您可以通过创建行为来实现这一点，如下所示:

You can achieve this by creating a behavior, like this:

public class UpperCaseAction : TriggerAction<TextBox>
{

    protected override void Invoke(object parameter)
    {
        var selectionStart = AssociatedObject.SelectionStart;
        var selectionLenght = AssociatedObject.SelectionLength;
        AssociatedObject.Text = AssociatedObject.Text.ToUpper();
        AssociatedObject.SelectionStart = selectionStart;
        AssociatedObject.SelectionLength = selectionLenght;
    }
}

然后，在您的 TextBox 中使用它，如下所示:

Then, use it in your TextBox, like this:

<Grid x:Name="LayoutRoot" Background="White">
    <TextBox TextWrapping="Wrap" VerticalAlignment="Top" Margin="10">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="TextChanged">
                <ASD_Answer009_Behaviors:UpperCaseAction/>
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </TextBox>
</Grid>

其中 i: 是

clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity

背后的代码:

System.Windows.Interactivity.EventTrigger eventTrigger = new System.Windows.Interactivity.EventTrigger("TextChanged");
eventTrigger.Actions.Add(new UpperCaseAction());   
System.Windows.Interactivity.Interaction.GetTriggers(myTextBox).Add(eventTrigger);

为了创建和使用行为，您需要下载并安装Expression Blend SDK for Silverlight 4 并添加对 System.Windows.Interactivity.dll.

In order to create and use behaviors, you need to download and install the Expression Blend SDK for Silverlight 4 and add a reference to System.Windows.Interactivity.dll.