WPF — PasswordBox数据绑定方法

本文介绍下PasswordBox进行数据绑定的方法，本文参考链接。

本文完整示例程序见GitHub。

问题描述

PasswordBox的Password属性不是依赖属性，因此无法进行数据绑定。

解决办法

该问题的解决办法有多种，本文介绍如何通过添加附加属性解决该问题。

附加属性是说一个属性本不属于某个对象，但由于某种需求附加到该对象上，通过附加属性可以实现将属性与宿主解耦的目的。附加属性本质上就是依赖属性，只是它们在属性包装器和注册时有区别。注册附加属性使用RegisterAttached方法，注册依赖属性使用Register方法，这两个方法的参数差别并不大。

首先添加一个PasswordBoxBindingHelper类，该类包含一个附加属性（snippet：propa+两次tab），通过设置该属性的PropertyChangedCallback将改变通知到PasswordBox.Password，并通过添加对PasswordBox.PasswordChanged事件的响应来响应PasswordBox.Password的改变。有了该附加属性，即可进行数据绑定。

public static string GetPasswordContent(DependencyObject obj) => (string)obj.GetValue(PasswordContentProperty);  public static void SetPasswordContent(DependencyObject obj, string value) => obj.SetValue(PasswordContentProperty, value);  public static readonly DependencyProperty PasswordContentProperty =     DependencyProperty.RegisterAttached("PasswordContent", typeof(string), typeof(PasswordBoxBindingHelper),     new PropertyMetadata(string.Empty, OnPasswordContentPropertyChanged));  private static void OnPasswordContentPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {     var box = d as PasswordBox;     box.PasswordChanged -= OnPasswordChanged;     var password = (string)e.NewValue;     if (box != null && box.Password != password)         box.Password = password;     box.PasswordChanged += OnPasswordChanged; }  private static void OnPasswordChanged(object sender, RoutedEventArgs e) {     var box = sender as PasswordBox;     SetPasswordContent(box, box.Password); } 

然后在View中使用该附加属性进行数据绑定，本文示例中主窗口包含一个PasswordBox控件及一个Button按钮：

// xaml 绑定附加属性 <Window ...         xmlns:local="clr-namespace:PasswordBoxBinding"         Title="PasswordBoxBinding" Height="300" Width="450" WindowStartupLocation="CenterScreen">      <Grid>         <StackPanel HorizontalAlignment="Center" Orientation="Horizontal">             <PasswordBox MinWidth="200" Height="30" BorderBrush="LightGray" BorderThickness="2"                          local:PasswordBoxBindingHelper.PasswordContent="{Binding Password,Mode=TwoWay}"/>             <Rectangle Width="20"/>             <Button Width="80" Height="30" Content="查看密码" Command="{Binding ClickedCommand}"/>         </StackPanel>     </Grid> </Window>  //xaml.cs 设置绑定源 public MainWindow() {     InitializeComponent();     this.DataContext = new MainWindowViewModel(); } 

最后创建ViewModel进行逻辑处理：

// ViewModel public class MainWindowViewModel : INotifyPropertyChanged {     public string Password     {         get => _password;         set         {             _password = value;             OnPropertyChanged();         }     }      public DelegateCommand ClickedCommand => _clickedCommand ?? (_clickedCommand = new DelegateCommand { ExecuteAction = OnClicked });      // 使用CallerMemberName特性简化代码，并可以避免手动输入错误     public void OnPropertyChanged([CallerMemberName] string name = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));      private void OnClicked(object o) => MessageBox.Show($"password: {Password}");      public event PropertyChangedEventHandler PropertyChanged;      private DelegateCommand _clickedCommand;     private string _password; }  // 实现ICommand public class DelegateCommand : ICommand {     public bool CanExecute(object parameter) => CanExecuteAction?.Invoke(parameter) ?? true;      public void Execute(object parameter) => ExecuteAction?.Invoke(parameter);      public event EventHandler CanExecuteChanged;      public Action<object> ExecuteAction { get; set; }     public Func<object, bool> CanExecuteAction { get; set; } }