将组合框绑定到列表 <string> 在WPF中

Question

This is a silverlight app.

I am trying to bind a combobox to a list of strings. It will display values the I have stored in the list prior to loading the application, but I also have it so the user can add strings to the list, and these changes are not reflected in the combobox. I have confirmed the list is being updated correctly, just not the combobox.

The way the below code is currently, when I update the list at runtime then click the combobox dropdown, the entire silverlight app disappears. It doesn't throw any errors that I can see in VS, debug output, or in the browser, the browser window containing the silverlight app just goes blank.

 <UserControl x:Class="SilverlightSpeak.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"
             xmlns:local="clr-namespace:SilverlightSpeak.ViewModels"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">

    <UserControl.Resources>
        <local:MainViewModel x:Key="MainViewModel"/>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White" HorizontalAlignment="Center" VerticalAlignment="Top" DataContext="{StaticResource MainViewModel}">
        <Grid.RowDefinitions>
            <RowDefinition Height="23*"/>
            <RowDefinition Height="21*"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="193*"/>
            <ColumnDefinition Width="60*"/>
        </Grid.ColumnDefinitions>
        <Button Content="Add" Command="{Binding AddWordCommand}" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Grid.Column="1"/>
        <TextBox Text="{Binding ModelSpeaker.newWord, Mode=TwoWay}" HorizontalAlignment="Left" Height="23" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
        <ComboBox  ItemsSource="{Binding ModelSpeaker.vocab, Mode=TwoWay}"  SelectedIndex="{Binding ModelSpeaker.nextWordToSpeak, Mode=TwoWay}" HorizontalAlignment="Left" VerticalAlignment="Top" Width="120" Grid.Row="1"/>
        <Button Content="Speak" Command="{Binding SpeakWordCommand}" CommandParameter="{Binding ModelSpeaker.nextWordToSpeak}" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Grid.Row="1" Grid.Column="1" Grid.RowSpan="2"/>

    </Grid>
</UserControl>

Is there something I'm doing wrong in my xaml here? I have INotifyPropertyChanged implemented in my MainViewModel and Speaker Model class and the notifications are being sent when vocab is getting updated. I'm at a loss of how to fix this.

Thanks in advance for any help.

Answer 1

In order to get updates when a collection changes, the collection needs to implement INotifyCollectionChanged . List<T> does not implement this, but ObservableCollection<T> does, and works just like a List .

So, try changing your type from List<string> to ObservableCollection<string> .