Mvvm KeyDown的实现以及TextBox绑定的属性不更新问题的解决

今天写程序的时候遇到了个问题：使用mvvm给TextBox在vm层实现KeyDown键盘事件时，TextBox绑定的vm层属性不更新。

但在TextBox下加个按钮时就更新了。这个问题困扰了我好一会，最后才想起来是更新时机没有给定，所以默认的是LostFocus，故改为PropertyChanged就好了。

<Window x:Class="TestDemo1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:cmd="http://www.galasoft.ch/mvvmlight"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        xmlns:ignore="http://www.galasoft.ch/ignore"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        Title="MVVM Light Application"
        Width="300"
        Height="300"
        DataContext="{Binding Main,
                              Source={StaticResource Locator}}"
        mc:Ignorable="d ignore">

    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Skins/MainSkin.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>

    <Grid x:Name="LayoutRoot">
        <StackPanel>
            <TextBlock Margin="0,50,0,0"
                       HorizontalAlignment="Center"
                       VerticalAlignment="Center"
                       FontWeight="Bold"
                       Foreground="Purple"
                       Text="{Binding WelcomeTitle}"
                       TextWrapping="Wrap" />
            <TextBox Margin="20" Text="{Binding MyField, UpdateSourceTrigger=PropertyChanged}">
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="KeyDown">
                        <cmd:EventToCommand Command="{Binding MyTestCommand}" />
                    </i:EventTrigger>
                </i:Interaction.Triggers>
            </TextBox>
            <Button Height="20"
                    Command="{Binding CmdBtn}"
                    Content="Button" />
        </StackPanel>
    </Grid>
</Window>

 链接：http://files.cnblogs.com/files/zhangyongheng/TestDemo1.rar