WPF MultiBinding

<Window x:Class="WpfDemo.MultiBindingDemo"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MultiBindingDemo" Height="300" Width="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="14*"/>
            <RowDefinition Height="65*"/>
            <RowDefinition Height="190*"/>
        </Grid.RowDefinitions>
        <StackPanel Grid.RowSpan="3">
            <TextBox Height="23" TextWrapping="Wrap" x:Name="txt1" />
            <TextBox Height="23" TextWrapping="Wrap" x:Name="txt2" />
            <TextBox Height="23" TextWrapping="Wrap" x:Name="txt3" />
            <TextBox Height="23" TextWrapping="Wrap" x:Name="txt4" />
            <Button Content="Button" Height="37" x:Name="btn" Click="btn_Click"/>

        </StackPanel>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace WpfDemo
{
    /// <summary>
    /// MultiBindingDemo.xaml 的交互逻辑
    /// </summary>
    public partial class MultiBindingDemo : Window
    {
        public MultiBindingDemo()
        {
            InitializeComponent();
            SetMultiBinding();
        }
        public void SetMultiBinding()
        {
            Binding bind1 = new Binding("Text") { Source = this.txt1 };
            Binding bind2 = new Binding("Text") { Source = this.txt2 };
            Binding bind3 = new Binding("Text") { Source = this.txt3 };
            Binding bind4 = new Binding("Text") { Source = this.txt4 };

            MultiBinding mb = new MultiBinding() { Mode=BindingMode.OneWay };

            mb.Bindings.Add(bind1);
            mb.Bindings.Add(bind2);
            mb.Bindings.Add(bind3);
            mb.Bindings.Add(bind4);

            mb.Converter = new LogonMultiBindingConverter();

            this.btn.SetBinding(Button.IsEnabledProperty, mb);
        }

        private void btn_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("999");
        }
    }

    public class LogonMultiBindingConverter:IMultiValueConverter
    {

        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            //if(values.Any(x=>x==null))
            //{
            //    return false;
            //}

            if(!values.Cast<string>().Any(x=>string.IsNullOrEmpty(x)))
            {
                var array = values.Cast<string>().ToArray();

                if (array[0] == array[1] && array[2] == array[3])
                {
                    return true;
                }
            }
             return false;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}