我有一个 Silverlight 4 应用程序，在窗体底部附近有一个组合框。下拉列表中可以包含大约 30 到 100 个项目。
当我第一次打开 ComboBox 时，没有 SelectedItem，Dropdown 向上打开，大约有 23 个条目可见；只要我不选择某个项目，每次我重新打开下拉菜单时，它都会继续这种行为。一旦我选择了一个项目，此后每次我打开组合框时，它总是向下打开下拉菜单，并且只显示 3 个条目。
我猜测下拉菜单仅限于 3 个项目，因为这是窗口在屏幕上最大化时的底部限制。
即使先前已选择某个项目，如何让它显示更多项目？
下面是一个示例 Silverlight 应用程序，演示了浏览器内和浏览器外的行为。
主页.xaml：
<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：
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);
}
}
}
数据类型描述.cs：
using System;
namespace ComboBox_Test
{
public class DataTypeDesc
{
public String Name { get; set; }
public String Desc { get; set; }
}
}
