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualState x:Name="Normal"/>
<VisualState x:Name="MouseOver">
<Storyboard>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="BackgroundOverlay"/>
<ColorAnimation Duration="0" To="#7FFFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
<ColorAnimation Duration="0" To="#CCFFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
<ColorAnimation Duration="0" To="#F2FFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Pressed">
<Storyboard>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="BackgroundOverlay2"/>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="Highlight"/>
<ColorAnimation Duration="0" To="#E5FFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
<ColorAnimation Duration="0" To="#BCFFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
<ColorAnimation Duration="0" To="#6BFFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
<ColorAnimation Duration="0" To="#F2FFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Disabled"/>
</VisualStateGroup>
<VisualStateGroup x:Name="CheckStates">
<VisualState x:Name="Checked">
<Storyboard>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="BackgroundOverlay3"/>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="Highlight"/>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="BackgroundGradient2"/>
<ColorAnimation Duration="0" To="#E5FFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient2"/>
<ColorAnimation Duration="0" To="#BCFFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient2"/>
<ColorAnimation Duration="0" To="#6BFFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient2"/>
<ColorAnimation Duration="0" To="#F2FFFFFF" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)" Storyboard.TargetName="BackgroundGradient2"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Unchecked"/>
</VisualStateGroup>
<VisualStateGroup x:Name="FocusStates">
<VisualState x:Name="Focused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Visibility" Storyboard.TargetName="FocusVisualElement">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Unfocused"/>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Rectangle x:Name="Background" Fill="{TemplateBinding Background}" RadiusY="3" RadiusX="3" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="{TemplateBinding BorderThickness}"/>
<Rectangle x:Name="BackgroundOverlay" Fill="#FF448DCA" Opacity="0" RadiusY="3" RadiusX="3" Stroke="#00000000" StrokeThickness="{TemplateBinding BorderThickness}"/>
<Rectangle x:Name="BackgroundOverlay2" Fill="#FF448DCA" Opacity="0" RadiusY="3" RadiusX="3" Stroke="#00000000" StrokeThickness="{TemplateBinding BorderThickness}"/>
<Rectangle x:Name="BackgroundGradient" Margin="{TemplateBinding BorderThickness}" RadiusY="2" RadiusX="2" Stroke="#FFFFFFFF" StrokeThickness="1">
<Rectangle.Fill>
<LinearGradientBrush EndPoint=".7,1" StartPoint=".7,0">
<GradientStop Color="#FFFFFFFF" Offset="0"/>
<GradientStop Color="#F9FFFFFF" Offset="0.375"/>
<GradientStop Color="#E5FFFFFF" Offset="0.625"/>
<GradientStop Color="#C6FFFFFF" Offset="1"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle x:Name="BackgroundOverlay3" Fill="#FF448DCA" Opacity="0" RadiusY="3" RadiusX="3" Stroke="#00000000" StrokeThickness="{TemplateBinding BorderThickness}"/>
<Rectangle x:Name="BackgroundGradient2" Margin="{TemplateBinding BorderThickness}" Opacity="0" RadiusY="2" RadiusX="2" Stroke="#FFFFFFFF" StrokeThickness="1">
<Rectangle.Fill>
<LinearGradientBrush EndPoint=".7,1" StartPoint=".7,0">
<GradientStop Color="#FFFFFFFF" Offset="0"/>
<GradientStop Color="#F9FFFFFF" Offset="0.375"/>
<GradientStop Color="#E5FFFFFF" Offset="0.625"/>
<GradientStop Color="#C6FFFFFF" Offset="1"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle x:Name="Highlight" IsHitTestVisible="false" Margin="{TemplateBinding BorderThickness}" Opacity="0" RadiusY="2" RadiusX="2" Stroke="#FF6DBDD1" StrokeThickness="1"/>
<ContentPresenter x:Name="contentPresenter" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
<Rectangle x:Name="FocusVisualElement" IsHitTestVisible="false" Margin="1" RadiusY="3.5" RadiusX="3.5" Stroke="#FF6DBDD1" StrokeThickness="1" Visibility="Collapsed"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Grid.Resources>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualState x:Name="Normal"/>
<VisualState x:Name="MouseOver"/>
<VisualState x:Name="Disabled">
<Storyboard>
<DoubleAnimation Duration="00:00:00" To=".55" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="DisabledVisualElement"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="FocusStates">
<VisualState x:Name="Focused">
<Storyboard>
<DoubleAnimation Duration="00:00:00" To="1" Storyboard.TargetProperty="(UIElement.Opacity)" Storyboard.TargetName="FocusVisualElement"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Unfocused"/>
<VisualState x:Name="FocusedDropDown">
<Storyboard>
<ObjectAnimationUsingKeyFrames Duration="00:00:00" Storyboard.TargetProperty="(UIElement.Visibility)" Storyboard.TargetName="PopupBorder">
<DiscreteObjectKeyFrame KeyTime="00:00:00">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="ValidationStates">
<VisualState x:Name="Valid"/>
<VisualState x:Name="InvalidUnfocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Visibility" Storyboard.TargetName="ValidationErrorElement">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="InvalidFocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Visibility" Storyboard.TargetName="ValidationErrorElement">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="IsOpen" Storyboard.TargetName="validationTooltip">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<System:Boolean>True</System:Boolean>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Border x:Name="ContentPresenterBorder">
<Grid>
<ToggleButton x:Name="DropDownToggle" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" HorizontalAlignment="Stretch" HorizontalContentAlignment="Right" Margin="0" Style="{StaticResource comboToggleStyle}" VerticalAlignment="Stretch">
<Path x:Name="BtnArrow" Data="F1 M 301.14,-189.041L 311.57,-189.041L 306.355,-182.942L 301.14,-189.041 Z " HorizontalAlignment="Right" Height="4" Margin="0,0,6,0" Stretch="Uniform" Width="8">
<Path.Fill>
<SolidColorBrush x:Name="BtnArrowColor" Color="#FF333333"/>
</Path.Fill>
</Path>
</ToggleButton>
<ContentPresenter x:Name="ContentPresenter" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
<TextBlock Text=" "/>
</ContentPresenter>
</Grid>
</Border>
<Rectangle x:Name="DisabledVisualElement" Fill="White" IsHitTestVisible="false" Opacity="0" RadiusY="3" RadiusX="3"/>
<Rectangle x:Name="FocusVisualElement" IsHitTestVisible="false" Margin="1" Opacity="0" RadiusY="2" RadiusX="2" Stroke="#FF6DBDD1" StrokeThickness="1"/>
<Border x:Name="ValidationErrorElement" BorderBrush="#FFDB000C" BorderThickness="1" CornerRadius="1" Visibility="Collapsed">
<ToolTipService.ToolTip>
<ToolTip x:Name="validationTooltip" DataContext="{Binding RelativeSource={RelativeSource TemplatedParent}}" Placement="Right" PlacementTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}" Template="{StaticResource ValidationToolTipTemplate}">
<ToolTip.Triggers>
<EventTrigger RoutedEvent="Canvas.Loaded">
<BeginStoryboard>
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="IsHitTestVisible" Storyboard.TargetName="validationTooltip">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<System:Boolean>true</System:Boolean>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</ToolTip.Triggers>
</ToolTip>
</ToolTipService.ToolTip>
<Grid Background="Transparent" HorizontalAlignment="Right" Height="12" Margin="1,-4,-4,0" VerticalAlignment="Top" Width="12">
<Path Data="M 1,0 L6,0 A 2,2 90 0 1 8,2 L8,7 z" Fill="#FFDC000C" Margin="1,3,0,0"/>
<Path Data="M 0,0 L2,0 L 8,6 L8,8" Fill="#ffffff" Margin="1,3,0,0"/>
</Grid>
</Border>
<Popup x:Name="Popup">
<Border x:Name="PopupBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="3" HorizontalAlignment="Stretch" Height="100">
<Border.Background>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FFFFFFFF" Offset="0"/>
<GradientStop Color="#FFFEFEFE" Offset="1"/>
</LinearGradientBrush>
</Border.Background>
<ScrollViewer x:Name="ScrollViewer" BorderThickness="0" Padding="1">
<ItemsPresenter/>
</ScrollViewer>
</Border>
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</UserControl.Resources>
<Grid x:Name="LayoutRoot" Background="LightSteelBlue" Loaded="MainPage_OnLoaded">
<Grid.RowDefinitions>
<RowDefinition Height="3*" MinHeight="25" MaxHeight="25" />
<RowDefinition Height="35*" MinHeight="200" />
<RowDefinition Height="10*" MinHeight="70" MaxHeight="70" />
<RowDefinition Height="30*" MinHeight="230" MaxHeight="230" />
<RowDefinition Height="*" MinHeight="10" MaxHeight="30" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="12" />
<ColumnDefinition Width="150" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="12" />
</Grid.ColumnDefinitions>
<TextBlock x:Name="lblData" Text="Data:" Grid.Row="1" Grid.Column="1" />
<TextBox x:Name="txtData" Grid.Row="1" Grid.Column="2" VerticalScrollBarVisibility="Auto"
HorizontalScrollBarVisibility="Auto" />
<StackPanel x:Name="AccessPanel" Orientation="Vertical" HorizontalAlignment="Left" Margin="5"
Grid.Row="3" Grid.Column="2" Visibility="Visible">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="75" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<StackPanel x:Name="CreationPanel" Orientation="Vertical" Grid.Row="1">
<Grid x:Name="CreationRoot">
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<StackPanel x:Name="TypesPanel" Orientation="Horizontal" Grid.Row="1" Grid.Column="1"
Margin="0 5 0 5">
<Grid x:Name="TypesRoot">
<Grid.RowDefinitions>
<RowDefinition Height="25" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="220" />
<ColumnDefinition Width="220" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Text="Types" FontFamily="Arial" FontSize="12" FontWeight="Bold"
Grid.Row="0" Grid.Column="0" />
<ComboBox x:Name="cboTypes" Width="220" Height="30" Grid.Row="1" Grid.Column="0"
IsEnabled="True"
SelectionChanged="cboTypes_SelectionChanged" MaxDropDownHeight="600" Style="{StaticResource ComboBoxStyle1}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name, Mode=OneWay}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
</StackPanel>
</Grid>
</StackPanel>
</Grid>
</StackPanel>
</Grid>
</UserControl>
答案 1 :(得分：1)
我遇到了同样的问题（实际上是使用Silverlight 5，但仍然是相同的行为）并且发现了一个不太可能的解决方案，不涉及修改模板（在我的情况下，我不想强迫Popup拥有固定的大小和方向）。
我发现如果我使用ComboBoxItems而不是自定义对象集合填充我的ComboBox，则不会发生下拉/选择/方向问题。我真的不想这样做，因为我的原始设计是在ItemsSource，SelectedItem等上使用Binding。但是由于它修复了问题，我使用了ComboBoxItems并删除了绑定方法。
所以这里有几个快速的代码片段来说明差异 - 第一个使用自定义对象的集合并导致奇怪的行为（我的VehicleData类只是一个带有ID和Name以及其他一些属性的简单类）：
// List of Custom Objects - Results in inconsistent behavior
ObservableCollection<VehicleData> vehicleList = new ObservableCollection<VehicleData>();
for (int i = 0; i < 80; i++)
{
vehicleList.Add(new VehicleData
{
ID = i,
Name = string.Format("Vehicle {0}", i)
});
}
ComboBoxVehicles.DisplayMemberPath = "Name";
ComboBoxVehicles.ItemsSource = vehicleList;
这是一个很好的例子，无论添加了多少项以及ComboBox的定位是什么：
// List of ComboBoxItems - WORKS
List<ComboBoxItem> testValues = new List<ComboBoxItem>();
for (int i = 0; i < 80; i++)
{
testValues.Add(new ComboBoxItem
{
Content = "Item " + i,
Tag = i
});
}
ComboBoxVehicles.ItemsSource = testValues;
我知道这个问题已经得到了回答，但我想如果它帮助了其他人，我会发布这个问题。
答案 2 :(得分：0)
根据您拥有的物品数量和可用的屏幕高度，您还可以设置ScrollViewer.VerticalScrollBarVisibility="Disabled"，这会强制它向上打开，因为没有空间向下。
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