Pantalla desplegable ComboBox de Silverlight 4 inconsistente
Tengo una aplicación Silverlight 4 con un ComboBox cerca de la parte inferior del formulario. Puede haber entre 30 y 100 elementos en el menú desplegable.
Cuando abro el ComboBox por primera vez, no hay SelectedItem, el menú desplegable se abre hacia arriba y hace visibles unas 23 entradas; continuará este comportamiento cada vez que vuelva a abrir el menú desplegable, siempre que no seleccione un elemento. Una vez que selecciono un elemento, cada vez que abro el ComboBox, siempre abre el menú desplegable hacia abajo, y solo hace visibles 3 entradas.
Supongo que el menú desplegable está limitado a 3 elementos, porque ese es el límite inferior de la ventana cuando está maximizado en mi pantalla.
¿Cómo consigo que muestre más elementos, incluso cuando un elemento ha sido seleccionado previamente?
Aquí hay un ejemplo de aplicación Silverlight que demuestra el comportamiento, tanto dentro como fuera del navegador.
MainPage.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);
}
}
}
DataTypeDesc.cs:
using System;
namespace ComboBox_Test
{
public class DataTypeDesc
{
public String Name { get; set; }
public String Desc { get; set; }
}
}