关于WPF:WPF-PasswordBox数据绑定方法

本文介绍下 PasswordBox 进行数据绑定的办法，本文参考链接。

本文残缺示例程序见 GitHub。

问题形容

PasswordBox 的 Password 属性不是依赖属性，因而无奈进行数据绑定。

解决办法

该问题的解决办法有多种，本文介绍如何通过增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，但因为某种需要附加到该对象上，通过附加属性能够实现将属性与宿主解耦的目标。附加属性实质上就是依赖属性，只是它们在属性包装器和注册时有区别。注册附加属性应用 RegisterAttached 办法，注册依赖属性应用 Register 办法，这两个办法的参数差异并不大。

首先增加一个 PasswordBoxBindingHelper 类，该类蕴含一个附加属性（snippet：propa+ 两次 tab），通过设置该属性的 PropertyChangedCallback 将扭转告诉到 PasswordBox.Password，并通过增加对 PasswordBox.PasswordChanged 事件的响应来响应 PasswordBox.Password 的扭转。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);
}

而后在 View 中应用该附加属性进行数据绑定，本文示例中主窗口蕴含一个 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="查看明码" Command="{Binding ClickedCommand}"/>
        </StackPanel>
    </Grid>
</Window>

//xaml.cs 设置绑定源
public MainWindow()
{InitializeComponent();
    this.DataContext = new MainWindowViewModel();}

最初创立 ViewModel 进行逻辑解决：

// ViewModel
public class MainWindowViewModel : INotifyPropertyChanged
{
    public string Password
    {
        get => _password;
        set
        {
            _password = value;
            OnPropertyChanged();}
    }

    public DelegateCommand ClickedCommand => _clickedCommand ?? (_clickedCommand = new DelegateCommand { ExecuteAction = OnClicked});

    // 应用 CallerMemberName 个性简化代码，并能够防止手动输出谬误
    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;}
}