MVVM WPF 多重绑定不适用于命令参数

Question

我无法使多重绑定适用于两个密码框。我确实在网上阅读了一堆尝试工作示例的文章，但没有一个是我尝试过的相同场景。问题是当我点击登录按钮时，这些密码字段不会传输到命令执行方法。

转换器的 XAML：

<Grid.Resources>
    <converter:PasswordConverter x:Key="passwordConverter"/>
</Grid.Resources>

按钮的 XAML 如下所示：

<Button x:Name="loginButton" 
                Content="Belépés" 
                Margin="494,430,0,0" 
                VerticalAlignment="Top" 
                FontSize="20" 
                RenderTransformOrigin="-2.624,8.99" 
                HorizontalAlignment="Left" 
                Width="172"
                Command="{Binding NavCommand}">
            <Button.CommandParameter>
                <MultiBinding Converter="{StaticResource passwordConverter}" Mode="TwoWay">
                    <Binding Path="Password" ElementName="userIDPasswordBox"/>
                    <Binding Path="Password" ElementName="leaderIDPasswordBox"/>
                </MultiBinding>
            </Button.CommandParameter>
        </Button>

密码转换器代码：

public class PasswordConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        return values.Clone();
    }
    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

中继命令：

public class RelayCommand : ICommand
{
    Action _TargetExecuteMethod;
    Func<bool> _TargetCanExecuteMethod;
    public RelayCommand(Action executeMethod)
    {
        _TargetExecuteMethod = executeMethod;
    }
    public RelayCommand(Action executeMethod, Func<bool> canExecuteMethod)
    {
        _TargetExecuteMethod = executeMethod;
        _TargetCanExecuteMethod = canExecuteMethod;
    }
    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged(this, EventArgs.Empty);
    }
    #region ICommand Members
    bool ICommand.CanExecute(object parameter)
    {
        if (_TargetCanExecuteMethod != null)
        {
            return _TargetCanExecuteMethod();
        }
        if (_TargetExecuteMethod != null)
        {
            return true;
        }
        return false;
    }
    public event EventHandler CanExecuteChanged = delegate { };
    void ICommand.Execute(object parameter)
    {
        if (_TargetExecuteMethod != null)
        {
            _TargetExecuteMethod();
        }
    }
    #endregion
}

视图模型的最后一段代码：

public class LogonViewModel : BaseViewModel
{
private Action _loginActionComplete;
public LogonViewModel(Action loginActionComplete)
{
    _measureTimer = new Timer();
    _measureTimer.Interval = 500D;
    _measureTimer.Elapsed += measureTimer_Elapsed;
    _measureTimer.Start();
    _loginActionComplete = loginActionComplete;
    NavCommand = new RelayCommand(loginActionComplete);
    SerialPort = new SerailCommunicationNameSpace.SerialCommunication("COM3");
}
~LogonViewModel()
{
    SerialPort.Close();
}
public RelayCommand NavCommand { get; private set; }
private double _measuredWeight;
public double MeasuredWeight {
    get
    {
        return _measuredWeight;
    }
    set
    {
        SetProperty(ref _measuredWeight, value);
    }
}
private Timer _measureTimer;
public SerailCommunicationNameSpace.SerialCommunication SerialPort { get; set; }
private void measureTimer_Elapsed(object sender, ElapsedEventArgs e)
{
    var measuredWeight = 0D;
    if (string.IsNullOrWhiteSpace(SerialPort.DataReceived) == false) {
        var dataReceivedStartTrim = SerialPort.DataReceived.TrimStart();
        var dataReceivedNumbersOnly = dataReceivedStartTrim.Substring(0, dataReceivedStartTrim.IndexOf(' '));
        var enUSCultureInfo = new CultureInfo("en-US");
        measuredWeight = double.Parse(dataReceivedNumbersOnly, enUSCultureInfo);
    }
    SetProperty(ref _measuredWeight, measuredWeight);
    OnPropertyChanged("MeasuredWeight");
}
public string LeaderId { get; set; }
public string UserId { get; set; }

}

Answer 1

问题是PasswordBox Password属性既不是依赖属性，也不是实现INotifyPropertyChanged。这意味着，密码的更改不会应用于绑定。
例如，如果将用于PasswordChanged的事件处理程序添加到PasswordBox并将密码设置为 Tag 属性，则可以绑定到Tag，绑定将起作用。

<Button x:Name="loginButton" 
        Content="Belépés" 
        Margin="494,430,0,0" 
        VerticalAlignment="Top" 
        FontSize="20" 
        RenderTransformOrigin="-2.624,8.99" 
        HorizontalAlignment="Left" 
        Width="172"
        Command="{Binding NavCommand}">
    <Button.CommandParameter>
        <MultiBinding Converter="{StaticResource passwordConverter}">
            <Binding Path="Tag" ElementName="userIDPasswordBox"/>
            <Binding Path="Tag" ElementName="leaderIDPasswordBox"/>
        </MultiBinding>
    </Button.CommandParameter>
</Button>
<PasswordBox Name="userIDPasswordBox" PasswordChanged="PasswordBox_PasswordChanged"/>
<PasswordBox Name="leaderIDPasswordBox" PasswordChanged="PasswordBox_PasswordChanged"/>
private void PasswordBox_PasswordChanged(object sender, RoutedEventArgs e)
{
    var pbx = sender as PasswordBox;
    if (pbx!=null)
    {
        pbx.Tag = pbx.Password;
    }
}

当然，为了避免代码隐藏在实现后面，您应该将事件处理程序移动到行为中。