从 XAML 中定义的 ListBoxItems 的 ListBox 中的 PasswordBox 获取密码

Question

我有一个WPFListBox，每个ListBoxItem 有很多UIElements。其中UIElements 之一是PasswordBox。这些UIElements 在Xaml ControlTemplate 中定义。

我需要做的是在后面的代码中从PasswordBox 获取一个Password 字符串。但是我无法绑定PasswordBox 的Password 属性，这不是动态属性，因为Password 不应该长时间存储在内存中。

现在我想到的解决方案是在后面的代码中获取ListBoxItem 中的UIElements，然后从那里获取Password。

但我无法弄清楚如何从 ListBox 获取代码中的 UIElements。

Answer 1

密码框的密码属性不是依赖属性，所以不能绑定该属性。

您可以通过以下任一方式从密码框控件中获取密码。

1. 将密码框控件作为参数传递给项目附加的命令。

   XAML

   <Window x:Class="WpfApplication4.Window1"
       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
       Title="Window1" Height="300" Width="300">
   <StackPanel>
       <PasswordBox Name="txtPassword" VerticalAlignment="Top" Width="120" />
       <Button Content="Ok" Command="{Binding Path=OkCommand}" CommandParameter="{Binding ElementName=txtPassword}"/>
   </StackPanel>
   

背后的代码

public class MyViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        [NotifyPropertyChangedInvocator]
        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
        }

        public ICommand OkCommand { get; private set; }

        public MyViewModel()
        {
            OkCommand = new GeneralCommand<object>(ExecuteOkCommand, param => CanExecuteCommand());
        }

        private void ExecuteOkCommand(object parameter)
        {
            var passwordBox = parameter as PasswordBox;
            var password = passwordBox.Password;
        }

        private bool CanExecuteCommand()
        {
            return true;
        }
    }

这稍微违反了 MVVM 模式，因为现在视图模型知道视图是如何实现的。

1. 使用 attach 属性绑定密码。

XAML

<StackPanel>
    <PasswordBox w:PasswordHelper.Attach="True" 
         w:PasswordHelper.Password="{Binding Text, ElementName=plain, Mode=TwoWay}" 
                 Width="130"/>
    <TextBlock Padding="10,0" x:Name="plain" />
</StackPanel>

代码

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);
    }
}

您可以参考“http://wpftutorial.net/PasswordBox.html”获取详细信息。