我不认为有一个'官方'的方式来做到这一点，我不知道如果你应该。
但您可以在设置值后手动设置光标位置来解决此问题（source）。

private void SetCursor(PasswordBox passwordBox, int index)
{
    passwordBox.GetType().GetMethod("Select", BindingFlags.Instance | BindingFlags.NonPublic).Invoke(passwordBox, new object[] { index, 0 });
}

“hack”绑定：

this.WhenAnyValue(x => x.ViewModel.SecretKey)
    .Where(pw => pw != null)
    .Do(pw =>
    {
        secretKey.Password = pw;
        SetCursor(secretKey, pw.Length);
    })
    .Subscribe()
    .DisposeWith(disposableRegistration);

我最近遇到了类似的问题，下一个解决方案对我来说效果很好。也许能帮到别人。

ViewModel.WhenAnyValue(x => x.Password)
    .Where(password => string.Equals(password, PasswordBox.Password, StringComparison.CurrentCulture) is false)
    .ObserveOn(RxApp.MainThreadScheduler)
    .Subscribe(password => PasswordBox.Password = password)
    .DisposeWith(disposableRegistration);

Observable.FromEventPattern<RoutedEventHandler, RoutedEventArgs>(
        h => PasswordBox.PasswordChanged += h,
        h => PasswordBox.PasswordChanged -= h)
    .Select(_ => PasswordBox.Password)
    .Where(password => string.Equals(password, ViewModel.Password, StringComparison.CurrentCulture) is false)
    .ObserveOn(RxApp.MainThreadScheduler)
    .Subscribe(password => ViewModel.Password = password)
    .DisposeWith(disposableRegistration);

PasswordBox通常由附加属性处理。我做了研究，ReactiveUi绑定不能处理带有附加属性的双向绑定。另一方面，当您使用ReactiveUi时，在XAML中没有绑定的危险信号-不鼓励，但不禁止。考虑到纯ReactiveUi无法实现附加属性，我决定在绑定PasswordBox时例外，我认为这是合理和正确的。
我使用了PasswordHelper，它实现了wpftutorial.net教程中的附加属性

public static class PasswordHelper
{
    public static readonly DependencyProperty PasswordProperty =
        DependencyProperty.RegisterAttached("Password",
        typeof(string), typeof(PasswordHelper),
        new FrameworkPropertyMetadata(string.Empty, OnPasswordPropertyChanged));
 
    public static readonly DependencyProperty AttachProperty =
        DependencyProperty.RegisterAttached("Attach",
        typeof(bool), typeof(PasswordHelper), new PropertyMetadata(false, Attach));
 
    private static readonly DependencyProperty IsUpdatingProperty =
       DependencyProperty.RegisterAttached("IsUpdating", typeof(bool), 
       typeof(PasswordHelper));
 
 
    public static void SetAttach(DependencyObject dp, bool value)
    {
        dp.SetValue(AttachProperty, value);
    }
 
    public static bool GetAttach(DependencyObject dp)
    {
        return (bool)dp.GetValue(AttachProperty);
    }
 
    public static string GetPassword(DependencyObject dp)
    {
        return (string)dp.GetValue(PasswordProperty);
    }
 
    public static void SetPassword(DependencyObject dp, string value)
    {
        dp.SetValue(PasswordProperty, value);
    }
 
    private static bool GetIsUpdating(DependencyObject dp)
    {
        return (bool)dp.GetValue(IsUpdatingProperty);
    }
 
    private static void SetIsUpdating(DependencyObject dp, bool value)
    {
        dp.SetValue(IsUpdatingProperty, value);
    }
 
    private static void OnPasswordPropertyChanged(DependencyObject sender,
        DependencyPropertyChangedEventArgs e)
    {
        PasswordBox passwordBox = sender as PasswordBox;
        passwordBox.PasswordChanged -= PasswordChanged;
 
        if (!(bool)GetIsUpdating(passwordBox))
        {
            passwordBox.Password = (string)e.NewValue;
        }
        passwordBox.PasswordChanged += PasswordChanged;
    }
 
    private static void Attach(DependencyObject sender,
        DependencyPropertyChangedEventArgs e)
    {
        PasswordBox passwordBox = sender as PasswordBox;
 
        if (passwordBox == null)
            return;
 
        if ((bool)e.OldValue)
        {
            passwordBox.PasswordChanged -= PasswordChanged;
        }
 
        if ((bool)e.NewValue)
        {
            passwordBox.PasswordChanged += PasswordChanged;
        }
    }
 
    private static void PasswordChanged(object sender, RoutedEventArgs e)
    {
        PasswordBox passwordBox = sender as PasswordBox;
        SetIsUpdating(passwordBox, true);
        SetPassword(passwordBox, passwordBox.Password);
        SetIsUpdating(passwordBox, false);
    }
}

在XAML中，我对PasswordBox使用标准绑定，并附带属性：

<PasswordBox Name="PasswordBox"
             local:PasswordHelper.Attach="True"
             local:PasswordHelper.Password="{Binding Password, Mode=TwoWay}"/>

在后面的代码中，我将ViewModel绑定到DataContext。

this.WhenActivated(d =>
{
    this.WhenAnyValue(x => x.ViewModel).BindTo(this, x => x.DataContext).DisposeWith(d);
});

您可以在GitHub repository中找到示例应用程序。